Rev. sci. tech. Off. int. Epiz., 1997,16 (2), 661-672
Seafood-associated diseases
and control in Canada
E.C.D. Todd
Health Protection Branch, Health Canada, Sir Frederick G. Banting Research Centre, Postal Location: 2204 A2,
Ottawa, Ontario K1A 0L2, Canada
Summary
Paralytic shellfish poisoning (PSP) has been documented for two centuries and
control programmes have been operated for fifty years. Although some illnesses
are reported almost every year, the last known death from PSP occurred in 1981.
In more recent years, amnesic shellfish poisoning, ciguatera poisoning,
diarrhoetic shellfish poisoning, scombroid (histamine) poisoning and tetramine
poisoning have been documented. The most frequently observed of these
diseases is scombroid poisoning from improperly stored fish, but PSP and
ciguatera poisoning have the most serious consequences. Vibrio infections
arising from naturally-contaminated shellfish are virtually unknown, and viral
illnesses from polluted harvested waters are rare. Control is achieved through
monitoring of waters for indicators of human pathogens. Inspection systems
based on the hazard analysis and critical control point principles are being
introduced into all areas of fish and shellfish harvesting. The Inspection
Directorate of the Department of Fisheries and Oceans joined the new Canadian
Food Inspection Agency in 1997, which co-ordinates all Federal control measures
for food in Canada.
Keywords
Canada - Control - Microbiology - Public health - Seafood - Toxins.
Introduction
In Canada, illness associated with the ingestion of seafood
(fish and shellfish) accounts for approximately 7% of all
incidents and 4 % of all reported foodborne illness cases,
based on 1 9 7 5 to 1 9 8 4 data ( 2 0 ) : a slight increase was
recorded in 1 9 9 0 and 1 9 9 1 , with 8 % - 9 % of incidents and
4%-8% of cases, respectively ( 2 9 ) . These figures compare
with data reported in the United States of America (USA),
where illness was recorded in 6%-9% of all foodborne disease
outbreaks and l % - 4 % of cases from 1 9 8 8 to 1 9 9 2 ,
respectively (4). In Canada, in incidents where the aetiology
was known, micro-organisms were responsible for 7 2 % ,
chemical agents 2 1 % and seafood toxins 2 % of incidents
which occurred between 1 9 7 5 and 1 9 8 4 (20). More recently,
this percentage has changed slightly: seafood toxins were
responsible for 4 % of incidents
compared
with
micro-organisms ( 6 7 % ) and chemical agents ( 2 0 % ) from
1990 to 1 9 9 1 ( 2 9 ) . However, many incidents involving
marine foods were of unknown aetiology. The most severe
acute disease, paralytic shellfish poisoning, has been known
since historic times, but other seafood toxins have only been
identified as causes of human morbidity in recent years.
Paralytic shellfish poisoning
In Canada, paralytic shellfish poisoning (PSP) has been
documented since 1793 in British Columbia, and since the
1880s in the St Lawrence Estuary, Quebec, and the Bay of
Fundy between New Brunswick and Nova Scotia. In 1 9 8 2 ,
PSP was reported from Newfoundland for the first time ( 1 1 ) .
The concentration of toxins in shellfish varies geographically,
seasonally and between species. The highest levels of PSP
toxins are recorded between June and September in the
St Lawrence Estuary and the Bay of Fundy, and between April
and November on the British Columbia coast. The Alaskan
butter clam (Saxidomus giganteus, Deshayes 1 8 3 9 ) on the
662
Rev. sci. tech. Off. int. Epiz., 16 (2)
west coast can remain toxic throughout the year. Despite the
fact that health officials and the public have been aware of PSP
for many years, there is no indication that the numbers of
incidents per decade have decreased over time (Table I).
Fewer illnesses may be occurring in the 1990s: illnesses and
deaths seem to have been more frequent from the 1950s to
the 1960s, but this may be an artefact of reporting frequency
compared with previous years. Overall, 1 0 6 incidents, 5 3 4
cases and 3 2 deaths have been documented since 1880, with
most cases and deaths associated with the St Lawrence
Estuary (22). The largest concentration of illnesses in Canada
occurred in 1 9 7 4 , with 4 3 cases between 3 0 April and 18
August in this region demonstrating toxin levels of up to
4,900 pg/100 g (median, 1,750 pg/100 g) (10). Most recent
cases have involved recreational harvesters or their families,
often as a result of ignoring notices regarding areas which had
been closed to harvesting. Occasionally, toxic molluscs are
sold to food service outlets and patrons become ill. However,
there are fewer deaths today because of better medical care,
even though the toxin levels can be as high as in the past
(26). The last recorded death from PSP occurred in 1 9 8 1 .
Mussels (Mytilis edulis), clams (Árctica islandica,
Mya
arenaria, Mercenaria mercenaria, Mesodesma arctatum and
Protothaca staminea), whelks (Buccinum, Colus and Thais
spp.) and west coast oysters (Crassostrea gigas) are the
molluscs most frequently associated with PSP. Atlantic
scallops (Placopecten magellanicus) can become extremely
toxic but only the adductor muscles of these are permitted to
be marketed.
illness report also came from the north shore of the
St Lawrence Estuary: in this case, PSP toxins were found in
the hepatopancreases of the lobster which had been
consumed. In subsequent surveys on the east coast, a few
lobsters were found to contain > 2 5 0 pg PSP toxins/100 g
cooked hepatopancreas, up to a maximum of 7 2 2 pg/100 g
(28). No toxin, however, was found in the meat. The highest
levels of PSP toxin were recorded in lobsters caught in the
Gaspé area. As cooking does not destroy the PSP toxins and
the hepatopancreases are eaten as tomalley (lobster liver), the
Health Protection Branch of Health Canada advises that the
public eat no more than two hepatopancreases at any one
meal (28).
