International Journal of Food Microbiology 61 (2000) 91–125
www.elsevier.nl / locate / ijfoodmicro
Review
Ciguatera: recent advances but the risk remains
a,
b
Leigh Lehane *, Richard J. Lewis
a
National Office of Animal and Plant Health, Agriculture, Fisheries and Forestry — Australia, GPO Box 858, Canberra, ACT 2601,
Australia
b
Queensland Department of Primary Industries, Gehrmann Laboratories, The University of Queensland, Brisbane,
Queensland 4072, Australia
Received 12 April 2000; received in revised form 20 June 2000; accepted 26 June 2000
Abstract
Ciguatera is an important form of human poisoning caused by the consumption of seafood. The disease is characterised by
gastrointestinal, neurological and cardiovascular disturbances. In cases of severe toxicity, paralysis, coma and death may
occur. There is no immunity, and the toxins are cumulative. Symptoms may persist for months or years, or recur
periodically. The epidemiology of ciguatera is complex and of central importance to the management and future use of
marine resources. Ciguatera is an important medical entity in tropical and subtropical Pacific and Indian Ocean regions, and
in the tropical Caribbean. As reef fish are increasingly exported to other areas, it has become a world health problem. The
disease is under-reported and often misdiagnosed. Lipid-soluble, polyether toxins known as ciguatoxins accumulated in the
muscles of certain subtropical and tropical marine finfish cause ciguatera. Ciguatoxins arise from biotransformation in the
fish of less polar ciguatoxins (gambiertoxins) produced by Gambierdiscus toxicus, a marine dinoflagellate that lives on
macroalgae, usually attached to dead coral. The toxins and their metabolites are concentrated in the food chain when
carnivorous fish prey on smaller herbivorous fish. Humans are exposed at the end of the food chain. More than 400 species
of fish can be vectors of ciguatoxins, but generally only a relatively small number of species are regularly incriminated in
ciguatera. Ciguateric fish look, taste and smell normal, and detection of toxins in fish remains a problem. More than 20
precursor gambiertoxins and ciguatoxins have been identified in G. toxicus and in herbivorous and carnivorous fish. The
toxins become more polar as they undergo oxidative metabolism and pass up the food chain. The main Pacific ciguatoxin
(P-CTX-1) causes ciguatera at levels 5 0.1 mg / kg in the flesh of carnivorous fish. The main Caribbean ciguatoxin
(C-CTX-1) is less polar and 10-fold less toxic than P-CTX-1. Ciguatoxins activate sodium ion (Na 1 ) channels, causing cell
membrane excitability and instability. Worldwide coral bleaching is now well documented, and there is a strong association
between global warming and the bleaching and death of coral. This, together with natural environmental factors such as
earthquakes and hurricanes, and man-made factors such as tourism, dock construction, sewage and eutrophication, may
create more favourable environments for G. toxicus. While low levels of G. toxicus are found throughout tropical and
subtropical waters, the presence of bloom numbers is unpredictable and patchy. Only certain genetic strains produce
ciguatoxins, and environmental triggers for increasing toxin production are unknown.  2000 Elsevier Science B.V. All
rights reserved.
Keywords: Ciguatera; Ciguatoxin(s); Gambiertoxins; Fish poisoning; Gambierdiscus toxicus
*Corresponding author. Tel.: 161-2-6272-4697; fax: 161-2-6272-4533.
E-mail address: [email protected] (L. Lehane).
0168-1605 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved.
PII: S0168-1605( 00 )00382-2
92
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
1. Introduction
Ciguatera has been recognised for centuries (Halstead, 1978; Mitchell, 1981; Juranovic and Park,
1991; Lewis and King, 1996). It is perhaps the most
common marine food poisoning known (Hokama,
1993) and the most common foodborne illness
related to finfish consumption (Lange, 1994). It is
most prevalent in tropical and sub-tropical Pacific
and Indian Ocean regions, and in the tropical Carib´ 1997). However, as reef
bean (Bagnis, 1981; Brusle,
fish are increasingly exported to other areas, either
alive, fresh or preserved, ciguatera may occur far
from tropical oceans, and as a result has become a
world health problem.
The epidemiology of the disease is extremely
complex, but remains of central importance to the
future management and use of marine resources.
While ciguatera is probably the most frequently
reported seafood-related illness, considerable underreporting still occurs, which has implications for
both the investigation and control of outbreaks.
The review attempts to address the following key
questions: ‘What causes outbreaks of ciguatera?’,
‘What are the underlying factors contributing to
outbreaks?’ and ‘What are the consequences of
outbreaks?’ While the information is considered
under standard headings used in risk-assessment
(Kindred, 1996; Buchanan, 1998), insufficient numerical data are presently available to allow an
accurate, quantitative characterisation of risk.
2. Hazard identification
Although many uncertainties still exist in relation
to ciguatera, making management and control difficult, there is now little doubt regarding the identification of the hazard that causes the disease. This
progress has been the result of intensive research,
spanning nearly half a century. Major benchmarks in
the history of elucidating the aetiology of ciguatera
were:
• Randall’s hypothesis (Randall, 1958) that the
toxin(s) is introduced into the food chain through
herbivorous fish that feed on toxic microalgae.
• The demonstration by Helfrich and Banner
(1963), who fed ciguateric fish to non-toxic fish,
that the toxin(s) may be passed through the food
chain without apparent harm to the carrier.
• The isolation and naming of ‘ciguatoxin’ (CTX)
from the flesh of the moray eel by Scheuer et al.
(1967).
• The discovery by Yasumoto et al. (1977) of the
dinoflagellate that produces ciguatoxin(s).
• Identification of the structure of the main Pacific
Ocean ciguatoxin and a precursor ciguatoxin in
Gambierdiscus toxicus by Murata et al. (1989).
Subsequently a number of related ciguatoxins, the
causative toxins of ciguatera, have been identified
chemically. Their mechanism of action has been
ascertained and their adverse physiological effects
documented in laboratory animals and humans.
2.1. Ciguateric fish
Ciguatoxins are found most frequently in particular fish species restricted to warmer subtropical
and tropical regions. Among risk species, toxicity of
fish depends largely on the areas where those fish
live and feed. Poisonous fish are generally associated
with coral reefs and are usually bottom dwellers, but
may be pelagic. Toxic reef fish may be found in one
part of a reef and not in another nearby, because reef
fish are generally non-migratory. However, fish are
not simply poisonous or not poisonous. Bagnis
(1986) showed that most of the reef fish in French
Polynesia have low levels of toxin(s), and that this
level can increase rapidly to high-risk concentrations
following a bloom of dinoflagellates.
Halstead (1978) suggested that more than 400
species of fish can be ciguateric, but this figure may
be too high (Juranovic and Park, 1991). Thirty-two
species in 15 families cause ciguatera in Tahiti
(Bagnis, 1969); about 10 species were found toxic in
field studies in the Ryukyus Islands (Hashimoto,
1979); and only 16 species were implicated in 172
cases of ciguatera over a 2-year period in Hawaii
(Kodama and Hokama, 1989).
The moray eel (Lycodontis or Gymnothorax
javanicus) is generally regarded as the most toxic
ciguateric fish, and toxin(s) extracted from it have
been used for research and immunological testing.
Fortunately, the species is not generally eaten (Lewis
and King, 1996), although in some areas of the
Pacific it is a prized species. Serranidae fish, includ-
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
ing species of great commercial value such as coral
trout (Plectropomus spp.), were the most commonly
incriminated in ciguatera, accounting for 50% of
´
outbreaks on Reunion
Island in the south-western
Indian Ocean (Quod and Turquet, 1996). Sours and
Smith (1980), who reported outbreaks in the US
between 1972 and 1978, said that ciguatera was most
often associated with ingestion of grouper (Epinephelus spp.) in Florida and amberjack (Seriola
spp.) in Hawaii. In Miami, Florida, it is illegal to sell
barracuda for human consumption because more than
one-third of them test positive for ciguatoxin (Craig,
1980; De Sylva, 1994).
The main fish species in Australia that have
caused outbreaks of ciguatera are narrow-barred
Spanish mackerel (Scomberomorus commersoni) and
other mackerel species, coral trout (Plectropomus
spp.), flowery cod (Epinephelus fuscoguttatus), barracuda (Sphyraena jello), red emperor (Lutjanus
sebae), queenfish (Scomberoides commersonianus),
grouper (Epinephelus lanciolatus), red bass (Lutjanus
bohar), trevally (Caranx spp.), Maori wrasse
(Chelinus trilobatus), kingfish (Seriola spp.), parrotfish (Scarus spp.), chinaman fish (Symphorus
nematophorus) and paddletail (Lutjanus gibbus)
(Mitchell, 1976; Gillespie et al., 1986; Payne, 1994;
Fenner et al., 1997). In Queensland, there is a ban on
the capture of narrow-barred Spanish mackerel and
barracuda in Platypus Bay, as these fish are frequently toxic.
The ciguatoxins are the major toxins found in
ciguateric fish and are the primary cause of ciguatera. Other toxins and other sources of these toxins
have been suggested as being involved, but their
involvement, if any, remains to be established
(Holmes and Lewis, 1994). P-CTX-1, the principal
ciguatoxin isolated from moray eel viscera, typically
contributes about 90% of total lethality and poses a
health risk at concentrations greater than 0.1 mg / kg
fish (Murata et al., 1990; Lewis, 1994a). Hokama et
al. (1998) suggested 0.08 mg / kg fish as the concentration that causes clinical symptoms in humans
in Hawaii. While viscera such as liver, intestines and
gonads are considerably more toxic than the corresponding muscle (Halstead, 1978; Vernoux et al.,
1985; Schatz, 1989), fish flesh is the most common
cause of ciguatera as it is consumed more often and
in larger quantities than other tissues.
The main ciguatoxins CTX-1, -2 and -3 have
93
different effects in vivo, and are present in fish in
different relative amounts, contributing to the variability of symptoms in human cases of ciguatera
(Lewis et al., 1991; Lewis and Sellin, 1992).
Hokama et al. (1996) suggested that the slight
changes in chemical structure of the ciguatoxins that
occur as they are passed through the food chain
might be the source of some of the observed
diversity in symptoms of ciguatera. The clinical
picture may be further complicated by unrelated
toxins produced by G. toxicus and other dinoflagellates that may accumulate in the food chain of fish,
although any role for such toxins requires substantiation.
It remains to be determined to what extent the
ratio of the different ciguatoxins varies between
ciguateric fish of the same and different species, and
whether the presence of multiple ciguatoxins has
implications for the treatment of ciguatera. Factors
that may contribute to different ratios of the
ciguatoxins in fish include differences in the ratio of
the ciguatoxins and their precursors in the diet of
fish, and differences in the ability of fish to absorb,
metabolise and excrete the toxins (Lewis and Sellin,
1992). Ciguatera may also result from the less-potent
gambiertoxins (ciguatoxin precursors) and less-oxidised ciguatoxins in herbivorous fish (see Lewis and
Holmes, 1993; and Fig. 1).
Factors influencing the concentration of ciguatoxins that accumulate in fish include the rate of dietary
intake, the efficiency of absorption, the degree and
nature of any toxin biotransformation, the rate of
excretion, and the rate of growth of the fish (Lewis
and Holmes, 1993). Toxicity varies from species to
species, from fish to fish, from season to season and
from location to location. Fish in one local area may
have a high level of toxicity, but the same species
nearby may be relatively free of toxin. Safe areas
may suddenly give rise to toxic fish, and then
eventually return to being safe.
Excretion of ciguatoxins from fish is slow. An
estimation of excretion, including biotransformation
to less potent forms, from a family of moray eels in
the central Pacific indicated a half-life of 264 days.
Rapid declines in the incidence of ciguatera (90–300
days for a 50% decline) seen at some other locations
in the Pacific may be the result of a similar half-life
for the decline of ciguatoxin levels in fish (Lewis et
al., 1992; Lewis and Holmes, 1993). Such excretion
94
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
Fig. 1. Structure of Pacific and Caribbean ciguatoxins. Shown are P-CTX-1 (Murata et al., 1990), P-CTX-3 (Lewis et al., 1991, 1993a),
P-CTX-4B (Murata et al., 1990), P-CTX-3C (Satake et al., 1993), and C-CTX-1 (Lewis et al., 1998). The energetically less favoured
epimers, P-CTX-2 (52-epi P-CTX-3; Lewis et al., 1993a), P-CTX-4A (52-epi P-CTX-4B; Satake et al., 1998), and C-CTX-2 (56-epi
C-CTX-1; Lewis et al., 1998) are indicated in parenthesis. 2,3-DihydroxyP-CTX-3C and 51-hydroxyP-CTX-3C have also been isolated from
Pacific fish (Satake et al., 1998).
may mean that toxicity does not necessarily increase
with increasing size in all carnivorous fish (Lewis
and Holmes, 1993).
While toxic fish have normal appearance, taste and
smell, higher levels of ciguatoxins may cause behavioural and morphological changes in the fish, and
even death (Halstead, 1978; Davin et al., 1986;
´ 1997).
Capra et al., 1988; Lewis, 1992a; Brusle,
Lewis (1992a) and Lewis and Holmes (1993) suggested that the lethal effects of ciguatoxins in fish
might impose an upper limit on the levels they can
carry, which could limit the incidence of human
deaths associated with ciguatera. Fish in the wild
may succumb to ciguatoxins and / or maitotoxins and
be preferentially preyed upon (Lewis and Holmes,
1993).
In the herbivorous surgeonfish (Ctenochaetus
striatus, or maito), water-soluble maitotoxin is the
predominant toxin in the alimentary tract, both
maitotoxin and ciguatoxin are present in the liver,
and only ciguatoxin is present in the flesh (Yasumoto
et al., 1971). There is little evidence that maitotoxin
accumulates in the flesh of surgeonfish, or other fish
(Holmes and Lewis, 1994). Despite the widespread
occurrence of maitotoxins in the benthos (at the
bottom of the sea), maitotoxins are unlikely to cause
human poisoning because of their poor accumulation
in fish flesh and their relatively low oral potency (see
Lewis and Holmes, 1993). Endean et al. (1993a,b)
found unidentified water-soluble substances in the
flesh of narrow-barred Spanish mackerel, one of
which tested positively for alkaloids, but these
substances also have no clear role in ciguatera
(Holmes and Lewis, 1994).
