Epidemiology of Giardiasis in Tasmania:
A Potential Risk to Residents and Visitors
jennqer S. Kettlewell, Silvana S. Bettiol, Norman Davies,
El Milstein, andjohn M . Goldsmid
Background: Giardia infection is an ongoing problem inTasmania and occurs throughout the state. It has been postu-
lated that part of the problem is the reservoir of infection in native animals which is suggested to contribute to infections
i n humans.To date, however, no detailed study on the epidemiology of giardiasis inTasmania has been carried out.
Methods: Information regarding the prevalence of Giardia infection i n humans and the risk of intrafamilial transmission
was obtained from the Department of Community and Health Services and from the direct examination of human or
animal fecal samples.
Results: Giardia has been found to be present i n a wide range of native and domestic animals and i n humans of all ages
from all over the state.
Conclusions: Giardiasis is endemic inTasmania and poses a risk to locals as well as to visitors to the state, especially
those who participate i n wilderness activities such as bushwalking.These people must be aware of the possible risk of
Giardia infection and should take precautionary measures to avoid infection.
natural beauty and reputation as a holiday destination for
keen bushwalkers is often marred by “bushwalker’s diarrhea,” for which Giardia duodenalis is frequently blamed.
Goldsmid et al.3 first demonstrated C. duodenalis as an
intestinal pathogen in Tasmanian communities, with
strong suggestions of familial transmission.The prevalence
of Giardia spp. in Tasmanian native marsupial populations
has been estimated to be as high as 21%.4
In Australia, Giavdia duodenalis is the most commonly reported intestinal parasite of human populations.’ G. duodenalis has been isolated from 2-3% of
patients suffering from diarrhea statewide.“’ Epidemic
outbreaks of the infection are thus, not surprisingly,
recorded from time to time in daycare centres and similar environments which are conducive to facilitating
person-to-person tran~mission.~
T h e prevalence of
G. duodenalis infection is even higher in refugees, immigrants, and returned travelers from developing countries to Tasmania, reaching levels as high as 11%.9-11
Giardiasis thus poses a particular risk to tourists and
those pursuing outdoor activities such as bushwalking.
What then is the risk of Giardia infection of visitors to Tasmania, and what external factors are involved?
In this study, we investigated the epidemiology of giardiasis in relation to factors predisposing to human infection in the state as well as tendency toward familial
transmission. Additionally, since the acceptance of
giardiasis as a zoonosis,’2 interest in the range of aniIn Tasmal hosts harboring G. duodenalis has in~reased.’~
mania, we tested for the infection parasitologically
using trichrome stains, concentration techniques, and
antigen detection in the form of the CELISA kit, for
Tasmania is a temperate island state situated south
of mainland Australia. The island topography includes
mountains, lakes and forests, with almost 30% of its land
mass designated as World Heritage Area, national parks
and reserves. Tasmania remains economically reliant on
agricultural production, but for several years now its
tourist industry has flourished as one of Australia’s most
diverse holiday destinations. As its most attractive feature,
Tasmania offers a wide variety of wdderness activities used
by locals as well as overseas visitors, the most popular of
which is hiking through wilderness areas, an activity
known locally as bushwalking.
As a holiday destination, Tasmania appears to offer
a safe environment due to its pristine image. At one stage,
Tasmania was classified as an area of moderate risk or
unknown status for the acquisition of traveler’s diarrhea.’ Although this claim was rehted by Goldsmid: there
is a risk of Giardia infection in the state. Tasmania’s
Jennifer S. Kettlewell, BSc, Tal Milstein, ESc (Hons), Silvana S.
Bettiol, BSc (Hons), and John M. Goldsmid, PhD: Division of
Pathology, University ofTasmania, Hobart,Tasmania,
Australia; Norman Davies, M.Med Sci: Commonwealth Serum
Laboratories Ltd., Perth, Western Australia.
We acknowledge theTasmanian Parks and Wildlife Service
for financial support.
Reprint requests: Professor John M. Goldsmid, Division of
Pathology, University ofTasmania, 43 Collins Street, Hobart,
Tasmania, Australia, 7000.
JTravel Med 1998; 5:127-130.
127
J o u r n a l of Travel M e d i c i n e , Volume 5, N u m b e r 3
128
a range of domestic and companion animals as well as
for native Tasmanian marsupial species.
Materials and Methods
Human Infection
Information on the seasonal and regional distribution of human Giardia infections in the state,together with
details of patient age and sex, was obtained from the
Department of Community and Health Services, to
whom pathology laboratories report all confirmed cases.
Assessment of intrafadal infection rates was undertaken by stool examination of all f a d y members of eight
index cases, using both parasitologic and antigen detection methods. The family members investigated were
referred to our laboratory by the physician in charge of
the index cases. Fecal samples were then provided by local
pathology laboratories.
To collect data on Giardia infection in bushwalkers, a letter was placed in the Newsletter of the Royal
Australian College of General Practitioners in Tasmania. The letter requested physicians to provide information on laboratory-confirmed cases of giardiasis in
bushwalkers.
Animal Fecal Samples
Four hundred and fifty-six fecal samples were collected from around the state, either from trapped animals
or fresh fecal samples on the ground, and placed into a
sterile sample container until examination. Dog and cat
feces were regularly collected from urban and rural areas
and from boarding kennels.