Lobsters trapped in canyons off the Georges Bank have also
been found to contain PSP. The origin of the PSP in lobster
hepatopancreases is not known, but is assumed to be related
to the food supply. In shallow water (as in the Gaspé area), the
source is presumably shellfish containing PSP toxins, but
deep-water food sources are less well known and
photosynthetic Alexandrium
(an algal
dinoflagellate
producing PSP toxins) does not travel far below the surface.
One possible source of toxins may be dead or dying cells
which fall to the ocean floor and are incorporated into the
food chain. However, there is no clear indication as to
whether the Alexandrium come from inshore blooms being
transported to the Georges Bank or from undetected local
blooms (31).
The carnivorous northern moonshell (Lunatia heros), a
potential new seafood product from the southern part of the
Gulf of St Lawrence, has been shown to contain PSP toxins
since 1 9 8 9 ( 3 2 ) . The source of toxicity is not known, but
A. excavatum is present in significant numbers under the ice
New problems involving PSP toxins have developed during
the last decade. In 1990, unconfirmed reports were made of
illnesses associated with the consumption of lobsters
(Homarus americanus) in the Gaspé area of Quebec. One
Table I
Incidence and cases of paralytic shellfish poisonings reported in Canada, by region, between 1880 and 1995
Decade
1880-1889
1890-1899
1900-1909
1910-1919
1920-1929
1930-1939
1940-1949
1950-1959
1960-1969
1970-1979
1980-1989
1990-1995
Total
St Lawrence
Estuary
1
C
D
2
0
2
2
3
2
3
2
12
8
11
4
51
2
0
12
2
5
!3
10
12
47
60
44
4
211
2
0
5
0
2
0
4
2
5
3
2
0
25
Bay of Fundy
1
6
2
3
2
9
4
6
32
C
47
27
34
6
42
4
10
170
British Columbia
D
2
0
0
0
0
0
0
2
I
1
1
2
3
15
0
22
C
7
61
12
25
48
0
153
Newfoundland
D
3
0
1
0
1
0
5
I: incidents
C: cases
D: deaths
Source: E.C.D. Todd (22), updated from Department of Fisheries and Oceans data and Annual Summaries of Foodborne Disease
1
1
0
1
C
4
0
4
Total
D
1
C
D
0
0
0
2
0
2
2
3
8
6
6
16
20
31
10
106
2
0
12
2
5
60
44
107
65
127
100
14
538
2
0
5
0
2
2
7
2
6
3
3
0
32
663
Rev. sci. tech. Off. int. Epiz., 16 (2)
(< -1°C) and this could explain why shellfish may be toxic in
early spring. Moonshells have also been found to be toxic,
along with Buccinum undatum, a carnivorous whelk, on the
Georges Bank (31).
Amnesic shellfish poisoning
In Japan and western Europe, thousands of human cases of
dirrhoetic shellfish poisoning (DSP) have been linked to
phytoplankton species, including Dinophysis acuminata and
D.fortii. These dinoflagellates produce okadaic acid which
causes diarrhoea in humans. In 1 9 8 9 , dinophysis toxin 1
(DTX-1), an analogue of okadaic acid, was isolated from
Prince Edward Island mussels at a level of 0 . 1 5 µ g / 1 0 0 g
digestive gland (12), and in the summer of 1 9 9 0 , 1 3 people in
eastern Nova Scotia who consumed locally cultured mussels
developed DSP between one and eight hours later (17). The
principal symptoms were nausea, abdominal cramps,
dianhoea and weakness. Recovery time for the victims ranged
from one to four days. Dinophysis norvegica was found in the
digestive glands of the mussels, but the dinoflagellate
Prorocentrum lima may have been the toxin source. Based on
an assumption that 100 µg DTX-1 was present in 1 0 0 g of
mussel soft tissue, the victims ingested between 1.4 and
6.0 µg DTX-l/kg body weight ( 2 8 ) . In 1 9 9 3 , low levels of
DTX-1 were found in mussels at the same harvest site and at
other locations in Nova Scotia (9). Mussels from two locations
in Bona Vista Bay, Newfoundland, caused a number of
poisonings in October 1 9 9 3 . Analysis showed that sampled
mussels contained up to 4 µg DTX-1/100 g digestive gland
(8). Significant levels of D. norvegica were present in the
harvest areas at a water temperature of 6°C. Complaints of
DSP-like illnesses occur almost every year in eastern Canada,
but the cause is not known (see 'Undetermined seafood toxin
illnesses', below).
Only one confirmed outbreak of amnesic shellfish poisoning
(ASP) has been reported world-wide. This occurred in Canada
in November and December 1 9 8 7 , due to consumption of
cultured mussels harvested in Prince Edward Island. One
hundred and seven cases (mostly from Quebec, Ontario and
the Maritime provinces) were recorded, but many more
unreported cases were suspected ( 1 6 ) . Mild gastroenteritis
was experienced by many of the victims, but the most
distinctive feature of the outbreak was the disorientation and
memory loss observed in the most seriously affected cases.
Three victims died, and a few of the hospitalised cases
continued to have short-term memory loss. Domoic acid, a
glutamate-like excitotoxic amino acid which depolarises
specific brain cells, was identified as the toxic agent. Up to
1,280 µg/g soft tissue were found in the mussels and, where
information was known, doses ranged from 15-20 mg per
person (for those unaffected) to 2 9 5 mg per person (for those
with severe neurological symptoms). The most serious cases
received doses of 1.9-4.2 mg domoic acid/kg body weight
(23).
The domoic acid originated from a diatom
Pseudonitzschia multiseries, which was blooming in the area
where the mussels were harvested. Since 1 9 8 8 , a
comprehensive shellfish monitoring programme has been
implemented on Canadian coasts by the DFO, with the action
level set at 2 0 µg domoic acid/g soft tissue. Even though in
most years since 1 9 8 7 the domoic acid action levels have
occasionally been exceeded, no further illnesses have been
recorded in Canada. The reason why the Canadian outbreak
occurred has been examined, but no explanation has been
found. The bloom of P. multiseries in the autumn/winter of
1987 was extensive on the eastern Prince Edward Island
coast, and growth only diminished when snow cover on the
surface ice was too deep to allow adequate photosynthesis.