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
2.2. Source of ciguatoxins: the dinoflagellate,
Gambierdiscus toxicus
The idea that a marine alga was the cause of
ciguatera was advanced by Randall (1958). In reviewing ciguatera with particular reference to the
source of the poison, Randall (1958) presented what
he termed a ‘new hypothesis’ on the origin of the
disease. Although the claim that the hypothesis was
new was contested by Halstead (1978), Randall’s
(1958) review of the algal-food chain theory was
valuable and timely. In summary, it proposed that:
• fish become poisonous because of some factor in
their environment;
• the toxicity is associated with food supply;
• the basic poisonous organism is benthic, and
possibly an alga;
• the organism producing ciguatoxin may be one of
the first growing on new or denuded surfaces in
tropical seas in normal ecological succession; and
• the toxin is passed in the food chain to large
predacious fish, which are the most poisonous.
In 1977, Yasumoto et al. reported experiments to
determine whether a benthic dinoflagellate, tentatively identified as Diplopsalis sp., was the cause of
ciguatera. Diplopsalis sp. was first found in a toxic
sample of detritus collected from the surface of dead
coral from the Gambier Islands, French Polynesia.
Extraction of this material and fractionation of the
extracts with solvents yielded two major toxic fractions containing at least one diethyl ether-soluble
toxin and one acetone-precipitable toxin. These were
compared with reference ciguatoxin from the liver of
moray eel (P-CTX-1). The ether-soluble toxin from
the dinoflagellate was judged to resemble reference
ciguatoxin on the basis of various column and thinlayer chromatographic properties, and was indistinguishable from ciguatoxin in a specific pharmacological test. The acetone-precipitable toxin resembled
maitotoxin, which had been isolated from ciguateric
surgeonfish. The amounts of toxins found in the
samples of detritus were proportionally related to the
number of Diplopsalis cells in the detritus.
Diplopsalis was subsequently renamed Gambierdiscus toxicus by Adachi and Fukuyo (1979). G.
toxicus (diameter about 80 mm) is a photosynthetic
species that normally grows as an epiphyte and has a
95
relatively slow growth rate of approximately one
division every 3 days. In its coral reef habitat, G.
toxicus may swim if disturbed, but is usually found
attached to certain macroalgae of coral reefs (see
Withers, 1982). The dinoflagellate may also be found
associated with macroalgae on sand (Holmes et al.,
1994).
It is now known that at least 30 species of
dinoflagellates produce bioactive compounds, including some toxins that are among the most potent
non-proteinaceous poisons known (Yasumoto and
´ 1997). Some scientists believe
Murata, 1993; Brusle,
that the diverse symptoms of ciguatera are a result of
a combination of several toxins and / or their metabolites, produced by one or more dinoflagellates (Tindall et al., 1984; Juranovic and Park, 1991). However, G. toxicus, which is found on a variety of
macroalgae eaten by herbivorous fish, is now widely
considered the principal cause (Bagnis et al., 1980;
Lewis and Holmes, 1993).
Gillespie et al. (1985) found that population
densities of G. toxicus varied considerably between
locations on the coast of Queensland, and there was
considerable variation in toxin production between
populations. It was later found that only certain
genetic strains of G. toxicus produce gambiertoxins
(Holmes et al., 1991; Satake et al., 1993, 1996).
Holmes et al. (1991) found that gambiertoxins from
cultured G. toxicus competitively inhibited the binding of [ 3 H]brevetoxin-3 to rat brain membranes in a
dose-dependent manner and were more potent than
ciguatoxin (on a per mouse unit basis) at stimulating
neural elements of guinea pig atria.
2.3. Structure and chemistry of ciguatoxins
The neurotoxin primarily responsible for the
symptoms of ciguatera was isolated in a partially
pure form from the flesh of the moray eel and named
ciguatoxin (CTX) by Scheuer et al. (1967). (The
fraction almost certainly contained the major Pacific
ciguatoxin P-CTX-1.) However, variable clinical
signs and symptoms of ciguatera (Bagnis et al.,
1974; Lewis et al., 1988; Kodama and Hokama,
1989) suggested the involvement of several toxins.
Subsequently, chromatographic studies on the lipidsoluble toxic component of ciguateric fish revealed
the presence of several less-polar toxins of ciguatoxin (Chungue et al., 1977; Lewis and Endean, 1984;
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
96
Vernoux and Abbad El Andaloussi, 1986; Legrand et
al., 1990, 1992).
The isolation, purification and characterisation of
ciguatoxins have been hampered by limited availability of authentic ciguateric fish, lack of a specific
sensitive assay, and the low concentration and heterogeneity of toxins present in specimens. However,
it has now been established that the ciguatoxins are
lipid-soluble polyether compounds consisting of 13–
14 rings fused by ether linkages into a mostly rigid,
ladder-like structure (Murata et al., 1990, 1992;
Lewis et al., 1991, 1993a; Satake et al., 1993, 1996;
Lewis et al., 1998). They are relatively stable
molecules that remain toxic after cooking and exposure to mild acidic and basic conditions.
Murata et al. (1989, 1990) determined the structure of ciguatoxin from moray eel and its likely
precursor from G. toxicus (gambiertoxin-4B, or
GTX-4B) on the basis of nuclear magnetic resonance
and mass spectral measurements. Both toxins are
cyclic polyethers resembling the brevetoxin class of
toxins. P-CTX-1 has a molecular weight of 1111.6
and a molecular formula of C 60 H 86 NO 19 (Yasumoto
and Murata, 1990). In its purest chemical state,
CTX-1 is a white powder. It is one of the most
potent mammalian toxins known, lethal in minute
doses (Table 1). CTX-1 is the major toxin present in
ciguateric carnivorous fish on the basis of both
quantity and total toxicity. Herbivorous species often
accumulate gambiertoxins and less-polar ciguatoxins.
Lewis et al. (1991) isolated and characterised
three major ciguatoxins from moray eel viscera by
high-performance liquid chromatography (HPLC)
and proposed the names P-CTX-1, -2 and -3. On the
basis of comparison with the published structure for
(Pacific) ciguatoxin (P-CTX-1) and its congener
GTX-4B (Murata et al., 1990), Lewis et al. (1991,
1993a) proposed structures for CTX-2 and CTX-3
(Fig. 1). Several minor toxins were also detected.
They suggested that gambiertoxins are precursors of
ciguatoxins that are oxidised to ciguatoxins, possibly
through cytochrome enzymes in the livers of fish.
CTX-3 is apparently an intermediate in the metabolism of GTX-4B to CTX-1. On the basis of nuclear
magnetic resonance and HPLC, CTX-2 appears to
originate from a precursor different from GTX-4B.
Lewis and Holmes (1993) called this precursor
GTX-4A, and presented a model showing that GTX4A could give rise to both GTX-4B and CTX-2. In
the biotransformation of GTX-4B to CTX-1 there is
a 10-fold increase in potency (Murata et al., 1990).
Lewis and Sellin (1992) utilised HPLC, mass
spectrometry (MS) and mouse bioassay signs to
confirm that CTX-1, -2 and -3 are the major
ciguatoxins in the flesh of ciguateric fish in the
western Pacific Ocean. The three toxins, respectively, were present at levels of 0.19, 0.09 and 0.02
mg / kg in pooled samples of muscle from 13 narrowbarred Spanish mackerel, each implicated in a ciguatera incident, collected over a 4-year period. They
also identified two minor toxins, thought to be
oxidised analogues. Levels of these toxins in coral
Table 1
Origin and toxicity of chemically defined ciguatoxins
Ciguatoxin
Origin
[M1H] 1 a
Potency
(mg / kg)b
P-CTX-4A
G. toxicus
Herbivorous fish
G. toxicus?
Herbivorous fish
Carnivorous fish
Carnivorous fish
Carnivorous fish
G. toxicus
Carnivorous fish
Carnivorous fish
Carnivorous fish
Carnivorous fish
1061
2
1061
4
1095
1095
1111
1045
1057
1039
1141
1141
2.3
0.9
0.25
2
1.8
0.27
3.6
1
P-CTX-4B
P-CTX-2
P-CTX-3
P-CTX-1
P-CTX-3C
2,3-DihydroxyP-CTX-3C
51-HydroxyP-CTX-3C
C-CTX-1
C-CTX-2
a
b
Protonated molecular mass ([M1H] 1 ).
Intraperitoneal LD 50 dose in mice.
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
trout and blotched javelin were also determined. The
levels of the main three toxins in all three fish tested
were considerably less than those found in the
viscera of moray eel, which were 10.1, 5.8 and 2.1
mg / kg for CTX-1, -2 and -3, respectively (Lewis et
al., 1991).
Legrand et al. (1992) identified nine gambier /
ciguatoxins in G. toxicus, five in the herbivorous
parrotfish and nine in the moray eel, and characterised them into four groups by HPLC and mass
spectra. The increasing polarity of the toxins suggested that they undergo oxidative metabolism during the course of the food chain, becoming more
polar.
The structures of a number of ciguatoxins isolated
from cultured G. toxicus have now been determined.
CTX-3C closely resembles precursor GTX-4B
(Satake et al., 1993), and chromatographic and
spectral comparisons of CTX-4A from cultures of G.
toxicus showed that it was identical with scaritoxin
(Satake et al., 1996), earlier identified in the flesh of
the parrotfish (Scarus gibbus) (Bagnis et al., 1974;
Chungue et al., 1977).
Epidemiological studies suggest that Caribbean
and Indian Ocean ciguatoxins may be different from
Pacific ciguatoxins: gastrointestinal signs are more
prominent and neurological symptoms less prominent in the Caribbean, and fatalities more common in
the Indian Ocean, than the incidence generally
reported in the Pacific (Lewis et al., 1988).
Vernoux and Lewis (1997) isolated and characterised the ciguatoxins from the horse-eye jack (Caranx
latus), a pelagic fish commonly implicated in ciguatera in the Caribbean, and confirmed that Caribbean
ciguatoxins do indeed differ from Pacific ciguatoxins. Caribbean CTX-1 (C-CTX-1) is less polar than
P-CTX-1, and using mouse potency as a guide to
human poisoning potential (based on a mouse intraperitoneal LD 50 value of 3.6 mg / kg bodyweight for
C-CTX-1), > 1.0 mg / kg C-CTX-1 would need to
accumulate in fish, compared with > 0.1 mg / kg
P-CTX-1. The mouse intraperitoneal LD 50 toxicity
of P-CTX-1 has been determined at 0.45 mg / kg
(Tachibana, 1980) and 0.25 mg / kg (Lewis et al.,
1991), the difference probably being accounted for
by different strains of mice. The structures of two
major Caribbean ciguatoxins C-CTX-1 and C-CTX-2
were recently determined (Lewis et al., 1998) and
are compared with the structures of the Pacific
97
ciguatoxins in Fig. 1. The specific origin and potency
of these ciguatoxins are compared in Table 1.
Maitotoxins are generally referred to as water
soluble, although they are soluble in a range of
organic solvents. They have a cyclic polyether
structure (Murata et al., 1993), as do the gambiertoxins and ciguatoxins. The type of maitotoxin produced
by G. toxicus depends on the strain being cultured,
with each strain apparently producing only one type
of maitotoxin (Holmes and Lewis, 1994). Maitotoxins have up to 32 ether rings and, while they are
analogous in structure to ciguatoxin, they have no
partial structure corresponding to ciguatoxin.
Maitotoxins are more lethal than ciguatoxin by the
intraperitoneal route in mice (LD 50 value of 0.13
versus 0.25 mg / kg), but are about 100-fold less toxic
by the oral route of administration.
2.4. Mechanism of toxicity
2.4.1. Mammals
Early studies by Li (1965) concluded mistakenly
that ciguatoxin possessed anticholinesterase activity.
Rayner (1972) first showed that the mechanism of
action of ciguatoxin is related to its direct effect on
voltage-sensitive sodium ion (Na 1 ) channels in
excitable membranes. Na 1 channels are critical to
the function of nerve and muscle, mainly in their
ability to generate and propagate action potentials.
They form pores in the plasma membrane, allowing
passive but selective movements of Na 1 ions down
the electrochemical gradient. Gating systems, which
depend on both membrane potential and time, control the opening and closing of pores (Benoit, 1998).
When Na 1 permeability is increased, the plasma
membrane is unable to maintain the internal environment of cells and volume control. The end result is
an alteration of the electrical properties of the cell,
cell and mitochondrial swelling, and bleb formation
on cell surfaces (Ballantyne et al., 1995; Lewis et al.,
2000).
Bidard et al. (1984) showed that ciguatoxin stimulates excessive Na 1 entry through quasi-irreversible
binding to the Na 1 channel. Later, Lombet et al.
(1987) showed that ciguatoxin acted at the same site
as brevetoxin (site 5) on the Na 1 channel. The
physiological consequence of the binding of
ciguatoxins to channel site 5 is an initial increase in
cellular excitability, which results in spontaneous
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L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
and repetitive firing of action potentials, followed by
a decrease in excitability as the membrane further
depolarises (Lewis et al., 2000).
CTX-1, -2 and -3 have an affinity for voltagedependent Na 1 channels (ED 50 5 0.2–0.9 nM) that
is proportional to their intraperitoneal LD 50 values in
mice (Lewis, 1994a) and each competitively inhibit
the binding of [ 3 H]brevetoxin to Na 1 channels
(Lewis et al., 1991). Legrand and Lotte (1994)
demonstrated that CTX-1 and CTX-4B also competitively inhibit binding of brevetoxin. The affinity of
CTX-1 was about 30 times higher than that of
brevetoxin, while CTX-4B had about the same
affinity as brevetoxin. The inherent sensitivity of the
binding assay suggests that it could be used to
evaluate the toxicity of ciguateric fish.
Capra and Cameron (1988) found that ciguatoxin
significantly reduced amplitude and conduction velocity in rat tail nerves, while increasing latency.
Lignocaine reversed the effects of ciguatoxin towards control values, while ethanol and verapamil
exacerbated the effects of ciguatoxin. Both lignocaine and verapamil significantly reduced the
increased magnitude and duration of the supernormal
period induced by ciguatoxin in rats, consistent with
the enhancement of Na 1 channel conductance.
(Supernormality is a period of increased sensitivity
that occurs in normal nerves for a 6–10-ms period
after an impulse is conducted.)
Cameron et al. (1991a,b) later demonstrated that
ciguatoxin exerts a significant slowing of nerve
conduction velocity and prolongation of the absolute
refractory and supernormal periods of human nerves.
According to Cameron and Capra (1993), sensory
discomfort, particularly in relation to cold, is most
likely a result of exaggerated and intense nerve
depolarisations in small A-d myelinated and C-polymodal nociceptor fibres. Gybels et al. (1979) had
demonstrated previously that trains of stimuli in
C-polymodal nociceptor fibres produce a subjective
feeling of prickling pain at lower frequencies, and a
prolonged stinging, burning or dull pain at higher
frequencies, of discharge. The sensation of itch is
experienced during activation of specific C fibres
(Schmelz et al., 1997) also experienced during lower
frequency discharges in C-polymodal nociceptive
fibres. Nakano (1983) described diffuse slowing of
brain electrical activity, elevated cerebrospinal fluid
pressures and abnormal brainstem auditory-evoked
responses in some patients. The above findings are
consistent with the conclusion that ciguatoxin causes
an abnormal prolongation of Na 1 channel opening in
nerve membranes in vivo.