Domoic acid production depends not only on the availability
of nitrate, but also on the cessation of cell division and the
presence of light. Cells in the stationary phase remain viable
for weeks and continue to release domoic acid into the water.
Cells will even continue to produce domoic acid at sea
temperatures of 0°C (19). An estimated 1,000 kg of domoic
acid were produced in the eastern Prince Edward Island
estuaries between 1987 and 1 9 8 8 (16). Blooms have occurred
since that period, but in subsequent years were less extensive,
when domoic acid concentrations in the autumn were
sufficient to close harvesting for a short period only. In
October 1991, a limited bloom was recorded from northern
Prince Edward Island for the first time.
Sporadic episodes of DSP and DSP-like illnesses are now
expected on Canadian coasts. With rapid follow-up of
consumer complaints, identification of the toxic components
and the origin (whether Dinophysis spp. or other sources) may
be possible. The number of people at risk has increased with
the expansion of the cultured mussel industry in the
Maritimes during the last two decades.
Toxin-producing blooms have been documented from the
Maine and Texas coasts. In addition, low levels of domoic acid
produced by P. pseudodelicatissima
were found in the Bay of
Fundy. In September 1 9 9 1 , P. australis caused deaths of
pelicans and cormorants which consumed anchovies off
Monterey Bay, California ( 2 3 ) . Domoic acid has also been
recovered from shellfish and crabs harvested on the west coast
Most illnesses arise from recreational harvesters who collect
shellfish in areas which are officially closed. Education is the
method used to prevent these incidents. However, in remote
shoreline areas or in deep-water locations which have not
been monitored, the potential for toxic shellfish remains.
When new ventures are attempted for seafood products in
these areas, the Department of Fisheries and Oceans (DFO)
conducts tests before any harvesting begins.
Diarrhoetic shellfish
poisoning
664
of the USA, and may have caused illnesses in 2 4 Washington
State residents, although this was never confirmed ( 2 3 ) .
Therefore, ASP may potentially occur at a number of North
American locations. None of the occurrences listed above
would have been recognised without the investigation of the
1987 Prince Edward Island outbreak, thus local awareness is
important to determine potential hazards. Low levels of
domoic acid are probably not uncommon in the marine
environment, and sources are perhaps varied, but levels
sufficient to cause human illness are reached only under
unusual circumstances. The increased demand for seafood
products generated by aquaculture will increase this risk.
fíev. sci. tech. Off. int. Epiz., 16 (2)
Boiling whelks for 1 h will not destroy tetramine, but removal
of the salivary glands is supposed to render the whelks edible.
However, tetramine has been found at lower levels in other
tissues. Illnesses have been reported from Japan and Scotland,
as well as from Canada ( 2 2 ) . The origin of the tetramine is
suspected to be a metabolic product used in obtaining prey or
in defence against predators. As production of tetramine
appears to be restricted to certain species and locations, local
knowledge is important to avoid consumption of toxic
shellfish or to ensure that the most toxic parts, e.g., the
salivary glands, are removed from a suspect product.
Ciguatera poisoning
Tetramine poisoning
In southwestern Nova Scotia, several episodes of tetramine
poisoning have been described in the past, but only in 1991
were whelks first examined for tetramine (30). An average of
1.3 mg tettamine/g of whelk soft tissue caused blurred vision,
light-headedness, staggering, flushing and weakness in four
people 3 0 min after they had consumed whelks. The doses
ingested ranged from 5 0 to 2 3 0 mg/kg body weight (22). The
Neptunea decemcostata
whelks which caused the illnesses
were relatively large and had been collected during scallop
trawling. In 1 9 9 4 , another case of tetramine poisoning
confirmed by mouse bioassay occurred in the same region.
The area had been closed because PSP toxins exceeded the
limits for safe harvesting. In 1 9 9 5 , cooked Neptunea
whelks were consumed by an individual who then developed
typical tetramine poisoning symtoms, but confirmation
was not possible. The ingestion of certain species of whelk
(genera Neptunea, Buccinum, Fusitriton) is now known to
have the potential to result in severe headaches, dizziness and
abdominal cramps as a result of the presence of tetramine
(tetramethylammonium ion) in the salivary glands and to a lesser extent in other organs - of the whelks.
Neptunea decemcostata is widespread in the southern region
of Atlantic Canada, but is only known to contain tetramine in
the Bay of Fundy. Presumably some environmental factors are
important for production of this toxin by the salivary gland,
but these are not known. Since tetramine poisoning is
typically mild, a few incidents will probably continue to occur
in areas of the Bay of Fundy where whelks are eaten.
Another tetramine incident was reported in Labrador in 1994.
A family became severely ill after eating cooked Neptunea
despecta tomata whelks obtained as a by-catch from scallop
dragging. Results of capillary zone electrophoresis-mass
spectrometry analysis revealed that the Neptunea contained
430 µg tetramine/g of cooked tissue ( 3 3 ) . Choline and a
choline derivative were also present and may have
contributed to the illness. A similar tetramine concentration
was found in N. decemcostata
whelks from Nova Scotia
(460µg/g).
Canadians have been affected by ciguatera through the
consumption of tropical fish, mainly when travelling in the
north Caribbean region or occasionally through fish imported
into Canada ( 2 1 ) . Intoxications caused by the consumption
abroad of tropical fish are probably frequently misdiagnosed
by Canadian physicians who may lack knowledge of
ciguatera. Most of the reported cases have been diagnosed in
tropical disease centres in large metropolitan hospitals,
especially when no fish samples are available for analysis. The
largest outbreak of ciguatera occurred in 1987, when 5 7 of 61
Canadians who ate a fish casserole in Cuba developed
symptoms on the flight home or shortly after landing (7).