Ciguatoxins cause a rapid decrease in body temperature (Lewis et al., 1993b; Peng et al., 1995). The
latter authors found, by immunostaining a biomarker
for neuroexcitability, that this was the result of
neuroexcitatory actions of ciguatoxin on brain-stem
regions receiving vagal afferents and ascending
pathways associated with visceral and thermoregulatory responses. Cardiovascular effects are thought to
result from a positive inotropic effect of the toxin on
the myocardium (Lewis and Endean, 1986; Lewis,
1988). When ciguatoxin affects voltage-dependent
Na 1 channels causing Na 1 to move intracellularly,
normal cellular mechanisms are less efficient at
extruding calcium (Lewis and Endean, 1986; Swift
and Swift, 1993). Much of the increased calcium is
buffered by the sarcoplasmic reticulum, making it
available for calcium-induced calcium release, which
results in an increase in the force of cardiac muscle
contraction (Lewis and Endean, 1986).
Ciguatera causes profuse diarrhoea in humans and
mice. Diarrhoea is prevented in mice pretreated with
atropine, suggesting a direct action of the toxin on
cholinergic autonomic nerves (Terao et al., 1991), as
observed in in vitro studies (Lewis and Endean,
1984).
Nakano (1983) reported elevated levels of creatine
phosphokinase (CPK, a muscle enzyme) in the blood
from seven men affected with ciguatera on Midway
Island, Central Pacific. In all the men, the CPK level
rose to . 1000 IU / l (the normal value is , 200
IU / l), but returned to normal in 10 days.
In contrast to the effects of ciguatoxins on Na 1
channels in nerves and muscles, maitotoxin directly
stimulates the movement of calcium ions (Ca 21 )
across biomembranes into cells (Takahashi et al.,
1982; Lewis et al., 2000).
2.4.2. Fish
Individual tropical fish can carry sufficient
ciguatoxin in their tissues to poison several humans,
without showing obvious pathology. However,
ciguatoxin has been shown to be lethal to freshwater
fish (Lewis, 1992a) and marine fish (Capra et al.,
1988). Fish embryos are also susceptible to ciguatoxin, which may represent an unrecognised threat to
the reproductive success of reef fish (Edmunds et al.,
1999).
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
Neurophysiological studies (Flowers et al., 1987)
and 22 Na 1 efflux studies (Capra et al., 1987) indicate
that the Na 1 channels of marine fish are susceptible
to ciguatoxin, and that ciguatoxin exerts similar
effects on fish and mammalian Na 1 channels. Hahn
et al. (1992) demonstrated, for narrow-barred Spanish mackerel, that ciguatoxin associates with at least
one monomeric soluble protein of molecular weight
37 000–40 600 from toxic fish muscle. Capra (1997)
suggested that this may be the basis of a sequestration mechanism that diminishes the binding of
ciguatoxin to the target sites of the Na 1 channels of
excitable membranes in fish.
2.5. Pathology
Allsop et al. (1986) found oedema in Schwann
cell cytoplasm immediately abutting axons, with
axonal compression and vesicular degeneration of
myelin, in human nerve biopsies from people suffering from ciguatera. Using electron microscopy,
Capra and Cameron (1988) found that fluid accumulated in the periaxonal space and displaced and
indented the axon in nerves of rats exposed to
ciguatoxin. Recent work has confirmed that
ciguatoxin causes axonal and Schwann cell swelling
(see Lewis et al., 2000).
In a histological study, Coombe et al. (1987)
found damage to the small intestine of mice that was
inversely related to death time. There was characteristic expansion and rupture of the lamina propria
within the tips of the villi, associated with vascular
and lymphatic disruption. The results suggested that
the pathological changes in the small and large
intestines might be a direct effect of ciguatoxin.
Animals exposed to higher doses of ciguatoxin
succumbed to the neurotoxic effects of the toxin
before major structural changes were manifest. In a
separate study of the diarrhetic effects of ciguatoxin
in mice, Ito et al. (1996) found that a large quantity
of mucus was secreted from even immature goblet
cells lining the colon, and epithelial cell damage
occurred in the upper, but not lower, portion of the
large intestine.
2.6. Clinical characteristics and treatment
2.6.1. Pharmacokinetics
There is little information on the pharmacokinetics
(absorption and plasma kinetics, distribution, metab-
99
olism and excretion) of ciguatoxins in humans or
other mammals. Since ciguatoxins are fat soluble,
absorption from the gut is rapid and substantial,
although an early onset of vomiting and diarrhoea
may assist in expelling some of the toxins before
they are absorbed. When ciguatoxin is administered
to mice by the oral or the intraperitoneal route, there
is little difference in toxicity, which suggests that
oral absorption may be complete or near complete in
this species. As cleaning ciguateric fish can cause
tingling of the hands and eating them can cause
altered sensation in the oral cavity and dysphagia
(Sutherland, 1983; Tonge et al., 1967; Morris et al.,
1982; Ruff and Lewis, 1994), it would appear that
ciguatoxins can penetrate the skin and mucous
membranes. The related brevetoxins also have this
property (Mehta et al., 1991).
Ciguatoxins are likely to be carried in the blood
bound to proteins such as human serum albumin.
Ciguatoxins are present in breast milk (Bagnis and
Legrand, 1987) and are able to cross the placenta and
affect the fetus (Pearn et al., 1982). It seems that the
toxins may be excreted in other body fluids, as there
is apparent sexual transmission, as evidenced by
localised pain after intercourse in partners of affected
people (see Ruff and Lewis, 1994).
Dysuria, or painful urination, has been reported as
a clinical feature of ciguatera (Mitchell, 1981), and
22% of patients in Queensland reported by Gillespie
et al. (1986) had dysuria. This would suggest that
ciguatoxins are either excreted in the urine, or that
nerves lining the urinary tract are sensitised by
ciguatoxin.
There is clinical evidence to suggest that ciguatoxins accumulate in the human body and may be
reactivated from time to time to cause further clinical
symptoms. They could be bound to Na 1 channels or
stored in fat tissue. They may also attach to proteins,
as demonstrated for fish muscle by Hahn et al.
(1992). If stored in adipose tissue, ciguatoxins are
probably not a problem unless the tissue is broken
down rapidly, for example under conditions of
sudden weight loss.
Poli et al. (1990) studied the distribution and
elimination of the related polyether brevetoxin
(PbTx-3) in rats. After intravenous administration,
[ 3 H]PbTx-3 was cleared from the blood rapidly. Less
than 10% remained after 1 min. Within 30 min,
radiolabel distributed to skeletal muscle (69.5%),
liver (18%) and intestinal tract (8%). Over 24 h, it
100
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
decreased in muscle, remained constant in liver, and
increased in the intestinal tract and faeces. The
radioactivity remaining in the carcass after 24 h
(11.7%) was not significantly different from that
after 6 days (9%). This included label in body fat
and all other tissues. As body fat is poorly vascularised, and brevetoxin is highly lipophilic, radiolabel
would be expected to stay in fat for some weeks. The
distribution and elimination profile suggested that the
liver was the major organ of metabolism and that
biliary excretion was an important route of elimination. Thin-layer chromatography confirmed the presence of brevetoxin metabolites in faecal extracts.
Skeletal muscle did not appear to be a site of
metabolism, but rather a storage compartment, from
which toxin was slowly released prior to clearance
by the liver. Given the similar structure of ciguatoxin
and brevetoxin, it is likely that their pharmacokinetics are also similar, and that the biliary /
faecal route is the major route of elimination for both
groups of toxins.
2.6.2. Clinical signs and symptoms and diagnosis
The clinical syndrome of ciguatera is variable,
depending on the type and amount of toxin present,
and on the individual’s susceptibility. Time to onset
of symptoms is also variable and on average appears
inversely related to dose. Gillespie et al. (1986) gave
the usual time of onset of symptoms as 1–6 h, with
onset in 90% of cases being within 12 h; and Lewis
et al. (1988) reported 1–70 h, with a mean of 6.4 h.
Glaziou and Legrand (1994) reported that symptoms
appear 2–30 h after ingestion of toxic fish.
In its typical form, ciguatera is characterised
initially by the onset of intense vomiting, diarrhoea
and abdominal pain within hours of ingestion of
toxic fish. In cases where gastrointestinal symptoms
are absent, paraesthesias (tingling, crawling or burning sensation of the skin) are often the first symptoms. An unusual and perhaps pathognomonic sensory discomfort triggered by cold stimuli is also
frequently reported. This has been described as
‘paradoxical’ sensory disturbance, or ‘reversal’ of
temperature perception to a cold stimulus (Halstead,
1978; Bagnis et al., 1979; Lawrence et al., 1980).
However, Cameron and Capra (1993) consider the
symptoms are more specifically intense and painful
tingling, burning or hot, dry-ice or electric-shock
sensations, rather than a simple perception of cold
feeling hot. Bagnis et al. (1979) reported this disturbance in 87.6% of 3009 cases studied in the South
Pacific region. Other symptoms, including dysaesthesia (painful sensation) in the arms, legs and perioral region, myalgia, aching joints, muscle cramping,
weakness, pruritus and sweating, have a slower onset
(Tonge et al., 1967; Halstead, 1978; Bagnis et al.,
1979; Lawrence et al., 1980). Perceptions of loose
teeth are also common (Caplan, 1998). Hallucinations occur in , 5% of cases in the Pacific (Bagnis
et al., 1979), but in about 16% of cases in the Indian
Ocean (Quod and Turquet, 1996).
Gastrointestinal effects usually consist of an acute,
self-limiting syndrome akin to gastroenteritis, which
may be severe but generally lasts less than 24–36 h.
Resulting dehydration and electrolyte disturbances
may be severe, particularly in young children (Ruff
and Lewis, 1994).
Disturbed vasomotor regulation, including poor
blood pressure control, occurs in about 15% of
ciguatera patients. Systolic blood pressure may typically be reduced to 60–70 mmHg and be followed
by irregular attacks of hypertension. Patients may
exhibit bradycardia (pulse rate slowing to 40–50
beats / min) or tachycardia (irregular, accelerated
pulse rate, often reaching 100–120 beats / min) (Bagnis et al., 1979). Geller and Benowitz (1992) investigated the pathophysiology of orthostatic hypotension
lasting 4 weeks in a 53-year-old female patient with
ciguatera. They excluded blood volume depletion as
a cause, and concluded that the hypotension was the
result of both parasympathetic excess and sympathetic failure.
The neurological disturbance usually resolves
within weeks of onset, although some nervous
symptoms may persist for months or years. Symptoms such as pruritus, arthralgia and fatigue can also
persist for months or years (Gillespie et al., 1986).
According to Bagnis (1993), some individuals intoxicated 25 years previously experience a recurrence of
the main neurological disturbances during periods of
overwork, fatigue or stress. Analysis of ciguatoxins
in blood samples suggests that they can be stored in
the body for several years and cause recurring
symptoms during periods of stress, such as exercise,
weight loss, or excessive alcohol consumption (Barton et al., 1995).
Not only does immunity not follow an attack of
ciguatera, but also there is evidence from a variety of
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
locations that second and subsequent attacks tend to
be more severe than first attacks (Bagnis et al.,
1979). In addition, the frequency of first poisoning is
higher in older individuals, as is the severity of acute
symptoms and the duration of symptoms, suggesting
´ 1997).
prior subclinical toxin exposure (Brusle,
A small number of sufferers complain of an
allergy-like syndrome that can last several years. In
these cases, symptoms typical of ciguatera can be
brought on by the consumption of non-toxic fish,
such as cold-water species. Non-fish products such
as chicken, pork, canned beef, eggs and nuts may
occasionally cause similar problems (Gillespie et al.,
1986; Bagnis, 1993). It has been claimed that eating
the meat of pigs and poultry that have been fed on
fishmeal can exacerbate symptoms, but this has not
been proved (Mitchell, 1981). To avoid possible
relapse, it is recommended that people refrain from
eating fish, including shellfish, for 3–6 months after
confirmed ciguatera (Bourdy et al., 1992; Lewis and
King, 1996).
Gillespie et al. (1986) found that sensitivity to
alcohol may persist for years after the first attack,
and consumption of alcohol caused a recurrence of
symptoms in 28% of Queensland victims studied.
Alcohol consumption may also increase the severity
of the initial illness. While the reason for this is not
known, Cameron and Capra (1991) confirmed the
association in an experimental model. They found
that a blood alcohol content of 0.05% significantly
increased the magnitude and duration of the supernormal response in the tail nerves of ciguatoxintreated rats in vivo.
Ciguatoxin has been associated with a number of
other disorders. Stommel et al. (1991) reported the
development of polymyositis in two people several
years after they suffered severe ciguatera fish toxicity; and ciguatoxin has been detected in blood
samples from some people diagnosed with chronic
fatigue syndrome (see Barton et al., 1995).
Severe cases of ciguatera represent , 10% of total
cases, and on a worldwide scale the number of
hospitalised people is , 5%. Complete recovery
typically takes from a few days to 1 week in mild
intoxications, and from several weeks to months or
even years in severe attacks (Bagnis, 1993). Death,
which results from either respiratory failure or shock,
occurs most often when the most toxic parts of fish
(liver, roe) are consumed, and the case mortality rate
101
is , 0.5% (Hokama and Miyahara, 1986; Lange,
1987, Bagnis, 1993) (and see Section 3.5).
Since there is no reliable diagnostic test for
ciguatera in humans, the diagnosis depends on
clinical criteria, but no standard case definition is
available (Glaziou and Legrand, 1994). Diagnosis
may be complicated by the presence of other types of
toxin, such as maitotoxin or saxitoxin, as well as
ciguatoxins (Schatz, 1989; Whittle and Gallacher,
2000).
2.6.3. Effect on the embryo /fetus and breast-fed
infant
Although the vast majority of ciguatera cases are
caused by ingestion of toxic fish, various forms of
person-to-person transmission have been described,
and are indicative of the potent, lipid-soluble nature
of the ciguatoxins (Ruff and Lewis, 1994). These
include transmission via milk to breast-fed infants
(Bagnis and Legrand, 1987; Blythe and De Sylva,
1990; Karalis et al., 2000), although hyperaesthesia
of the nipples of a lactating mother may interfere
with breast feeding (Pearn et al., 1982). A number of
case reports have demonstrated that ciguatoxins cross
the placenta and may affect the embryo / fetus in a
reversible way.
Fenner et al. (1997) reported severe gastrointestinal and neurological symptoms in a woman in the
first trimester of pregnancy. She was treated with
mannitol, which was quickly effective. Twenty-eight
weeks later, she gave birth to a baby who suffered
mild respiratory distress and was very irritable soon
after birth. He was successfully treated for persistent
pulmonary hypertension of the newborn, which was
not attributed to ciguatoxins.
Senecal and Osterloh (1991) described a severe
episode in a woman during the second trimester. She
felt increased fetal movements 1 h after the poisonous meal and experienced multisystemic symptoms
typical of ciguatera for 8 weeks. Immunoassay and
two bioassays confirmed the presence of ciguatoxin
in the fish. The newborn infant was normal.
Pearn et al. (1982) reported the case of a woman
who had eaten ciguateric coral trout 2 days before
the expected birth of a child. Within 4 h of ingesting
the fish, she experienced characteristic gastrointestinal and neurological symptoms and felt alarming
fetal movements, which continued strongly for 18 h,
then gradually decreased over the next 24 h. A baby
102
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
delivered by Caesarean section 2 days later exhibited
left-sided facial palsy, possible myotonia of the small
muscles of the hands, and respiratory distress
syndrome, but was normal by 6 weeks.
2.6.4. Treatment
Bourdy et al. (1992) documented many traditional
remedies used in the Western Pacific for the treatment of ciguatera. Plants of 64 species are reputed to
be effective, in either a preventive or curative way.
The authors questioned the ‘preventive’ remedies,
because of the heat-resistant and water-soluble properties of ciguatoxin. However, they believed that
some plant species having antidiarrhoeal, antispasmodic, antipruritic or cardiac-tonic effects might
relieve symptoms.
Modern therapy remains primarily symptomatic
and supportive, and is discussed in detail by Ruff
and Lewis (1994). The most favoured treatment at
present is intravenous mannitol (Palafox et al., 1988;
Pearn et al., 1989; Fenner et al., 1997). Mannitol
(1.0 g / kg bodyweight in a 20% solution) is infused
intravenously over about 30 min (Ruff and Lewis,
1994). Mannitol is an obligatory osmotic diuretic. It
is confined to the extra-cellular space and readily
crosses the glomerular membrane, increasing the
osmolarity of the glomerular filtrate. It induces the
movement of intracellular water into the extra-cellular and vascular spaces (MIMS, 1995).
Patients who are at the more severe end of the
disease spectrum and who are treated during the
acute phase of the illness are the most likely to
benefit from mannitol treatment (Ruff and Lewis,
1994). Intravenous mannitol caused an immediate
resolution of most symptoms in 24 patients, in a
study reported by Palafox et al. (1988).
Benoit et al. (1996) demonstrated that CTX-1B,
by modifying Na 1 current, increased intracellular
Na 1 concentration, which caused water influx and
nodal swelling; and that mannitol, through its osmotic action, reversed this effect by reducing Na 1
entry and increasing the efflux of water. Using
confocal laser scanning microscopy and conventional
current- and voltage-clamp techniques on frog nodes
of Ranvier, they found that CTX-1B (10 nM) caused
an increase in nodal volume and induced high-frequency action potential discharges up to 70–100 Hz.
Increasing the osmolality of the external solution by
about 50% with mannitol restored the nodal volume
to normal and suppressed spontaneous action potentials.
Different results were obtained when the ability of
mannitol to reverse the neurological signs of ciguatera was assessed in rats and mice in vivo. Recordings collected following infusion of mannitol 3 h
after ciguatoxin showed that mannitol did not reverse
the effects of ciguatoxin on nerve conduction in any
of the parameters measured (absolute and relative
refractory periods, conduction velocity and supernormal response) (Capra, 1995; Purcell et al., 1999). By
contrast, Capra (1995) found that the local anaesthetic lignocaine injected into the peritoneum was
capable of reversing all of the major ciguatoxininduced changes in nerve conduction parameters.
Mannitol also failed to protect mice from the lethal
effects of ciguatoxins (Lewis et al., 1993b).
2.7. Detection of toxins in fish
Since ciguatoxins are odourless, tasteless and
generally undetectable by any simple chemical test,
diagnosis of ciguateric fish has been, and still
remains, a significant problem. Oral feeding of
suspect fish to cats or mongoose is a simple and
relatively sensitive assay, but is inhumane, timeconsuming and not suitable for routine monitoring. A
mouse bioassay is frequently used, but this procedure
is also inhumane and requires partial purification of
fish extracts before injection, which is costly and
time consuming. An alternative to the use of mice is
the mosquito bioassay, which was used to obtain a
dose–response relationship between ingested
ciguatoxin and clinical symptoms in humans (Bagnis
et al., 1987). This assay correlates reasonably well
with cat and mouse bioassays (Park, 1994). Many
other assays have been developed using chickens,
brine shrimp and guinea pig atrium, but these
bioassays have one common disadvantage: the lack
of specificity for individual toxins.
Recent studies have focused on the development
of chromatographic methods (HPLC / MS) and immunoassays for the detection of ciguatoxins. The
latter have shown promise for use in seafood safetymonitoring programs. Historically, attempts to validate methods used to measure ciguatera toxicity
have been plagued by a lack of specificity and
adequate reference standards. These problems are
being addressed, and low-cost immunological test
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
kits are now being developed with increasing levels
of precision and accuracy. However, until specificity,
sensitivity and cost-effectiveness are at a high
enough level to monitor individual fish in the
marketplace, these kits will have a small market.
2.7.1. Mouse bioassay
A validated mouse bioassay, based on a method
described by Banner et al. (1960), is still the most
widely used assay for the detection of ciguatoxins in
fish. Based on signs elicited following intraperitoneal
injection of a 20-mg ether extract from fish muscle,
the bioassay includes, but is not limited to, signs of
inactivity, diarrhoea, laboured breathing, cyanosis,
piloerection, tremors, paralysis and staggering gait.
Mice are observed for up to 48 h, and time to death
is recorded. Details of the mouse bioassay are given
in IOC Manuals and Guides (Lewis, 1995). For the
mix of ciguatoxins typically found in Pacific carnivorous fish, the relationship between dose and time
to death is approximated by the equation:
log MU 5 2.3 log(1 1 1 /T )
where MU is number of mouse units of ciguatoxin
injected and T is time to death in hours (Lewis et al.,
1992). One MU is the LD 50 dose for a 20-g mouse,
which is equivalent to 5 ng P-CTX-1, making it one
of the most potent marine toxins known (Lewis et
al., 1991).
When the assay was validated using spiked samples for the detection of ciguatoxins in a 20-mg ether
extract from fish muscle, 63614% of spiked
ciguatoxin was recovered with the standard extraction procedure (Lewis and Sellin, 1993). For ether
extracts containing less than a minimum lethal dose
of CTX (0.4–1.0 MU) in a 20-mg portion, bioassay
signs indicative of the presence of ciguatoxin included rectal temperatures below 338C as well as, at
least, severe diarrhoea or hypersalivation or lachrymation (Lewis et al., 1993b). Using these criteria,
71% of fish confirmed to be implicated in cases of
ciguatera in Queensland (n534) contained levels of
ciguatoxin in standard extracts that were detectable
by mouse bioassay. Except for extracts from the least
toxic of ciguateric fish (0.1–0.5 nmol CTX-1 / kg
fish), signs in mice of intoxication by ciguatoxin
could be distinguished from the toxic reaction that
follows administration of CTX-free ether extracts.
103
The mouse bioassay of ether extracts of fish tissue
is reliable in characterising and quantifying the
presence of ciguatoxin, but requires that the signs of
intoxication in mice are consistent with ciguatoxin.
Unfortunately, the mouse bioassay of 20 mg of an
ether extract cannot detect the presence of ciguatoxins in low-toxicity ciguateric fish. For accurate
quantification of dose, a specific dose versus time-todeath relationship should be established using mice
from a locally available breeding colony (Lewis,
1995).
2.7.2. Immunoassays
Several approaches are available for incorporating
antibodies (or similar proteins) into an assay format
for detecting haptens such as ciguatoxin. In all cases,
the label (a radioisotope, enzyme, or luminescent
fluorescent probe) is used to detect the targeted
compound. Each approach has strengths and weaknesses, but all require a high-affinity antibody that is
selective and specific for the targeted hapten. The
indirect hapten assay requires that the targeted
hapten (ciguatoxin) is first non-selectively immobilised to a solid support prior to its detection with a
labelled antibody specific for the part of the hapten
left exposed following binding. Tests developed by
Hokama and his colleagues (see below) have used
this approach (Lewis, 1994b).
Early immunoassays employed a polyclonal antibody raised to ciguatoxin in sheep. Hokama et al.
(1977) first detected ciguatoxin directly from
ciguateric fish tissues by radioimmunoassay (RIA)
using a sheep antibody prepared against purified
moray eel ciguatoxin conjugated to human serum
albumin as carrier. The sheep antibody was then
purified and coupled to 125 I label to be used in the
RIA. Although the RIA was effective in screening
fish in Hawaii from 1979 to 1981, its complexity,
cost and cross-reactivity with other polyether compounds such as brevetoxin and okadaic acid encouraged the search for an alternative (Juranovic and
Park, 1991).
In 1984, the RIA was replaced by an enzymelinked immunosorbent assay (ELISA), with sheep
anti-ciguatoxin coupled to horseradish peroxidase.
Although cheaper than RIA, the method was tedious
and reactions occurred with other polyether compounds, so it was abandoned (Hokama et al., 1998).
In 1985, Hokama and his colleagues used enzyme-
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labelled polyclonal antibody in a simple ‘stick test’
(S-EIA) (Hokama et al., 1985). Test results showed
false positives, although false negatives were not
reported (Juranovic and Park, 1991). However, up to
six tests per fish were required for accurate determination of ciguateric fish that tested close to
borderline level (Lewis, 1994a).
All subsequent tests have been based on monoclonal antibody (MAb), which has the advantage of
being more specific and available in continuous
supply. In 1989, Hokama and his colleagues used an
IgG MAb to ciguatoxin in a stick enzyme immunoassay. (The assay was based on the ability of sticks
dipped into an alcohol-based fluid to extract and
immobilise ciguatoxin prior to detection with labelled antibody.) They found that 98% of fish
implicated in ciguatera (50 / 51) tested positive. This
method was used extensively for surveys in
ciguatera-endemic areas and for clinical confirmation
of documented fish poisoning for the State of Hawaii
Department of Health (Hokama et al., 1998).
The MAb to ciguatoxin used in these studies was
assessed for cross-reactivity to other polyether toxins. The assay employing the antibody raised to
ciguatoxin detected similar concentrations of pure
ciguatoxin, okadaic acid and a synthesised fragment
of okadaic acid. The cross-reactivity of an antibody
to ciguatoxin and okadaic acid was evidently the
result of a somewhat similar structure. It was surprising that a MAb obtained specifically to okadaic acid
was less sensitive at detecting okadaic acid than the
ciguatoxin antibody. Addition of pure ciguatoxin and
okadaic acid to a ciguatoxin antibody inhibited the
subsequent bonding of this antibody to sticks coated
with an extract from a fish implicated in ciguatera.
This suggests that these polyether toxins compete at
a specific saturable site on the IgG (Lewis, 1994a).
In 1990, Hokama reported a further simplified
solid-phase immunobead assay (SPIA, ‘Ciguatect’,
developed by SIRA Testing Systems in Pasadena,
California) for the screening of toxic fish in the
marketplace. A white, membrane-covered ‘dip stick’
is exposed to the muscle of fish suspected of
containing ciguatoxin. The dipstick is then immersed
in a solution of blue latex beads, which are bound to
MAb specific for ciguatoxin. If the suspect fish
contains ciguatoxin, the toxin will first bind to the
membrane on the dipstick and then to the MAb
bound to the blue latex beads. The white dipstick
will turn blue.
Ciguatect was promoted as being more sensitive
than stick assays and more amenable to field application (Park et al., 1992), but was surrounded by
controversy (Spalding, 1995). It did not compare
favourably when tested against the mouse bioassay
(Dickey et al., 1994). Fifty finfish specimens from
ciguatera-endemic waters of the US Virgin Islands
were assayed using Ciguatect, with three different
methods of tissue sampling: single exposure; triple
exposure; and single exposure to solvent extract from
fish flesh. The mouse bioassay found 33 fish contained ciguatoxin and 17 did not. Positive matches
for the three methods against mouse bioassay were
58, 85 and 94%, respectively. Negative matches
were 17, 22 and 12%, respectively. These results,
which, on the single exposure, incorrectly assayed 28
fish, claiming that 15 fish contained ciguatoxins
when they did not, and 14 did not contain ciguatoxin
when they did, would indicate that false-negative and
-positive values in market situations with Caribbean
fish would be high. However, this result was criticised (perhaps unfairly) on the grounds that the
standard mouse assay was used incorrectly (Spalding, 1995).
In 1998, Hokama et al. reported the development
of a further refinement, the membrane immunobead
assay (MIA). It is based on the same principles as
the SPIA, using a MAb to purified moray eel
ciguatoxin (P-CTX-1), coloured polystyrene beads,
and a hydrophobic membrane laminated onto a solidphase plastic support. The polyether toxins bind to
the hydrophobic membrane and are detected by the
MAb-CTX coated onto the coloured polystyrene
beads. The intensity of the colour on the membrane
relates to the concentration of the toxin. The authors
suggested that variability caused by non-specific
binding of immunobeads to the membrane is minimised by the use of the hydrophobic membrane. The
sensitivity achieved with a small number of toxic
samples was 92.3%, and the specificity for unknown
reef fish was 85.7%. The figure for specificity means
that 14.3% of routinely tested reef fish yield positive
results for ciguatoxin. These values are claimed to be
within acceptable ranges for a biological test system
and compare with the sensitivities and specificities of
older procedures (RIA, S-EIA and SPIA), which
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
ranged from 95.6 to 97.2% and close to 50%,
respectively. Recently, antibodies were produced to
fragments of P-CTX-1 that may have potential in a
simple format assay (Pauillac et al., 2000).
Oceanit Test Systems (Hawaii, USA), is currently
marketing Cigua-Check, a ciguatoxin test kit that is
designed to test rice-grain sizes of fish flesh. The
product is based on the MIA for P-CTX-1 (Hokama
et al., 1998). Cigua-Check is claimed to be most
sensitive, being able to detect ciguatoxin at concentrations that cause clinical symptoms in humans
($0.08 mg / kg fish). Ciguatoxin is not detected by
Cigua-Check at levels of ,0.05 mg / kg. Therefore,
fish that are considered non-toxic by Cigua-Check
may contain ciguatoxin and contribute to cumulative
effects, although such effects appear to be relatively
uncommon.