The second group of individuals who are exposed to
Ciguatoxins are those who buy tropical fish from local fish
markets or who eat such fish in restaurants. The first of these
incidents to be confirmed by mouse bioassay occurred in
1983, and others are documented on average about once
every 10 months (Table II). Whereas a variety of fishes was
implicated in the 1980s, barracuda (Sphyraena spp.) has been
the main species implicated in ciguatera poisonings since
1993. Imports of barracuda appear to be increasing, despite
the fact that this fish is one of those most likely to contain
Ciguatoxin: the sale of barracuda is banned in the Dominican
Republic (1). These incidents often involve immigrants who
originate from countries where tropical fish are eaten. The
largest of these outbreaks occurred in 1984 and involved nine
individuals of oriental origin who ingested different parts of a
grouper fish. In the six months between August 1 9 9 6 and
February 1997, six episodes were documented, which created
increased concern in regard to this particular intoxication.
Most of the fish implicated are now believed to have come
from an area known by fisherman to be toxic. One factor
which explains why ciguatera poisoning has only been
recognised recently is the increased immigrant populations
from tropical countries and the greater number of Canadian
tourists who visit such countries. Many immigrants are now
demanding tropical fish of differing varieties, and the volume
of such imported fish has doubled over the last few years.
Immigrants from Sri Lanka, for example, are fond of
barracuda and will try to find an importer to obtain this fish.
665
Rev. sci. tech. Off. int. Epiz.. 16 (2)
Table II
Reports of ciguatera poisonings in Canada from 1983 to 1997 (22)
Date
Food
Location
Place of acquisition
January 1983
Dried barracuda
No. ill (at risk) Confirmation
Toronto, Ontario
Home (brought from Jamaica]
2(2)
April 1984
Grouper
November 1986 Grouper
Ontario
Ontario
Retail
Restaurant
9(9)
1(3)
April 1987
Ontario
Quebec
Retail
7(7)
1(2)
2(2)
4(4)
October 1989
June 1989
Mongol snapper
Mahi-mahi
Retail
Retail
Grouper
Ontario
Grouper (Fiji red salmon) Vancouver, British Columbia Retail
February 1990
September 1993 Barracuda
Toronto, Ontario
Restaurant
April 1994
August 1996
Barracuda
Barracuda
November 1996 Barracuda
January 1997
Doctor fish
February 1997
February 1997
February 1997
Exporting country
Mouse +ve
Mouse +ve
Jamaica
USA
Diagnosed
No
?
Mouse +ve
?
Mouse +ve
Mouse +ve
Spain
?
Fiji Islands
1 (?)
4(4)
Diagnosed, no fish left USA
Mouse +ve
USA
Toronto, Ontario
Toronto, Ontario
Retail
Fish market
2(2)
Mouse +ve
Montreal, Quebec
Restaurant in club
5(?)
Retail
Retail
1(7)
4(4)
5(5)
Diagnosed, no fish left USA
Diagnosed, mouse+ve USA
Diagnosed, mouse +ve West Indies
Diagnosed, mouse +ve Trinidad & Tobago
Toronto, Ontario
Spanish mackerel
Toronto, Ontario
Bacine fish (barracuda?) Toronto, Ontario
Barracuda and seapat
Toronto, Ontario
Retail
Retail
5(5)
?
la|
Diagnosed, mouse +ve Trinidad & Tobago
lal
|a|
a| Fish believed to come from the same area known to be toxic near the Florida Keys
Source. E.C.D. Todd (22), updated from Department of Fisheries and Oceans data and Annual Summaries of Foodborne Disease
Unfortunately, the location of the origin of these fish, as
opposed to the shipper, is usually not known, and the name
of the fish may be too local to identify the precise species, e.g.,
seapat, bacine, Fiji red salmon. Consequently, control
programmes are difficult to establish for the importing
country. At present, ciguatera poisoning is probably
considerably under-reported. Once newer methodology
replaces the mouse bioassay, more incidents may be
confirmed. However, as left-over fish is not always available
for testing, restaurants which serve tropical fish could be
encouraged to keep any remaining product whenever illness
complaints are received.
Histamine (scombroid) poisoning
Histamine poisoning was first confirmed by a laboratory in
Canada in 1975, although incidents probably occurred before
this time. Most incidents were traced to scombroid fish, such
as tuna (Thunnus spp.) and mackerel (Scomber spp.). Unlike
the 1970s and 1980s when canned tuna was the most likely
vehicle of contamination, between 1990 and 1 9 9 5 fresh tuna,
mahi-mahi or dolphin (Coryphaena
hippurus) and marlin
(Makaira spp.) were more likely to be implicated ( 2 5 )
(Table III). More incidents have occurred in the last seven
years (an average of four annually, compared with an annual
rate of 0.6 between 1 9 7 6 and 1988). The three largest
outbreaks were caused by the ingestion of smoked mackerel
(October 1 9 8 7 : 14 cases), fresh marlin (July 1991: 12 cases)
and fresh tuna (August 1994: 12 cases). This increase in tuna
steak-associated scombroid poisoning has also been
documented in the United Kingdom (2). Histamine levels of
between 2 8 mg and 7 1 0 mg/100 g.were implicated in seven
separate incidents involving tuna imported from Sri Lanka. As
most of the fish implicated in scombroid poisoning has been
imported, agreements with reputable suppliers may be the
most effective way of obtaining low levels of histamine in
scombroid and other types of fish.