A problem with immunoassays, which detect
ciguatoxin based on its structure, is that low-potency
ciguatoxins formed from biotransformation of the
main ciguatoxins may cross-react with antibodies to
P-CTX-1, thereby increasing the probability of obtaining false-positive results. This arises because
antibody-based assay response depends on the relative affinity (specificity) of the antibody for each
form of the toxin in a way that may only by chance
be related to the potency of the different forms.
Non-selective binding of ciguatoxin to IgG and nonselective binding of IgG to fish tissue may present
additional obstacles to the development of a successful screening assay for ciguateric fish (Lewis,
1994a). Lewis et al. (1998) suggested that detection
methods being developed based on antibodies raised
against P-CTX-1 or P-CTX-1 fragments may not be
suitable for detecting the Caribbean ciguatoxins.
Another problem is that P-CTX-1 in carrier fish
represents .90% of the toxins present, while CCTX-1 in carrier fish represents only about 50% of
total toxins present.
While lack of sensitivity (i.e., false-negatives) can
be overcome by the testing of more samples from a
population as long as the fish can be tracked to a
locality, lack of specificity (false-positives) is more
difficult to deal with. In the case of a positive result,
it can be overcome by using the rapid test in
conjunction with a more sensitive laboratory-based
test. Confirmatory results could be expected within
24 h using a chemical assay. These comments on
105
sampling strategies are applicable to any test, not just
Cigua-Check (Rawlin and Herfort, 1999).
Incomplete sensitivity and specificity of the immunoassays makes them inappropriate for diagnostic
use in humans with ciguatera (Ting et al., 1998).
2.7.3. Cell-based assays
Several other research groups are developing
assays that detect ciguatoxins by toxic activity rather
than structure. These cell-based assays are far more
likely than antibody-based assays to reflect the
combined potency of a mixture of related toxins
(Spalding, 1995). Thus the high-affinity binding of
ciguatoxins to voltage-sensitive Na 1 channels may
be used in the future as the basis for a sensitive assay
for ciguateric fish. Ciguatoxins bind quasi-irreversibly to site 5 on Na 1 channels, a site overlapping
the brevetoxin binding site, and selectively inhibit
the binding of [ 3 H]brevetoxin to Na 1 channels in rat
brain synaptosomes (Lombet et al., 1987; Lewis et
al., 1991).
Manger et al. (1995, 1997) reported a cell-based
assay for detecting ciguatoxins. It uses cultured
mouse neuroblastoma cells that contain the tetrazolium compound MTT, which is reduced by healthy, but not dead, cells to a blue-coloured formazan
product. Fish samples containing ciguatoxins do not
cause the assay cells to change colour, since
ciguatoxins bind to the sodium (Na 1 ) channel
receptors on the cells, which are damaged and
prevented from reducing MTT. Purified P-CTX-1
and P-CTX-3 produced ID 50 values (inhibitory dose
that reduced cell viability to 50% of ouabain / veratridine-treated controls) at 7 h of about 1 and 3 pg,
respectively. Longer incubation resulted in enhanced
assay sensitivity, as exhibited by the 22-h CTX-1
ID 50 value of ,0.25 pg. These are much smaller
amounts than mouse bioassays can detect, and cell
bioassays correlate well with mouse bioassays. Analysis of ciguatoxins takes as little as 4 h by cell
bioassay, compared with 48 h for mouse bioassay.
Manger et al. (1997) examined finfish extracts
characterised as ciguatoxic by mouse bioassay, and
purified ciguatoxin standards, to determine the extent
of correlation between cell and mouse bioassays. The
most potent of the extracts, with an ID 50 of about
0.125 mg by cell assay and a mouse death time of 0.1
h, was obtained from a fish implicated in ciguatera.
106
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
An extract that was less potent by mouse bioassay
(4.7 h survival) was also comparatively less potent in
cell bioassay, with an ID 50 value of approximately 2
mg. Two extracts that were non-lethal in mice were
also devoid of activity in cell bioassay. Purified
standards also showed good correlation.
Although such cell-based assays are sensitive and
related to toxin potency, the problem is to make
them cost effective for the routine screening of
individual fish. If this becomes a possibility, the
ability of the cell-based assay to detect such low
levels of ciguatoxic activity raises the potential of
imposing regulatory limits for ciguatoxins in fish.
This would pose a further problem — it is unknown
whether low levels of ciguatoxins in a large number
of fish pose a significant risk of chronic toxicity.
backup for mouse bioassay and immunoassay screening.
3. Dose–response assessment
This section deals with the incidence of ciguatera;
the prevalence of ciguateric fish; fish characteristics
that affect the clinical response; concentrations of
ciguatoxin(s) in ciguateric fish and the toxic dose; the
effect of geographical location on the clinical response; and human susceptibility, including the
cumulative nature of toxicity and morbidity and
mortality rates.
3.1. Incidence of ciguatera
2.7.4. Chemical analyses
The ciguatoxins do not possess a useful chromophore for selective spectroscopic detection, but contain a relatively reactive primary hydroxyl group to
which a label can be attached (after appropriate clean
up) prior to detection. Detectors (e.g., fluorescence or
ion spray mass spectrometry) coupled to optimised
HPLC have been used for analytical detection of
derived ciguatoxins in crude extracts of fish (Lewis
and Sellin, 1992, 1993). Although time consuming,
this procedure is useful to validate responses obtained by rapid screening assays.
In a recent paper, Lewis et al. (1999) reported a
new procedure for ciguatoxin analysis based on
gradient reversed-phase HPLC / tandem mass spectrometry (HPLC / MS / MS). The method gave a
linear response to pure Pacific and Caribbean
ciguatoxins (P-CTX-1 and C-CTX-1) and the structurally related brevetoxin (PbTx-2) spiked into crude
extracts of fish. Levels equivalent to 40 ppt P-CXT1, 100 ppt C-CTX-1 and 200 ppt PbTx-2 were
detectable in fish muscle. Using P-CTX-1 as an
internal standard, the analysis of extracts of 30
ciguateric fish from the Caribbean (eight toxic, 12
borderline and 10 non-toxic by mouse bioassay)
confirmed the reliability of the method and allowed
an estimated risk level of 0.25 ppb (0.25 mg / kg)
C-CTX-1 to be established. Thus HPLC / MS / MS
provides a sensitive analytical method for the determination of Pacific and Caribbean ciguatoxins at
sub-ppb levels in fish muscle, and an accurate
Ciguatera is the most common foodborne illness
related to finfish consumption (Lange, 1994). It is
endemic throughout the Caribbean and tropical and
subtropical Indo-Pacific regions, and there tends to
be an increase in incidence with decreasing latitude
(Juranovic and Park, 1991). In 1984, Ragelis suggested that 10 000–50 000 people who live in or
visit tropical and subtropical areas may suffer from
ciguatera each year. Ruff and Lewis (1994) estimated .25 000 people are affected annually; and
Brusle´ (1997) estimated 10 000–50 000.
With increased utilisation of tropical reef fish
through trade and travel, incidents of ciguatera are
increasing, although many probably go unreported
(Juranovic and Park, 1991; Ruff and Lewis, 1994).
Because the disease is not reportable to public health
authorities either nationally or internationally, its
incidence is not clearly known and its epidemiology
is not clearly understood (Lange et al., 1992).
Reasons for under-reporting include non-reporting of
confirmed cases and misdiagnosis, with mild cases
often mistaken for more common illnesses (Swift
and Swift, 1993; Ruff and Lewis, 1994; Lewis and
King, 1996; Fenner et al., 1997). Ting et al. (1998)
reported that many cases are undiagnosed until after
secondary or even tertiary referral, and that it is
inescapable that many cases, especially sporadic
cases not involved in a mini-epidemic, remain undiagnosed.
Ragelis (1984) estimated there were more than
2000 cases of ciguatera in the US each year, and
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
Lipp and Rose (1997) ranked ciguatoxin (19%)
second to scombroid toxin (57%) in the list of
aetiological agents of reported outbreaks of seafoodborne disease associated with fish in the US, 1983–
92. Approximately 90% of cases reported to the
Center for Disease Control (CDC; Atlanta, GA),
occur in Florida and Hawaii. Few reports get to the
CDC from areas where ciguatera is ‘hyperendemic’,
such as Puerto Rico, the US Virgin Islands and
American Samoa (Lange et al., 1992).
Gollop and Pon (1992) reported 150 incidents
involving 462 people for an annual average rate of
0.87 cases / 10 000 population in the State of Hawaii
in the 5-year period from January 1984 to December
1988. There were 652 people who were exposed,
making an overall attack rate of 71%. However, the
attack rate varied with each outbreak, sometimes
reaching 100%. The island of Hawaii reported the
most incidents, followed by Oahu, Kauai and Maui,
respectively. Gollop and Pon (1992) pointed out that
the number of incidents, rather than the number of
cases, correlates more closely with the actual endemicity of ciguatera at a given time. The number of
cases relates to the number of people who ate toxic
fish. A single outbreak affecting 100 people would
be of less epidemiological consequence than 100
different fish making 100 people ill.
In Miami, Florida, voluntary reports to the Public
Health Department estimated an average annual
incidence of at least five cases / 10 000 persons (i.e.,
900 cases / year) (Lawrence et al., 1980). This compared with annual incidences of 30 / 10 000 on Iles
Saintes, Guadeloupe, and 73 / 10 000 on the US
Virgin Islands in the Caribbean (Ruff and Lewis,
1994).
Todd (1997) reported 15 outbreaks of ciguatera in
Canada from 1983 to 1997. Fifty-three people were
affected, and barracuda was the fish involved in
seven of the outbreaks. He stated that ciguatera is
probably considerably under-reported in Canada, and
estimated that about 300 cases occur annually.
Quod and Turquet (1996) reported 159 outbreaks
of icthyosarcotoxism, involving 477 people, between
´
1986 and 1994 on the Island of Reunion
(southwestern Indian Ocean). Ciguatera represented 78.6%
of total cases and its annual incidence rate was
estimated at 0.78 / 10 000 residents. The other forms
of icthyosarcotoxism were scombroid poisoning,
15.5%; hallucinatory poisoning alone, 3.5%; tet-
107
rodotoxism, 0.2%; and undetermined poisoning,
2.1%.
Around a thousand cases of ciguatera have been
notified to public health monitoring bodies in Australia (Gillespie et al., 1986; Broadbent, 1987) and
the annual incidence in coastal areas of Queensland
is similar to the 3.6 / 10 000 average reported for the
South Pacific region by Yasumoto et al. (1984).
Cases occur annually along the tropical coast of
eastern Australia. Tonge et al. (1967) reported two
outbreaks, and another case of a death attributed to
ciguatera, in Queensland, all caused by the consumption of mackerel. Major and minor outbreaks have
occurred in Sydney, New South Wales, Australia,
over the past 15 years (Capra and Cameron, 1991;
Capra, 1997; Karalis et al., 2000). Most have been
caused by the consumption of Spanish mackerel or
reef fish from Queensland.
For countries of the South Pacific, the highest
average incidence of reported ciguatera for the
period 1985–1990 was about 100 cases / 10 000
population / year in Kiribati, Tokelau and Tuvalu
(Lewis, 1992b). In French Polynesia, Vanuatu, and
the Marshall and Cook Islands, the average reported
incidence was less than half these levels. The
remaining 13 countries reported fewer than 15 cases /
10 000 people / year. Over the same period, the
average annual reported incidence in Queensland
(population 2.9 million) was similar to that of Tonga
(0.16 cases per 10 000 population). However, the
figures for Queensland are thought to represent only
about 20% of actual cases (Lewis, 1992b).
Most authors have reported that the incidence of
ciguatera is not seasonal (Randall, 1958; Halstead,
1978; Tonge et al., 1967; Juranovic and Park, 1991),
and outbreaks recorded in Australia show no seasonal pattern. Legrand and Bagnis (1991) described
three epidemiological patterns in the Pacific: endemic areas, where cases are observed all year
around; epidemic areas, where outbreaks only are
observed; and intermediate areas, where outbreaks
occur, but cases are also observed between outbreaks. On the other hand, Oreihaka (1992) reported
that ciguatera is seasonal (and infrequent) in the
Solomon Islands (north-western Pacific), and islanders, through traditional knowledge, avoid consumption of fish considered ciguatoxic during these
periods. Outbreaks in Fiji are also seasonal, increasing in spring and reaching a maximum in November
108
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
(Lewis, 1992b). Sours and Smith (1980) of the US
CDC report that, of outbreaks of ciguatera occurring
in the US between 1972 and 1978, ‘‘outbreaks in
Florida tended to take place slightly later in the
spring than those in Hawaii’’. Halstead (1978)
suggested that the spawning season in some of the
large predacious fishes might be a more dangerous
period than other seasons of the year.
3.2. Fish characteristics that affect clinical
response
There are major difficulties in defining the prevalence of ciguateric fish, because of sporadic and
patchy occurrence of toxic G. toxicus. Prevalence
must be defined in terms of the species and the
particular fish population. In discussing the prevalence of ciguateric fish, this should be done on the
basis of a specific fish population on a particular
reef, or in a particular bay. Even the latter has
difficulties, as ciguateric fish may move from reef to
reef or be pelagic.
Ingestion of ciguateric herbivorous fish causes
mostly digestive and neurological symptoms, while
ingestion of ciguateric carnivorous fish causes a
broader range of symptoms, including more cardiovascular effects (Bagnis and Legrand, 1987;
Kodama and Hokama, 1989). This is largely the
result of different ciguatoxins being present in
different species. Carnivorous fish are generally
considered to be the most toxic (Glaziou and Martin,
1992).
Vernoux et al. (1985) extracted ciguatoxins from
36 poisonous fish, including nine dangerous species,
collected in the Caribbean and carried out toxicity
assays in mice. They found that the ratios of toxin
concentrations in the liver or other viscera to that of
muscle were high and varied with the species,
suggesting that the ciguatoxin is stored in different
ways in different fish. Using mouse assays, Vernoux
et al. (1985) found ciguatoxins in the blood, muscle,
gonads, gills, heart, skin and bones of fish. Concentrations were highest in the viscera and in particular in the liver, kidney and spleen. Subcellular
fractionation of hepatocytes revealed that most
ciguatoxin was attached to cytoplasmic proteins and
that some toxin was probably bound to membranes.
Helfrich et al. (1968) estimated that the amount of
ciguatoxin per unit of tissue weight is 50 times
greater in fish liver than in muscle.
There is an increase in the percentage of toxic fish
within a species with size (weight). This is because
older fish have had a longer period of consuming
toxic prey and accumulating high concentrations of
ciguatoxins in their tissues. However, on occasions,
slow excretion of ciguatoxins without additional
intake may cause larger fish to decrease in toxicity.
While there is no scientific evidence to support a
2.5-kg ‘safety limit’ for coral trout, some restaurants /
retailers in Australia will not accept large fish in an
attempt to avoid ciguatera.
3.3. Concentration of ciguatoxin(s) in ciguateric
fish, and toxic dose
Most cases of ciguatera in the Pacific involve
consumption of the flesh of ciguateric fish that
contains the equivalent of 0.1–5 nmol P-CTX-1 / kg
(Lewis, 1992a; Lewis and Sellin, 1992, 1993), which
is equivalent to about 0.1–5 mg / kg. The severity and
duration of symptoms are to some extent dose
dependent, but this is complicated by accumulation
of ciguatoxins in the human body. Another complication is the possibility that symptoms may result
from the combined action of more than one type of
toxin (Schatz, 1989; Whittle and Gallacher, 2000).
In an outbreak of ciguatera in an Australian family
described by Fenner et al. (1997), symptom severity
and duration appeared to be dose dependent. The
presence of ciguatoxins in the suspect fish (coral
trout) was confirmed by bioassay in mice. The
father, who ate about 1 kg of the fish, suffered the
most severe, long-lasting gastrointestinal and neurological symptoms, and the children, who ate only
small pieces, suffered mainly short-lived gastrointestinal symptoms. The mother, who ate about 0.5
kg, experienced severe gastrointestinal symptoms
initially, and a slight burning sensation of the hands
and mouth and mild pruritus in subsequent days. The
concentration of P-CTX-1 in the coral trout was
calculated as 0.25 MU / g muscle, or 1.3 mg / kg
muscle, a relatively high level and consistent with
the severe poisoning seen in the adults. As the man
ate about 1 kg of fish, his total intake of P-CTX-1
would have been about 1.3 mg. The woman ate about
500 g of fish, so her total intake would have been
about 0.65 mg.
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
As mild ciguatera has been associated with the
consumption of fish containing as little as 0.1 mg / kg
CTX-1, the lowest dose of P-CTX-1 that might be
expected to be toxic in adult would be about 0.05 mg
of toxin, or 0.001 mg / kg bodyweight (assuming
consumption of 500 g of fish containing 0.1 mg / kg
CTX-1 by a 50-kg individual). This dose might
cause about two people out of 10 to be sick. Ten
times this dose (0.5 mg, or 0.01 mg / kg in a 50-kg
person) would be expected to be toxic in most
people, and easily obtained from an average serving
of 300 g of some ciguateric fish (Lehane, 2000).
If risk factors are applied to the concentration of
0.1 mg / kg P-CTX-1 in a fish that is likely to be toxic
(say 32 for individual variation, 32 for quantity
consumed, and 32 for possible problems with the
assay due to difficulties detecting such low levels), a
‘safe’ fish would contain no more than about 0.01
mg / kg P-CTX-1 (Lehane, 2000).
3.4. Geographical location and the clinical
response
The diagnosis of ciguatera depends on clinical
criteria, and paraesthesia is considered the clinical
hallmark of the disease (Bagnis et al., 1979). Clinical
descriptions vary from one country to another. For
example, in the US Virgin Islands, gastrointestinal
tract symptoms (91% of patients) were more common than paraesthesia (54% of patients) (Morris et
al., 1982), compared with 73 and 93%, respectively,
in French Polynesia (Glaziou and Martin, 1992). It
has also been reported that the sequence of symptom
onset has geographic differences: in the South
Pacific, neurological symptoms precede gastrointestinal symptoms, while in the West Indies the reverse is
true (Rodgers and Muench, 1986). These differences
are most likely related to the nature of the ciguatoxins present in ciguateric fish in these different
geographical areas. A third class of ciguatoxins is
likely to explain the different symptoms observed in
the Indian Ocean (Lewis and Hurbungs, unpublished
results). Here fish can accumulate lethal levels of
toxin (Habermehl et al., 1994) and produce symptoms reminiscent of hallucinatory poisoning, including lack of coordination, loss of equilibrium, hallucinations, mental depression and nightmares (Quod
and Turquet, 1996).
109
3.5. Human susceptibility, and morbidity and
mortality rates
Human factors that influence the reported severity
and duration of symptoms of ciguatera include
subjective descriptions, ethnic group, age, sex, individual patient variation (including that associated
with cumulative toxicity) and the route of poisoning
(e.g., oral, or via the placenta or milk, or sexual
intercourse).
Symptom patterns differ among ethnic groups and
between the sexes. In the Pacific, men are more
likely to experience diarrhoea and abdominal pain,
whereas women more often report arthralgia and
myalgia (Sanders, 1987). In Vanuatu, Melanesians
with ciguatera are said to be prone to pruritus,
incoordination, abdominal pain and weakness,
whereas Europeans are more likely to have watery
eyes, neck stiffness, joint pains and temperature
dysaesthesia, and Chinese tend to have diarrhoea and
abdominal pain. Whether the variation in symptoms
is a result of genetic predisposition or different
eating preferences is not clear (Lange, 1987).
In the 3009 cases of ciguatera in the South Pacific
described by Bagnis et al. (1979), the youngest
patient was aged 1 year and the oldest 82 years.
Fifty-nine percent of patients were male and 41%
female, and almost 50% of the patients were in their
second or third decade of life. Significant differences
in symptoms were also noted between Melanesian
and Polynesian ethnic groups (Bagnis et al., 1979).
Because the severity of the disease is often quite
variable, Lange (1993) developed symptom checklist
rating scales for epidemiological investigations used
for quantifying illness severity and selectively monitoring response to therapy in patients with chronic
toxicity. Glaziou and Martin (1992) also used a
checklist when they studied the medical records of
ciguatera in French Polynesia over a 1-year period
(1991) in order to determine the factors that influence the clinical response. Of the 551 cases
notified (27.6 / 10 000 population), the mean age was
36.6 years (S.D.615.6). The largest group was 30–
39-year-olds (138 cases, or 97 / 10 000). The
male:female ratio was 1.6:1. A clinical score was
calculated to assess the outcome for each case. The
adjusted odds ratio (OR) for severe disease (33.2%
with a score .5) was significantly increased when
the fish ingested were carnivorous (OR51.62) and
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L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
when there was a history of a previous attack (OR5
1.71).
Glaziou and Legrand (1994) also noted an association between age and illness, saying that 30–49year-olds are most affected and children appear to be
less susceptible. However, even breast-fed infants are
at risk of contracting the disease (Bagnis and Legrand, 1987; Blythe and De Sylva, 1990; Karalis et
al., 2000), and ciguatoxins pass to the embryo / fetus
in utero, and to partners during sexual intercourse
(see Ruff and Lewis, 1994).
While the cumulative nature of ciguatoxin affects
host–toxin interaction, it is difficult to predict to
what extent a person has accumulated ciguatoxins,
particularly if he / she lives in an endemic area.
Repeated meals of fish containing ciguatoxins, but
not in amounts high enough to cause acute disease,
may eventually lead to the development of symptoms. Accumulation of ciguatoxins in the body
makes the calculations for toxic dose rather academic. At present there is no way of knowing what dose
of ciguatoxins a person may have accumulated, and
how close he / she is to the symptom threshold.
The severity of ciguatera thus varies according to
the amount of toxin ingested and individual susceptibility. The time to onset of symptoms and the
symptoms themselves are highly variable, even
between persons who have consumed the same fish.
In general, neurological symptoms last about 6
weeks and complete recovery may be expected, but
sometimes this takes weeks, months or years
(Juranovic and Park, 1991). Subsequent episodes of
poisoning tend to be more severe than the first,
because the toxin is cumulative in the human body
(Glaziou and Legrand, 1994). The effect of the toxin
thus appears to be dose related (Juranovic and Park,
1991).
Exceptionally severe poisoning can lead to
paralysis, coma (DeFusco et al., 1993) and death.
While ciguatera rarely causes death, the mortality
rates have been as high as 12 and 20% in severe
outbreaks (Lange, 1987; Habermehl et al., 1994).
More typically, there were only three deaths among
the 3009 cases examined in French Polynesia by
Bagnis et al. (1979), a mortality rate of 0.1%. The
highest mortality rate attributed to ciguatera (20%)
was from the east coast of Madagascar (Habermehl
et al., 1994). Five hundred people, 98 of whom died,
were poisoned by eating the flesh of a shark (Carcharhinus amboinensis).
4. Exposure assessment
The exposure assessment to ciguatoxins will examine, in so far as is possible, genetic and natural
and man-made environmental factors that affect
amounts and distribution of the dinoflagellates and
the toxins they produce, population demographics,
and future exposure trends.
4.1. Factors affecting amounts and distribution of
ciguatoxins produced
4.1.1. Bleaching and death of coral
Yasumoto et al. (1980) pointed out that that dead
coral surfaces covered with filamentous or calcareous
macroalgae provide a favourable environment for the
proliferation of ciguateric G. toxicus. Lewis (1986a)
reported that G. toxicus grows prodigiously following both natural and man-made disturbances of coral
reefs. This is presumably because increased amounts
of dead coral act as substrate for macroalgal hosts of
the dinoflagellate. Such events have sometimes been
shown to stimulate an increase in production of
´
ciguatoxin (Ruff, 1989; De Sylva, 1994; Brusle,
1997).
Worldwide coral reef bleaching is now well
documented and seems to indicate extreme stress in
coral colonies caused by increased water temperature, pollution, sedimentation or changes in salinity.
This is a process in which coral polyps spontaneously expel the symbiotic algae that give them their
colourful hues. Coral bleaching has been related to a
rise of only 18C above average summer sea-surface
temperatures. Extremely warm waters and unprecedented coral bleaching were reported throughout
the tropical areas of the Southern Hemisphere during
the first half of 1998. When the waters cooled in the
second half of the year, the corals had either
recovered or died off. Fifty countries have reported
the phenomenon since 1997 (NOAA, 1999).
An international team of scientists has recently
proposed that global warming may have another
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
effect on ocean water and coral (Kleypas et al.,
1999). The scientists have suggested that increasing
levels of carbon dioxide in the atmosphere mix with
the surface ocean and create more acidic seawater.
This decreases the level of carbonate in the water,
making it difficult for coral to create or maintain
skeletal structure. The coral structure weakens, and
can crumble more easily when faced with natural
erosion or structural attack, thus hastening the damage caused by storms and increased tourism, for
example.
Disturbance of coral reef environments by natural
events such as storms, heavy rains, earthquakes and
tidal waves may precipitate outbreaks of ciguatera
(WHO, 1981; Ruff, 1989; Juranovic and Park,
1991). Toxic fish are often found on the windward
side of tropical islands, where wave energy and
storm damage to reef systems is greatest (Ruff,
1989).
There are many documented instances of natural
activities adversely affecting coral reef ecosystems.
For example, fish caught off the Bahamas following
a severe storm in 1908 were associated with numerous cases. Following the passage of Hurricane David
in the West Indies in 1979 there were several cases,
including two deaths; and following Hurricane Allen’s passage in 1980, Puerto Rico experienced an
outbreak the year after (De Sylva, 1994). On the
other hand, following Hurricane Hugo, one of the
most violent of the century in the Little Antilles,
which passed over Guadeloupe Island in September
1989, no G. toxicus was identified associated with
damaged coral and ciguatera did not occur (see
´ 1997).
Brusle,
Human effects leading to adverse changes in the
reef environment include:
•
•
•
•
•
•
•
•
•
•
collecting of marine animals;
tourism;
fishing and the use of poisons;
underwater or shoreline explosions;
sewage and eutrophication;
petroleum hydrocarbons, heavy metals, and power
plants;
dredging and filling;
construction of docks and piers;
recreational activities;
military activities (Ruff, 1989);
111
• grounding of ships and shipwrecks;
• introduction of ballast waters from elsewhere
(Hallegraeff et al., 1990).
It remains to be seen to what extent widespread
bleaching and death of coral will exacerbate the
problem of ciguatera.
4.1.2. Macroalgal hosts and bacterial associations
of G. toxicus
Shimizu et al. (1982) found the largest populations
of G. toxicus in Hawaii in association with the red
alga Spyridia filamentosa. According to Shirai et al.
(1991), also centred in Hawaii, the main algae on
which G. toxicus grows are (1) Turbinaria sp. (2)
Jania sp. (3) Spyridia sp. (4) Laurencia sp. and (5)
potentially any red, brown or green algae.
Hahn (1991) investigated macroalgal host–dinoflagellate associations at four locations around Heron
Island (Queensland, Australia) and Platypus Bay
(Fraser Island, Queensland, Australia). On Heron
Island, the predominant algae were Chlorodesmis
fastigiata, Turbinaria ornata, Halimeda sp. and
Sargassum sp. G. toxicus was found on all four, but
was in greatest numbers on Sargassum and Turbinaria. In Platypus Bay, Cladophora sp. was predominant.
Some research indicates that certain bacteria are
found symbiotically associated with dinoflagellates
and seem to play a role in the elaboration of toxins
by the symbiont dinoflagellates. Carlson (1984)
found that when bacteria were added to dinoflagellate cultures growth rates and cell yields increased;
and studies on the toxicity of bacterial free and
bacterial contaminated cultures of the toxic dinoflagellate Prorocentrum concavum indicated that bacteria may contribute to variations in toxin production
by dinoflagellates. Carlson (1984) suggested that
bacteria may produce nutrients that are assimilated
by dinoflagellates and are necessary for producing
ciguatoxins, and Juranovic and Park (1991) suggested that bacteria might synthesise the toxins,
which are then phagocytosed by the dinoflagellates.
Bacteria associated with dinoflagellates include
strains of Pseudomonas (most common), Nocardia,
Vibrio, Aeromonas, Flavobacterium and Moraxella
(Tosteson et al., 1989; Gonzales et al., 1992).
112
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
4.1.3. Environmental influences on dinoflagellate
communities and cultures
4.1.3.1. Australian studies
On the Queensland coast, Gillespie et al. (1985)
found G. toxicus (up to 100 / g macroalgae), which
contained appreciable levels of the water-soluble
maitotoxin, but not ciguatoxin. Lewis et al. (1988)
also isolated a non-ciguatoxin-producing strain of G.
toxicus, at Flinders Reef, off southern Queensland. In
culture, G. toxicus may produce maitotoxin, but little
or no ciguatoxin (Bagnis et al., 1980). The dinoflagellate may require specific conditions for the
elaboration of ciguatoxin that are not necessarily the
´ 1997).
same as those required for growth (Brusle,
Holmes et al. (1991) cultured 13 strains of G.
toxicus isolated from Queensland, Hawaii, French
Polynesia and the Virgin Islands and extracted them
for ciguatoxins. They also extracted a biodetrital
sample containing wild G. toxicus collected from
Kiribati. Ciguatoxin, as characterised from moray
eels, was not detected in any of the strains examined.