Undetermined seafood toxin
illnesses
Other amines have been associated with scombroid-like
symptoms. In one episode which occurred in 1 9 9 1 , the
decomposition products putrescine and cadaverine were
found in left-over swordfish (Xiphias gladius) at levels
indicative of bacterial spoilage (70 µg and 5 9 1 µg/100 g meat
of putrescine and cadaverine, respectively). These amines are
possible contributors to scombroid poisoning and could have
contributed to the illness, even though negligible amounts of
histamine were found in the fish ( 2 7 ) . A human protein
phosphatase inhibition test showed that 112 µg okadaic acid
equivalents were present. From the description of the
outbreak, the swordfish was clearly the implicated food, but
the specific agent could not be determined. In 1991 and
1992, high (but unspecified) levels of these amines were
found in cans of salmon and caused cramps, diarrhoea and
muscle pain in two consumers during the first episode and
unspecified symptoms in one person during the second.
Shark and skate are known to decompose quickly and
sometimes release amines and ammonia, with subsequent
gastroenteritis and even burning of the mouth and throat.
From these episodes, it would appear that amines (apart from
666
Rev. sci. tech. Off. int. Epiz., 16 (2
Table III
Reports of actual and suspected histamine poisoning from ingestion of seafood in Canada from 1975 to 1995
_ „
Date
_
... .
Typeoff.sh
Histamine concentration
(mg/IOOg)
December 1975
Canned tuna
124
April 1978
October 1979
Mahi-mahi
October 1980
March 1981
February 1982
Smoked mackerel
Canned tuna
September 1983
October 1987
August 1988
February/April 1989
March 1989
August 1989
November 1989
May 1990
August 1990
July 1991
August 1991
September 1991
September 1991
November 1991
January 1992
August 1992
August 1992
September 1992
December 1992
March 1993
April 1993
October 1993
December 1993
February 1994
March 1994
May 1994
July 1994
July 1994
August 1994
February 1995
August 1995
August 1995
December 1995
Canned tuna
Smoked mackerel
Canned tuna
Smoked mackerel
Bluefish
Canned tuna
Mahi-mahi
Canned tuna
Canned anchovies
Marlin
Canned tuna
Fresh marlin
Shrimp
Anchovies (on a pizza)
Spiced mackerel
Marlin
Marlin
Fresh tuna
Fresh yellowfin tuna
Fresh tuna
Mahi-mahi
Mahi-mahi
Mahi-mahi
Canned tuna
Marlin
Mahi-mahi
Prawns
Marinated tuna
„
.
P r 0 V i n C e
p . »
Country of ong.n
Ontario
Cuba
243-339
262
132
British Columbia
Ecuador
Nova Scotia
Nova Scotia
?
305
British Columbia
Canada
Malaysia
Nova Scotia
Ontario
Canada
USA
170
1.7"»
152-158
Nova Scotia
Canada
204
26""
British Columbia
Quebec
?
Thailand
241
Ontario
7
Quebec
Quebec
Alberta
Philippines
18.1
164
lb)
7
0.4 Ibi
281-405
Test not performed
Test not performed
13-260
602
120
51
Low "
1
1
|b)
100
Test not performed
Test not performed
<10
2
| b |
British Columbia
Ontario
Ontario
British Columbia
Ontario
Spain
7
Philippines
Ecuador
{
M
)
1 (D
5 (5)
1 (1)
2 (2)
1 ID
2 (2)
1 (1)
14 (14)
1 (1)
2 (?)
3 (3)
1 (?)
3 (?)
3 (?)
2 (2)
12 (?)
Indonesia
Spain
1 (?)
4 (?)
Canada
1 (?)
?
1 (?)
1 (?)
Ontario
Ontario
7
Ontario
Ontario
British Columbia
Ontario
Ecuador
USA
USA
USA
Taipei China
7
Thailand
Test not performed
Test not performed
British Columbia
Ontario
Ontario
Test not performed
360-375
British Columbia
Ontario
Thailand
Sri Lanka
USA •
205
660-730
378-686
Ontario
Ontario
Ontario
Mahi-mahi
Fresh tuna
Fresh tuna
10-75
293-302
Ontario
Ontario
Ontario
Ontario
211-226
275-340
Number ill
Ontario
Ontario
Barbecued tuna
Fresh tuna
Fresh tuna
Smoked mackerel
|a|
1 (?)
1 (?)
1 (?)
1 (?)
w
1 (?)
2 (?)
2 (2)
w
lcl
7
1 (?)
7
1 (?)
2 (3)
lcl
w
4 (?)
3 (5)
USA
USA
7 (?)
12 (12)
USA
1 (1)
Canada
USA
4 (4)
2 (4)
7
1 (?)
,c|
a) Data incomplete from 1991 to 1995
b) Not necessarily from the can purchased by the consumer, but from the same lot of fish
c) Diagnosed as scombroid poisoning
Source: E.C.D Todd (22), updated from Department of Fisheries and Oceans data and Annual Summaries of Foodborne Disease
histamine) or other spoilage compounds may be responsible
for fish poisonings.
Illnesses have also been documented
from
other
undetermined seafood toxins. These have been reported from
Nova Scotia and Newfoundland, normally with one or two
affected individuals. Symptoms include mild gastroenteritis
and sometimes a burning or peppery sensation in the mouth.
Some of these illnesses may be the result of DSP or DSP-like
toxins, but DTX-1 levels high enough to cause symptoms
have not been found in mussels in Nova Scotia or New
Brunswick subsequent to the 1 9 9 0 outbreak (9). Attempts to
characterise these non-DSP type toxins have not been
successful to date.
667
Rev. sci. tech. Off. int. Epiz., 16 (2)
Illnesses of microbial and
parasitic origin
Between 1 9 7 3 and 1 9 9 5 (although data are incomplete for
1991 to 1 9 9 5 ) , incidents of illness were attributed to
microbes, as follows:
-
Staphylococcus aureus (37 incidents)
Salmonella (23 incidents)
Bacillus cereus ( 1 8 incidents)
Clostridium botulinum (13 incidents)
Clostridium perfringens (6 incidents)
Campylobacter jejuni (3 incidents)
Vibrio parahaemolyticus
(2 incidents)
Norwalk-like viruses (2 incidents) (20, 2 9 ) .
In both commercially canned or home-canned finfish (mainly
salmon), S. aureus was detected in 13 incidents, and the
organism, or the toxin of the organism, was demonstrated in
crab in 6 incidents. Salmonella has caused outbreaks in a
variety of marine products; examples are tuna, salmon,
kippers, lobster and crab. In one outbreak which affected 11
individuals in 1 9 9 0 , imported lappas (limpets) were
contaminated with S. Typhi. One year earlier, the same
product had been responsible for 2 1 cases of Campylobacter
infection.
Most incidents of B. cereus were associated exclusively with
molluscan and non-molluscan crustacea, e.g., shrimp, lobster
chowder, various crab products, clams and scallops.
Incidents of C. botulinum type E were associated exclusively
with home-fermented salmon eggs and home-smoked salmon
(mainly west coast salmon), trout (Salmo spp.), char
(Safvelinus alpinus) or pike (Esox lucius), but few such
incidents have occurred since 1 9 8 7 . One outbreak in 1 9 9 5
arising from home-smoked pike resulted in three cases, one of
whom died. In 1996, one person suffered from botulism after
consuming home-fermented fish heads.
Although V. parahaemolyticus
and V. vulnificus have been
found in Canadian waters and have caused wound infections,
only two single-case episodes of foodborne illness due to
V. parahaemolyticus
have been documented until recently;
these originated in contaminated oysters on the west coast.
However, in the summer of 1 9 9 7 , many cases of
V. parahaemolyticus
on the Pacific west coast of the USA and
Canada were associated with the consumption of oysters and
sales of the product were suspended temporarily. Over 5 0
cases were reported in British Colombia alone.
outbreak occurred in 1 9 9 4 , but in this case tuna salad was
only one of several foods implicated.
There have been few reports of parasitic disease. In 1989, one
case of anisakiasis was reported in Edmonton, Alberta, after a
man ate sushi prepared from an unknown fish species ( 1 4 ) .
He suffered epigastric pain and a mild fever before the worm
was removed surgically. The only previous known parasitic
infection from saltwater fish occurred in Nova Scotia in 1 9 7 2 ,
when Pseudoterranova
decipiens was recovered from the
throat of a young woman who had experienced a tingling
sensation in her throat. The parasite originated from a freshly
caught cod which had been cooked on a camp stove (13).
A new parasitic disease associated with fish occurred in May
1993, when 2 7 Canadians of Korean origin ate sashimi
prepared from uncooked white suckers
(Catostomus
commersoni) taken from an eastern Quebec river ( 1 5 ) . They
were infected by Metorchis conjunctus metacercariae which
were present in the fish. Symptoms ranged from mild effects
to a moderately severe illness consisting of abdominal cramps,
anorexia and fever. This is the first time that a common-source
outbreak has been proved to be the result of M. conjunctus,
even though the parasite has been reported in central,
northern and eastern Canada and the eastern USA for
decades. This example indicates that such diseases can emerge
through changing eating habits. Certainly, parasitic diseases
originating from fish are under-reported, especially in native
communities. For instance, tapeworm infections from
Diphyllobothrium
appear to be common in native
communities in northern Canada. Since infections invariably
arise from the consumption of raw or incompletely cooked
fish, control is best achieved by thorough cooking.
Costs of illnesses associated
with seafood toxins
Costs to measure the effect of seafood toxins in a community
or nation are not often documented, and those which do exist
tend to be imprecise estimates. There are three types of costs
associated with seafood toxins:
a) loss of product sales because of closure of harvest areas or
embargo of imported products
h) costs of monitoring potentially toxic areas and inspection
and analysis of finished products
c) costs associated with human illness.
Some of these costs have been determined for Canada (5, 2 4 ) .
Only two viral outbreaks associated with seafood have been
recorded. The first outbreak occurred in 1 9 9 1 , when a
number of related episodes, affecting more than 175
individuals, resulted from the ingestion of Norwalk-type
viruses in New Brunswick oysters (Ostrea edulis). The second
In
1 9 8 8 , the
PSP monitoring
programme
cost
CDN$2,300,000, and the medical and lost productivity
costs for the estimated 100 cases were approximately
CDN$850,000. Since all those who become ill are assumed to
668
be recreational harvesters who ignored warning signs, loss
due to adverse publicity is not a significant factor. There has
not been a PSP episode involving commercially-sold shellfish
since 1 9 7 9 . Only one episode of ASP caused by the ingestion
of domoic acid has been documented in Canada. Medical
costs, lost productivity and research costs to identify the toxin
were at least C D N $ 4 , 0 0 0 , 0 0 0 . Losses to growers, wholesalers
and retailers were even greater because of the ban on sales and
public concern for all seafood products. In 1 9 8 8 , the cost of
implementing a domoic acid monitoring programme was
CDN$ 1,390,000. As a result of the effectiveness of the
monitoring programme, no further illnesses or public concern
with regard to ASP has occurred.
There are no specific measures to check shellfish for
diarrhoetic shellfish poison or tetramine, since only one or
two outbreaks have been documented. Scombroid poisoning
cases may cost C D N $ 6 0 0 , 0 0 0 each year. Many fish which are
likely to cause this type of illness (e.g., imported tuna and
mahi-mahi) are analysed for histamines and other spoilage
amines at an annual cost of approximately CDN$27,000.
Ciguatoxin is only found in tropical fish, but because there are
no suitable analytical methods, these fish are not routinely
analysed for the toxin. Ciguatera poisoning is probably
adequately diagnosed in Canada. Based on the assumption
there may be as many as 3 0 0 cases of ciguatera poisoning each
year, either from tourists visiting tropical areas or from
tropical fish consumed in Canada, and assuming that each of
these cases costs CDN$4,000, the total annual cost could be
as high as CDN$ 1,236,000.