Only the two Queensland strains and the wild G.
toxicus produced ciguatoxin-precursor gambiertoxins. These were less polar than ciguatoxin and
produced bioassay signs and in vitro responses that
were similar, but not identical, to those produced by
ciguatoxin. The wild cells produced about 100 times
more gambiertoxins / cell than did the two culture
strains (Holmes et al., 1991).
In a second survey, Holmes et al. (1994) sieved
benthic biodetritus samples from unattached green
macroalgae (Cladophora sp.) in Platypus Bay, and
found mean population densities of G. toxicus of
four to 556 cells / g Cladophora. There was considerable variation in the size of G. toxicus populations. A
sample taken in May 1988 had the highest, and one
taken in May 1989 the lowest, densities. There was
no obvious relationship between G. toxicus population densities and seawater temperature and salinity.
Gambiertoxins were detected in one of six samples,
indicating that G. toxicus was likely to be the origin
of the ciguatoxins present in fish in the bay. The
results confirmed that not all strains of G. toxicus
produce gambiertoxins in the wild.
The G. toxicus populations in Platypus Bay are the
second highest reported from Queensland. Higher
populations of 1800 G. toxicus / g substrate have been
measured at Flinders Reef (Gillespie et al., 1985),
but even the Flinders Reef populations were small
compared with those of 4.5310 5 cells / g of macroalgae reported from the Gambier Islands (Bagnis et
al., 1985). Bagnis et al. (1990) found 100-fold
increases in G. toxicus populations can occur in less
than 2 weeks.
On Heron Island, Hahn (1991) found there was a
fairly low dinoflagellate presence (,200 cells / g
substrate) from January 1988 to November 1988,
with an increase in numbers in April and November
1989. He thought the increase in dinoflagellates in
1989 may have been the result of decreased sedimentary material, which had been evident in 1988.
Heron Island is not generally associated with ciguatera, but gambiertoxins and ciguatoxins were found
in algal detritus, and ciguatoxins were found in
gastropods and crabs.
The physical nature of Platypus Bay appears to be
ideal for the growth of Cladophora sp. and G.
toxicus. The Bay is on the protected western side of
Fraser Island. Its marine bottom is devoid of rock
and hard coral, and is flat and featureless. It hosts a
consistent perennial growth of Cladophora sp.,
which forms an almost continual mono-algal turf on
the Bay floor. The Bay is protected from the Hervey
Bay current, which runs along the west coast of
Fraser Island, and the Island protects it from prevailing winds and rough seas. The dense, fine-branching
Cladophora sp. also provides shelter from turbulence. However, strong westerly winds cause rough
conditions, and wash Cladophora sp. onto the leeward beaches of the Bay (Hahn, 1991).
4.1.3.2. Other studies
Carlson (1984) studied dinoflagellate communities
in the British and US Virgin Islands in the Caribbean
over a 12-month period. He examined macroalgae,
sediments, dead coral and water for dinoflagellates at
seven stations, which included coral reefs and
protected inshore bays. Forty-six species were recorded, of which 12 were known or determined to be
toxic. Dinoflagellates were most abundant in association with macroalgae found at depths between 0.5
and 3.0 m. Toxic species averaged 76% of yearly
dinoflagellate biovolume seen during the study.
Prorocentrum mexicanum, G. toxicus and P. concavum were the dominant toxic species at inshore
stations, while Ostreopsis siamensis and Prorocentrum lima were dominant on coral reefs.
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
Carlson (1984) found that G. toxicus was a
dominant toxic species at inshore stations, and that
protected mangrove lagoons supported greater numbers of dinoflagellates than coral reefs. Specific
dinoflagellate–macroalgae associations were noted.
Analysis of water samples revealed higher concentrations of nutrients adjacent to macroalgae than in
open waters. Species responses to other environmental factors were variable, but the combined toxic
species biovolume from four inshore stations was
highly correlated with monthly precipitation. However, Carlson (1984) did not routinely measure toxin
production by the colonies of dinoflagellate species
he monitored.
Yasumoto et al. (1980) found that low salinity and
high light intensities adversely affected G. toxicus
growth and suggested that these factors may influence the distribution of the species. Carlson
(1984) also found that light intensity appeared to
influence benthic dinoflagellate distribution. Macroalgal-associated dinoflagellates at more than 60
sites were not found at depths ,0.5 m, where light
levels reached .6.5310 4 lux. Some shallow, whitesand-bottomed lagoons had large stands of macroalgae, but these species did not support many
dinoflagellates. Besides the light intensity and salinity relationships, Yasumoto et al. (1980) could find no
correlation between the abundance of G. toxicus and
other environmental variables.
In contrast, Carlson (1984) observed several significant correlations between numbers of benthic
dinoflagellates and environmental factors. He collected and analysed water samples directly adjacent
to macroalgae. G. toxicus numbers were negatively
correlated with salinity and temperature (P,0.05)
and positively correlated with all of the nutrient
parameters measured: NO 2 , NO 3 , NH 4 , PO 4 , and
total P (P,0.05). No correlation was observed
between numbers of G. toxicus and pH. The following possible causes of the significant relationship
between the dinoflagellates and rainfall were suggested:
• the influx of nutrients from land run-off;
• elevated bacterial counts seen in protected marine
areas following heavy rains;
• remineralisation of organic constituents in the
water, which would subsequently become available to dinoflagellates or macroalgae;
113
• purging of inhibiting substances accumulated
during periods of low rainfall; and
• increased growth of macroalgae, which could
subsequently influence dinoflagellate growth.
Bomber et al. (1988) studied environmental influences on populations of G. toxicus in the Florida
Keys and in culture. In its natural habitat, the
dinoflagellate preferred depths of 1–4 m, and grew
best at 11% of full sunlight. It reached maximum
abundance when the water temperature was about
308C, in September. Populations were greater than
half-maximum when temperatures were between 27
and 308C. In laboratory unialgal culture experiments,
temperatures of .29 and ,268C limited division
rates, although growth was possible from 19.5 to
348C. Optimal growth occurred at 32% salinity, with
division rates at 25 and 40% salinity only 34 and
57% of maximum, respectively.
The time period required for transmission of
ciguatoxins from dinoflagellates to humans is not
known, but Carlson (1984) said that a lag period of
about 1 month corresponded remarkably well with
peak periods of toxic dinoflagellate abundance he
observed in the Caribbean in his 1-year study.
Consistent with this observation, Bagnis et al. (1990)
found in Tahiti that when a bloom of G. toxicus
occurred on a reef the herbivorous surgeonfish
became toxic very rapidly.
4.1.4. Genetics of dinoflagellates in relation to
toxin production
When Holmes et al. (1991) cultured 14 strains of
G. toxicus, only three produced gambiertoxins.
Changes in nutrient media made from seawater from
Flinders Reef or Platypus Bay did not influence
whether or not strains produced gambiertoxins, or
the amounts produced. However, Holmes and Lewis
(1992) showed that the concentration (or type) of
gambiertoxins produced by cultured clones of G.
toxicus can change during the time they are maintained in culture.
Holmes et al. (1994) proposed the existence of
‘super-producing strains’ of G. toxicus to explain
variation in gambiertoxin production between strains.
Holmes and Lewis (1994) suggested that it is likely
that the conditions that enhance growth will not
necessarily be those that enhance toxin production,
and that future research could focus on the effect of
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L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
different combinations of genetic and environmental
factors on the rate of gambiertoxin production.
4.2. Population demographics
4.2.1. Distribution
Traditionally, ciguatera has been an important
medical entity within a wide circumglobal area,
mainly between the latitudes of 358N and 358S
(Juranovic and Park, 1991). Cases are commonly
encountered in Pacific and Indian Ocean regions and
´ 1997). The disease is a
in the Caribbean (Brusle,
significant health concern to inhabitants of small
island countries in tropical and sub-tropical waters,
especially the smaller island nations of the Pacific
basin. Of these, the atoll island countries are the
worst affected (Lewis, 1992b). Although the South
Pacific Epidemiological and Health Information Service (SPEHIS) compiles a valuable fish poisoning
database, ciguatera is invariably under-reported
(Lewis, 1992b). It is common in French Polynesia,
Micronesia, Tokelau, Tuvalu, North Marianna, the
Marshall and Cook Islands, New Caledonia, Kiribati,
Fiji, Tonga, Vanuatu and Samoa (Lewis, 1992b;
´ 1997). An
Glaziou and Legrand, 1994; Brusle,
indication of ciguatera risk associated with locally
caught fish is given in Fig. 2.
In the US, toxicity is usually confined to fish
caught in Hawaii and Florida (Lange, 1987). Cases
have been reported from Louisiana, Massachusetts,
New York, Vermont, District of Columbia, Texas and
Kansas (Barton et al., 1995). Morris et al. (1990)
reported an outbreak of ciguatera caused by fish
(probably barracuda) caught off the coast of North
Carolina. In the Caribbean, the incidence of the
disease is high in St Barthelemy, Puerto Rico and the
Virgin Islands. In contrast, it is a mild problem in
´ 1997).
Cayman Island and Guadeloupe (Brusle,
In Australia, most ciguateric fish are caught in
Queensland and Northern Territory waters. The main
ciguateric areas in Queensland are Maryborough to
Gladstone, especially along the inside coast of Fraser
Island, and Bowen to Port Douglas (Great Barrier
Reef). In the Northern Territory, ciguatera occurs
around the Gove Peninsula (Nhulunbuy) and Groote
Eylandt. Fish from northern New South Wales and
Western Australia rarely, if ever, cause ciguatera
(Lewis and King, 1996).
In Asia and the Indian Ocean, ciguateric fish occur
in tropical and sub-tropical insular areas. Cases have
Fig. 2. Global distribution of ciguatera, with areas of high-to-moderate risk (heavy shading) and low or uncertain risk (lighter shading)
identified.
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
´
been reported from the Reunion
and Rodrigues
Islands, Mauritius, the Seychelles, the Maldives and
Japan. Ciguatera is uncommon in Madagascar, Comores, Sri Lanka and Indonesia (Glaziou and Leg´ 1997).
rand, 1994; Brusle,
4.2.2. At-risk population groups
About 400 million people live in areas where
ciguateric fish are caught. In addition, fish caught in
endemic countries are sent to many parts of the
world by air transport. Consequently, outbreaks may
occur in any population eating ciguateric fish in any
part of the world. The main at-risk population groups
in the Pacific are islander and Aboriginal communities in endemic areas. These people could be
expected to have stored ciguatoxins in their bodies
and be particularly susceptible to eating more
ciguateric fish. Because of the high risk in some
Pacific locations, 90% of fish eaten is imported and
comes out of a can (Lewis, 1986b).
The health risk of ciguatera to travellers to endemic regions is similar to that of indigenous
population groups (Lange et al., 1992; Sanner et al.,
1997). Lange et al. (1992) warned that barracuda
should never be eaten, and travellers should exercise
caution when considering other fish dishes, notably
grouper and red bass. For visitors to Australia,
narrow-barred Spanish mackerel and coral trout
could be considered potentially hazardous species.
4.3. Future exposure trends
According to Levine (1995), ciguatera is the most
common fish intoxication and is increasing in incidence, prevalence and distribution, as the world
increasingly becomes a ‘global village’. Consumption of seafood is increasing as its health benefits
become more widely known, and there is increasing
popularity of reef fish in temperate markets. Americans, for example, ate 16 lb (about 7.3 kg) seafood
per person in 1989, a 25% rise over 1980, and
consumption is expected to rise to about 20 lb (9
kg) / person by the year 2000 (Spalding, 1995).
Together with a worldwide increase in toxic dinoflagellates (IOC, 1991; Hallegraeff, 1993; Lech´ and Sierra-Beltran,
´ 1995), increased fish
uga-Deveze
consumption is likely to contribute to an increasing
incidence of ciguatera.
Glaziou and Legrand (1994) reported that cigua-
115
tera may be becoming more common in the Pacific,
is not restricted to a few species of fish, and tends to
appear in new areas. However, Lewis (1992b) reported that over the past 15 years in the Pacific area
some countries recorded a decrease in the problem
(New Caledonia, Marshall Islands), other countries
an increase (Kiribati, Tuvalu, French Polynesia),
while still other countries recorded an increase
followed by a decrease (Tokelau, American Samoa,
Western Samoa, Fiji and Vanuatu). The fact that
cases of ciguatera are being recognised with increasing frequency in the US (Juranovic and Park, 1991;
Barton et al., 1995) may in part be a result of better
reporting.
5. Risk characterisation
In this section, an attempt is made to summarise
the nature and magnitude of the risk of ciguatera,
health and economic impacts of the disease, and
uncertainties and problem areas in combating it.
5.1. Nature and magnitude of risk
5.1.1. Statistical risk of contracting ciguatera and
risk-taking behaviour
Many factors influence the statistical risk of
contracting ciguatera. For example, the fish species
and where it was caught, the size of the individual
fish and the size of the portion consumed. The
statistical risk varies with country and species of fish
(Hokama et al., 1993). The risk of contracting it on
Niuato Island in Tuvalu is 1 / 10 (Dalzell, 1994). In
Micronesia, the risk from eating moray eel viscera
may be .1 / 20. With Hawaiian jackfish (Caranx sp.)
the risk is 1 / 100 (Hokama et al., 1993).
The magnitude of the risk of ciguatera to human
health in Australia and the economic impact of the
disease has not been investigated to any extent. In
coastal Queensland, the annual risk of contracting
ciguatera is about 1 / 3000 (Gillespie et al., 1986);
and the risk of contracting it from a meal of coral
trout (Plectropomus spp.) from areas normally fished
is ,1 / 5000 (Pearn and Lewis, 1994). The objective
risk of fatality is ,1 / 1000 of clinical cases in
Australian (Tonge et al., 1967) and Polynesian
reports (Bagnis et al., 1979).
Dalzell (1992) reported that native seafood con-
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L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
sumers in areas with ciguatera generally hold a
fatalistic attitude, and occasional poisoning is accepted as inevitable. According to Glaziou and
Legrand (1994), health departments in the Pacific
region tend not to regard ciguatera as a serious issue,
and concentrate their limited resources on other
priorities, for several reasons — intoxication is
accepted as inevitable, the disease is rarely fatal, and
there is no available preventive or remedial medical
treatment. Pearn and Lewis (1994), who surveyed
scientists and physicians at a ciguatera management
workshop in Australia, also reported risk-taking
behaviour with regard to ciguatera.