Therefore, the total illness-related costs associated with
seafood toxins are CDN$2.7 million, while monitoring and
analytical costs are CDN$3.7 million. In the future, it may be
that ciguatera poisonings will increase and contribute more
costs because of an increased demand for tropical fish and the
lack of a good test method for Ciguatoxin.
Control programmes
Outbreaks in the Bay of Fundy, St Lawrence Estuary and the
Pacific coast led to the initiation of a PSP toxins shellfish
monitoring programme based on mouse bioassay by the DFO
in the 1940s. Improvements to this assay continued until the
implementation of the 1 9 9 4 protocol of the AOAC
International (formerly, the Association of Official Analytical
Chemists). Shellfish from specific areas are sampled and
tested on a schedule based on historic toxicity levels. Surveys
are also performed in areas where there is a potential market
for shellfish harvesting and where the public may carry out
recreational harvesting. Acceptable limits are < 8 0 pg
saxitoxin equivalents (STXeq) per 100 g of raw shellfish soft
tissues and < 160 pg STXeq per 100 g of softshell clams and
mussels to be canned. Areas found to be toxic are closed and
Rev. sci. tech. Off. int Epiz., 16 (2
the public is alerted through the local media and through
warning notices posted on beaches. Since 1 9 8 2 , monitoring
has also been performed along the Newfoundland coast, some
parts of south and east Nova Scotia and the Magdalen Islands
in the Gulf of St Lawrence. Whilst some parts of the east coast
of Canada are closed usually in the summer and autumn
months only, much of the west coast is closed throughout the
year. Monitoring has been performed for domoic acid since
the ASP incident of 1987. A modified PSP mouse bioassay has
been superseded by a more sensitive high performance liquid
chromatography (HPLC) method: the action level for shellfish
is 2 0 µg domoic acid per gram of soft tissue. Monitoring for
PSP and ASP is effective in preventing contaminated products
from reaching commercial trade, but cannot stop recreational
harvesters from fishing in closed areas. There is no official
monitoring programme for DSP, but areas in which past
evidence proves the presence of DTX-1 or okadaic acid (Nova
Scotia and Newfoundland) are sampled in the summer and
autumn months.
The rapid growth of the aquaculture industry has increased
the amount of seafood products, particularly mussels,
reaching markets across North America, and there has been a
corresponding increase in the populations at-risk. Therefore,
continued monitoring of areas known to be sources of toxins
is important. In addition, testing should be performed at
potential new aquaculture harvesting areas, and more rapid
and sensitive detection methods should be developed for
newer toxins. The DFO currently follows up complaints of
identifiable and unknown causes and responds with
appropriate action, including increased monitoring and more
research.
Microbiological testing for organisms indicative of microbial
pathogens in waters from which shellfish are harvested is
performed by the Department of the Environment. Growing
areas with a geometric mean of < 14 faecal coliforms/100 ml
and with < 4 4 faecal coliforms/100 ml in no more than 10%
of the samples are approved for harvesting. Areas with an
average of < 8 8 faecal cofiforms/100 ml and with < 2 3 0 faecal
coliforms/100 ml in no more than 1 0 % of the samples can be
used for harvesting shellfish, provided that all shellfish
harvested are exposed to a depuration step. Areas with counts
higher than those mentioned above are closed to harvesting.
Approved areas are retested at least every three years.
In February 1 9 9 2 , the DFO implemented a Quality
Management Program (QMP) for fish and shellfish inspection.
This was the first mandatory food inspection programme in
the world to be based on hazard analysis and critical control
point (HACCP) principles, and results should show an
increase in the safety of fish and shellfish for consumers. The
QMP was developed through the co-operative efforts of the
fish processing industry and the DFO. The implementation of
the QMP in Canada has been accepted by trading nations to
allow greater access of fish and shellfish products from
669
Rev. sci. tech. Off. int. Epiz, 16 (2)
Canada to foreign markets. The following analyses are
included when evaluating a product during a QMP
inspection:
a) cooked and ready-to-eat products (RTE) are analysed for
Escherichia coli and S. aureus
b) molluscan shellfish are analysed for E. cóli. Where
necessary, chemical analysis for marine toxins will be
undertaken
c) dungeness crabs (Cancer magister Dana, 1 8 5 2 ) are
analysed chemically for marine toxins where necessary
d) aquaculture finfish are monitored for the presence of drug
residues
e) analyses for contaminants are conducted for those species
which represent a potential risk and for new or developmental
fisheries.
The DFO follows the Health Canada policy for Listeria
monocytogenes in ready-to-eat foods, which is based on
HACCP principles and has been developed using a risk
assessment approach (6). The policy directs inspection and
compliance action regarding RTE foods which are capable of
supporting growth of the pathogen: the policy is based on a
combination of inspection, environmental sampling and
product testing. The highest priority is given to those RTE
foods which have been causally linked to listeriosis (Category
1) and to those with a shelf-life which exceeds 1.0 days
(Category 2 ) and an action level of 0 colony-forming units
(CFUs) in the sample taken (25-50 g). Since seafood has
rarely been associated with listeriosis and usually cannot be
refrigerated for over ten days without spoilage occurring, most
products (e.g., frozen cooked lobster tails, fresh oysters and
fresh fish) fall into Category 3, which has an action level of
^ 100 CFU/g. Some fish or shellfish products which have
been linked with listeriosis in various countries include
smoked mussels, shrimp, artificial crab and cold-smoked
rainbow trout species (Salmo gairdneri).