5.1.2. Impact on human health and health costs
Brusle´ (1997) estimated that each year 10 000–
50 000 people suffer from ciguatera annually worldwide, with significant morbidity (gastrointestinal,
cardiovascular and other symptoms), loss of working
days, hospital stays and even, in a few cases, death.
As ciguatera is a significant public health concern, it
is serious that the risk of contracting the disease may
be increasing.
In the US, Ragelis (1984) estimated there were
more than 2000 cases of ciguatera annually, with
about 1300 in South Florida. Treating such cases is
expensive. In Puerto Rico and the US Virgin Islands,
morbidity rates range from 10 to 27 people per
thousand. Losses in work time and medical expenses
from ciguatera in Puerto Rico average $1000 per
case (Anonymous, 1999).
Todd (1995) reported that as many as 325 cases of
ciguatera are seen each year in Canada. He estimated
the cost at $1100 / case, or about $351 000. In 1997,
Todd said that, based on the assumption that there
may be as many as 300 cases in Canada each year,
either from tourists visiting tropical areas or from
tropical fish consumed in Canada, an assuming each
of these cases costs $4000, the total annual cost
could be as high as $1 236 000 (Canadian dollars),
reflecting the rising costs of medicine.
Throughout Pacific island countries there is a
heavy dependence on the inshore fishery resource of
reefs for dietary protein and animal fats. Nowhere is
the impact of the disease greater than in the atoll
countries of the Pacific, where intake of reef fish is
often more than 100 g / person per day (Lewis,
1992b). Ciguatera is also important in relative terms,
being one of the more commonly reported diseases
(Ruff and Lewis, 1994). In French Polynesia, about
one-third of the notified patients have to be confined
to bed. The incapacity to work lasts from 2 to 7 days,
but may last for 4 weeks. In the Tahitian community,
Bagnis et al. (1992) estimated that, on average each
year, ciguatera results in the loss of about 4000
working days. If a simple, fast, reliable and cheap
assay was available for the diagnosis of ciguateric
fish, most of these costs would be avoided.
5.1.3. Impact on fishing industries
Johannes (1990) suggested that the inshore
fisheries resource is of greater importance per capita
to Pacific island countries than in any other region of
the world. Many of the social and economic capabilities in the Pacific countries depend on fisheries,
as agricultural activities are limited by the nonavailability of sufficient arable land (Glaziou and
Legrand, 1994). Ciguatera imposes severe economic
strains on these economies, especially in certain
underdeveloped tropical areas (Banner, 1976). It
makes islanders more dependent on imported foods,
which decreases self-sufficiency and forces native
populations into a cash economy and away from
traditional means of subsistence. This leads to greater dependence on industrialised countries (Lewis,
1986a). In the Tahitian community, Bagnis et al.
(1992) estimated that ciguatera resulted in the loss of
about 3000 tons of reef fish that were banned from
sale in the market place each year.
Ciguatera can reduce or prevent export of reef
fish, which can be a major source of income, from
island communities (Lewis, 1992b). There have been
confirmed outbreaks of ciguatera in Hong Kong
caused by imported fish since the 1980s, and the
number of reported outbreaks is increasing (Sadovy,
1997). In March–April 1999, a large outbreak in
Hong Kong (at least 200 people affected and 100
hospitalised) was attributed to live ciguatoxic fish
imported from a small island country in the Pacific.
Hong Kong residents have become more wary about
consuming fish, which has affected exports of fish to
Hong Kong from all countries. Apart from size
restriction, which is not fail-safe, there are no means
at present of ensuring that coral trout and other reef
fish exported live will not cause ciguatera.
The marketing of seafood is greatly affected by
media attention following outbreaks. The economic
loss from fish toxicity and adverse publicity is more
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
than US$10 million annually in the Caribbean, plus
liability insurance for litigation (De Sylva, 1994).
Although Puerto Rico has quarantined sales of the
tropical reef fish species that frequently carry
ciguatoxin, these fish have sometimes been sold
illegally to consumers, causing outbreaks of poisoning (Anonymous, 1999). In Australia, outbreaks may
be documented with front-page headlines and consumption of fish can drop considerably for many
weeks after such events (Lewis, 1992b).
5.1.4. Impact on tourism
Tourism is becoming increasingly important to
tropical and subtropical island communities. In Australia, the Great Barrier Reef is perhaps the most
popular area for tourists to visit, and it is likely that
even one outbreak of ciguatera among tourists would
cause considerable media coverage and a drop in
both national and international tourist numbers. Such
economic effects on tourism have been felt in the
Caribbean (Lewis, 1986a).
5.1.5. Likelihood of litigation
In recent years, outbreaks of foodborne disease
have served to heighten awareness among consumers. Because of these events, and strong consumer
organisations in some countries, public awareness of,
and demands for, food safety have increased markedly. With this has come increased litigation.
Litigation concerning a case of ciguatera in a US
court favoured the fishing industry, although recommendations were made to implement due notification
at the point of sale (Nellis and Barnard, 1986).
According to Hahn (1991), this implies that fish
harvesters, seafood distributors and seafood restaurants should give written notice of the potential risk.
Although fair to consumers, this would have economic ramifications for communities and countries in
ciguatera-endemic regions that rely on tropical fish
export and tourist trade.
In Australia in 1988, the New South Wales
Department of Health brought charges against a
Sydney-based fish wholesaler allegedly responsible
for marketing toxic mackerel that resulted in 64
reported cases of ciguatera. In this case, the magistrate’s decision favoured the wholesaler. However,
an outcome in favour of the prosecution would set a
precedent that may damage the Queensland mackerel
117
fishery, if individual fishers become liable for toxic
fish (Capra and Cameron, 1991).
Litigation regarding a case of ciguatera in Bermuda resulted in an out-of-court settlement. The
defence case was based on an interpretation of
internationally recognised laws of tort (Maran,
1991). In a paper entitled ‘Ciguatera poisoning:
Current issues in law’, Payne (1994) reviewed the
current situation with regard to liability under
Queensland law relevant to ciguatera. The author
considered it inevitable that there will be successful
litigation in respect of the disease, and recommended
that all sectors of the fishing industry be acquainted
with their responsibilities under common law and
State statutes to prevent litigation in the event of an
incident. Payne (1994) suggested that ‘‘the industry
should be pro-active and consider what steps can be
taken to address potential liability’’.
5.2. Uncertainties and problem areas in combating
ciguatera
In 1989, WHO stated that control mechanisms for
ciguatoxin were impossible at that time, owing to the
lack of a reliable method for testing fish for toxicity,
and recommended investigations in this field. WHO
(1989) recognised the importance of monitoring
systems for ciguatoxins in fish and the need to carry
out long-term observations for detection of trends in
dinoflagellate populations and environmental parameters that affect them. This would lead to the
development of computer models for the prediction
of the occurrence of toxic blooms. WHO (1989)
recommended that medical doctors be made aware of
the signs and symptoms of diseases caused by
marine biotoxins, and the importance of reporting
cases to health authorities.
More than a decade later, considerable effort has
been made towards developing reliable testing methods, and before many more years an internationally
recommended method of analysis may allow the
setting of maximal acceptable concentrations for
ciguatoxins in fish. Less progress has been made on
the monitoring of dinoflagellate populations to predict toxic blooms, or on the gathering of clinical
information.
Complete eradication of the problems associated
with ciguatera in Australia is unlikely unless consumption of reef fish (and fish from Platypus Bay) is
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L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
stopped. Given that this is unlikely and undesirable,
what are the options for limiting the effects of this
form of fish poisoning? Clearly some form of control
on catching, traceback and consumption of ciguateric
fish is required. This needs to be backed with
research on the factors associated with increased
toxin production by G. toxicus; on a quick, cheap
and simple detection method for ciguateric fish and
ciguatoxins in clinical samples; and on a better,
preferably oral, treatment of the intoxication.
5.2.1. Variable production of toxin by
dinoflagellates
Ecological studies on G. toxicus are needed to
determine what factor (or factors) stimulates its
proliferation and, more importantly, its production of
ciguatoxins. Because many wild populations of G.
toxicus do not produce toxins, simply monitoring
abundance of algae is unsatisfactory for predicting
outbreaks.
G. toxicus populations are not monitored for
regulatory purposes in Australia or elsewhere. If
routine monitoring of dinoflagellates was to be done,
toxicity monitoring of each population would need to
be an integral feature. Monitoring the toxicity of fish
at various levels of the food chain at various sentinel
sites may also be of benefit in predicting outbreaks.
This may enable timely action, such as closing an
area to fishing, or restricting types or sizes of fish
caught, before an outbreak occurs (Ruff and Lewis,
1994).
5.2.2. Prevalence and identification of toxic fish
Imposing size restrictions for consumption of
high-risk species would be practical and feasible, but
not infallible, in preventing ciguatera, as biological
systems are never exact and smaller fish have been
known to cause the disease. In addition, this concept
requires further research to arrive at the most suitable
weights for restriction for each species. Some species
from some areas can never be consumed without
considerable risk.
A cheap and reliable test for ciguatoxins, including one that can be applied to fish on an individual
basis as well as to human clinical samples, is
required urgently. As new rapid detection methods
become available, resources need to be provided for
large-scale testing with these methods, in conjunction with verification using bioassay and chemical
methods. This testing could be done in collaboration
with fish exporters, and thereby assist them in
identifying toxic fish.
After validation, such methods could be used
routinely for identifying toxic fish, at least on a
reef-by-reef basis. However, this concept is fraught
with administrative and policy problems. For example, who should do the monitoring? Who should
pay? Who has legal liability? How many or what fish
should be tested? What concentration of ciguatoxin(s) should be considered toxic, bearing in mind that
the toxin is cumulative? An acceptable cost for
ciguatera screening has not been determined. According to Lewis (1994b), this will relate to the
added value screened fish will attract in the marketplace, and an add-on cost of ,10% may be reasonable.
Implementation of a useful screen would result in
improved marketability of fish caught in ciguateraendemic areas, and removal of toxic fish before
consumption would lead to improved community
health standards. Fisheries could be opened to
species that are currently restricted because of frequent toxicity. Once an effective screen was available, new and potentially lucrative fisheries could be
established. For example, red bass, and perhaps
chinaman fish and paddletail, fisheries could be
established in Queensland once the risk of ciguatera
was removed (Lewis, 1994b).
The concentration of ciguatoxin considered potentially harmful would need careful consideration from
the point of view of accumulation of toxin and repeat
attacks. There is currently no regulatory limit for
ciguatoxin in fish in the Australian Food Standards
Code. Another problem at the moment is that
currently used tests have difficulty in detecting
ciguatoxin at concentrations much below the lowest
toxic level (0.1 mg / kg), which means that detecting
a concentration that allows for built-in risk factors
may be beyond the scope of the assay. However, the
true impact of build-up of ciguatoxins from consumption of low-toxicity fish is still unclear.
5.2.3. Fish traceback
If a fish causing a confirmed case of ciguatera
could be traced back to its reef of origin, it may be
feasible to control fishing for high-risk species in that
localised area for a certain time. While tracing a
suspect fish back to its home waters is sometimes
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
achieved, it is often complex or impossible. In
Australia, tracing fish caught by recreational anglers
is relatively simple, but tracing fish from commercial
outlets is more complex, because of a lack of a
ticketing system, especially in the middle
(wholesaler) stages of distribution (Rawlin and Herfort, 1999).
5.2.4. Gathering and use of clinical and
epidemiological data
It is necessary to learn more about the epidemiology of ciguatera by gathering information. At present
the disease is under-reported and sometimes misdiagnosed. It would help to have a more specific
clinical definition of the disease, and defined criteria
for differential diagnosis. Studies are also required
on pathophysiological mechanisms underlying the
disease, its potentiation by alcohol, and the scientific
basis of the allergy-like syndrome that persists in
some patients. Immunological studies on ciguatoxins
in laboratory animals and eventually humans could
be considered, with a view to producing a vaccine.
Australia does not contribute to the South Pacific
Commission database. However, there is an Australian database with records starting in 1965, which
was established by the Queensland Department of
Primary Industries. The database currently contains
details of about 400 outbreaks and about 1000
individual cases of ciguatera. It is estimated that only
10–20% of the cases in Australia are reported, and
similar under-reporting is expected in other areas.
Accurate epidemiological and clinical data need to
be collected and compared, and utilised for risk
management. Fish factors, including fish species,
size and origin should also be included wherever
possible. Such information will be available only if
case histories are faithfully reported following outbreaks and case history information is properly
followed up. There is also some value in the
argument of Williams (1998) that, like other foodborne illnesses of public health significance in
Australia, ciguatera should be made a notifiable
disease.
Oral treatments are generally considered more
desirable and cheaper than intravenous infusions.
Along with research on the pathophysiology of
ciguatera, new treatment possibilities could be explored. As intravenous mannitol is currently the
preferred treatment, more should be learned about its
119
pharmacology and mechanism of action in relation to
ciguatera. Ideally, there should be a randomised,
controlled, double-blind trial of mannitol therapy to
establish its true efficacy, particularly in relation to
time of its administration in the course of the
disease.
5.2.5. Prevention of ciguatera at the individual
level
Education of people about the dangers of ciguatera
and what they can do about it remains a problem
area, particularly in the light of common risk-taking
behaviour (Pearn and Lewis, 1994). Ruff and Lewis
(1994) listed various ways individuals can reduce
their risk of contracting the disease, such as by:
• avoidance of warm water reef fish, particularly
those with a known propensity to be toxic, and
avoidance of certain pelagic fish that feed on
them (e.g., barracuda and mackerel), especially in
areas with a history of ciguatera;
• avoidance of all fish at locations that are known
sources of toxic fish;
• complete avoidance of moray eels, except when
captured in areas with no history of ciguatera;
• avoidance of larger carnivorous fish (e.g .2.5
kg);
• avoidance of head, roe and viscera of potentially
toxic fish; and
• consumption of only a small portion (,50 g) of
any one fish at the first sitting.
Acknowledgements
This review was updated and revised from a larger
review written for the National Office of Animal and
Plant Health, Agriculture, Fisheries and Forestry —
Australia, Canberra: Ciguatera fish poisoning: a
review in a risk-assessment framework, L. Lehane,
1999. The authors are grateful to a number of
personnel from the following organisations for their
assistance: Agriculture, Fisheries and Forestry —
Australia, Aquacairns, Australia and New Zealand
Food Authority, New South Wales Department of
Health, Queensland Department of Primary Industries / National Seafood Centre (Brisbane) and
Queensland University of Technology.
120
L. Lehane, R. J. Lewis / International Journal of Food Microbiology 61 (2000) 91 – 125
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