In 1997, the Inspection Directorate of the DFO joined the
former Health Canada and Agriculture and Agri-Food Canada
inspection branches to form the new Canadian Food
Inspection Agency which co-ordinates all Federal control
measures for food in Canada. This will lead to improved
inspection and control of all foods, including fish and
shellfish. Health Canada, in co-operation with the new
Agency, will be developing risk assessments for appropriate
situations. For instance, a risk assessment is currently being
prepared for V. vulnificus in oysters imported from the Gulf of
Mexico.
Conclusion
Although seafood illnesses occur in Canada, efforts are being
made by public health and fisheries officials to document
cases and to prevent recurrences through the use of
appropriate control programmes. With the development of
aquaculture projects, particularly for mussels, the potential for
toxin- or microbial-associated illnesses increases. Fortunately,
the cultured shellfish industry, mindful of the 1 9 8 7 domoic
acid incident, is well aware of the impact of a seafood
intoxication, and co-operates with DFO staff to prevent
contamination of shellfish stock with toxic algal blooms. The
relaying of shellfish or the dumping of ballast water can
spread dinoflagellates and probably enteric pathogens from
one area to another (18). Another possible source of emerging
seafood diseases is the increased exposure to hazards due to
enhanced productivity and the greater availability of more
varieties of fish and shellfish. At the same time, there is a
decrease in the size of the traditional fish stock, which means
that more imported products and different types of local
seafood can be expected to appear on the market in Canada.
This creates the potential for introducing agents into the food
supply. For instance, when the herring stock in the United
Kingdom had decreased to non-harvestable levels, the fishing
industry turned to mackerel as a substitute; this resulted in a
dramatic increase in scombroid fish poisonings because
mackerel spoil more easily than herring and produce
histamine in the flesh (3).
Key factors which allow diseases to emerge are:
a) environmental changes
b) mechanical spreading of infectious or toxic agents through
human activity
c) development of new culturing and fishing procedures,
including the cultivation of previously unused fish and
shellfish
d) social change in eating habits and traditional eating habits
by immigrants from other countries
e) greater awareness by public health personnel of rare
diseases and better ability to detect agents by more specific
and sensitive analytical methods.
Any control programme must address the above concerns in
order to be successful in reducing the number of fish and
shellfish-borne diseases in Canada.
Acknowledgements
Much of the information in this paper was derived from
information collected by the Inspection Directorate of the
Department of Fisheries and Oceans. The co-operation of the
staff is appreciated.
670
Rev. sci. tech. Off. int. Epiz, 16 (2)
Toxi-infections alimentaires dues à la consommation de poisson et
de fruits de mer et leur prévention au Canada
E.C.D. Todd
Résumé
L'intoxication paralysante par des mollusques et crustacés est connue chez
l'homme et étudiée depuis deux siècles ; des programmes de prophylaxie
existent depuis une cinquantaine d'années. Quant à l'intoxication diarrhéique, si
des cas sont signalés presque chaque année, le dernier décès connu date de
1981. Plus récemment, des cas d'intoxication avec effet d'amnésie, de ciguatera,
d'intoxication diarrhéique, d'intoxications par l'histamine (intoxication par les
scombridés) et par la tétramine ont été décrits. L'intoxication par les scombridés,
due à un mauvais stockage du poisson, est la plus fréquemment observée, mais
celles dont les conséquences sont les plus graves sont l'intoxication paralysante
et la ciguatera. Les infections à Vibrio résultant d'une contamination naturelle des
coquillages sont quasiment inconnues et les maladies virales liées à la pollution
des eaux de pêche sont rares. La prophylaxie consiste à surveiller les eaux pour
rechercher des indicateurs d'agents pathogènes pour l'homme. Des systèmes
d'inspection basés sur la méthode de l'analyse des risques, points critiques pour
leur maîtrise sont actuellement instaurés dans toutes les zones de récolte de
poissons et coquillages. La Direction de l'inspection, relevant du Département
des pêches et océans, a été rattachée au nouveau Service canadien d'inspection
alimentaire en 1997, qui coordonne à l'échelle nationale les mesures fédérales
d'hygiène alimentaire.
Mots-clés
Canada - Microbiologie - Poissons et fruits de mer - Prophylaxie - Santé publique Toxines.
Toxi-infecciones alimentarias asociadas a los alimentos de origen
marino y su control en Canadá
E.C.D. Todd
Resumen
Hace dos siglos que vienen describiéndose casos de envenenamiento paralítico
por marisco, para cuyo control se aplican programas desde hace 50 años.
Aunque se comunican nuevos casos de intoxicación prácticamente cada año, la
última muerte por envenenamiento diarreico por marisco de la que se tiene
conocimiento se produjo en 1981. Más recientemente se han descrito casos de
envenenamiento amnésico por marisco, ciguatera, envenenamiento diarreico por
marisco, envenenamiento por escómbridos (toxicidad histamínica) y
envenenamiento por tetraminas. Aunque la enfermedad observada con mayor
frecuencia es el envenenamiento por escómbridos a partir de alimentos
almacenados en condiciones inadecuadas, el envenenamiento paralítico por
marisco y la ciguatera son las dolencias que acarrean las más graves
consecuencias. Son prácticamente desconocidas las infecciones por Vibrio
causadas por marisco infectado de forma natural, y muy raras las enfermedades
víricas provocadas por la contaminación de las aguas de captura. La vigilancia
del agua para detectar en ella indicadores de agentes patógenos para el hombre
671
Rev. sci. tech. Off. int. Epiz., 16 (2)
es el método más seguro de control. En todas las áreas de captura de pescado y
marisco se están introduciendo sistemas de inspección basados en el análisis de
riesgos y control de puntos críticos. La Dirección General de Inspecciones del
Ministerio de Pesca y Océanos se integra en 1997 en el nuevo Organismo de
Inspección de Alimentos (Food Inspection Agency) de Canadá, encargado de
coordinar a nivel nacional todas las medidas federales de protección alimentaría.
Palabras clave
Alimentos de origen marino - Canadá - Control - Microbiología - Salud pública -Toxinas.
•
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