Fecal Examination
All specimens were examined for the presence of
Giardia using a combination of trichrome staining, formalin-ethylacetate sedimentation c ~ n c e n t r a t i o nand
'~
antigen detection (Giardia CELISA). The formalinethylacetate sedimentation concentration technique was
implemented using the Johns Parafilter System (Biolab
Scientific Pty. Ltd.). Concentrated specimens were examined microscopically with a drop of iodine. As Giardia
cysts are passed at irregular intervals, thus requiring
repeat stools for diagnosis, microscopic methods on single stool specimens are inaccurate. Therefore, the microscopic parasitologic techniques were supplemented with
a method for detecting Giardia antigen in fecal samples.
Each specimen was thus additionally examined for Giardia antigens using a commercially available ELISA kit,
Giardia CELISA (Cellabs Diagnostics Pty. Ltd.). All
specimens were tested according to the manufacturer's
guidelines.
Results
Human Infection
Data from the Department of Community and
Health Services are presented in Figures 1 and 2. Figure
1 shows the seasonal distribution for Giardia infections.
No seasonal trend is evident in this data, but data indicates that giardiasis may be encountered at any time of
the year in the state.
Age distribution reveals infection in subjects ranging in age from less than 1 year to 81 years of age (Fig.
2). The trend appears to be a higher rate of infection in
young children,which decreases in teenage years and early
twenties, followed by another rise in rate at 30-40 years
old which slopes downward as subjects become elderly.
Regression analysis indicated that this is a real, although
only marginally significant, trend.
The sex ratio for the 112 cases recorded for 1996/97
proved equal, with 51% males and 49% females being
diagnosed with giardiasis. Cases of giardiasis were diagnosed widely over the state, with approximately 65% from
urban and 35% from rural areas (despite the fact that the
rural population makes up only 28% of the total Tasmanian population).
The study of giardiasis within f a d y groups revealed
that in seven of eight families of laboratory-confirmed
index cases, other members of the family were also
infected. Of family members screened, 26 of 30 (86.7%)
were also infected with Giardia.
The response from physicians regarding patients
with bushwalker's diarrhea was disappointing. We received
information only for 3 people who had been investigated
for diarrhea after a bushwalkmg expedition and were confirmed by laboratory investigation to be infected with
Giardia. N o other recognized etiologic agents of diarrhea
were isolated from these patients.
14
7
12
10
v1
$
0
W 1996
V
B
6
2
4
2
0
Figure 1 Seasonal distribution of Giardiaduodenalis infections
in Tasmania. Data for March 1995 to December 1997 from the
Department of Community and Health Services, Tasmania.
129
K e t t l e w e l l e t al., G i a r d i a s i s i n T a s m a n i a
strong bushwalking culture and wilderness activities in
*
2
1
1
20-30 age group suggests these activithe state by the
.
10
total
0
z
4
m
.
0
20
40
mmm m
60
80
100
Age (years)
Figure 2 Age distribution for
1995-Fe bruary 1997.
G. duodenalis for March
Animal Fecal Samples
The prevalence of Giardia in native animals as well
as domestic dogs, cats and feral cats is given in Table 1.
The prevalence of Giardia in native animals was found
to be as high as 62%, in bandicoot populations, and as
low as 6%, in the Tasmanian devil and other members
of Dasyuridae. The prevalence of Giardia in dogs and cats
tested was as high as 20%.
Discussion
Giardia duodenalis is a common cause of diarrhea in
Tasmania. The data from the Department of Community and Health Services reveal that G. duodenalis is present throughout the state, associated with diarrhea in a
range of people from the very young to the very old, in
both males and females throughout the year in both
urban and rural areas. Infection tends to be familial, due
to infection within the family unit or from a common
source of infection.
The peaks ofprevalence in young children and in the
20-30 age group suggest several factors. The infection of
young chddren can be spread by person-to-person in daycare centers and similar institutions, and possibly children
with diarrhea are more likely to be taken to a doctor. The
lahle 1 Prevalence of Giardia in Animals in Tasmania
Examined by Microscopy and Antigen Detection on Stool
Specimens
Sample
Animal
Bandicoot
Potoroo
Pademelon
Wombat
Wallaby
Possum
Tasmanian devil (& other Dasyuridae)
Domestic dogs
Domestic & feral cats
Total
Size
Prevalence
(No.)
PA)
26
7
13
62
29
23
35
93
89
32
80
20
19
81
456
16
6
19
20
ties may contribute to infection or, alternatively,the age
group may comprise the parents of children infected in
daycare centres. The response from physicians about
patients with bushwalker’s diarrhea was disappointing.
Physicians frequently assume that bushwalker’s diarrhea
is caused by Giardia infection and therefore treat it empirically with no laboratory confirmation. At this stage there
is still no published evidence to support their claim.
If we accept Giardia as the primary parasitologic
cause of diarrhea in the Tasmanian community, with
strong evidence that it may be the primary cause of
bushwalker’s diarrhea, what is the reservoir for Giardia in
Tasmania? It seems possible that native animals are acting as a reservoir for Giardia, particularly in rural areas.
This study indicates that Giardia is present in a wide
range of native marsupial species, as well as domestic and
companion animals.
The Giardia CELISA, when conducted on samples
from dogs, was shown to have a slightly lowered specificity (95%) and a markedly lowered sensitivity
(55-64%).15 A recent evaluation of the use of kits available in the United States on a range of wild and laboratory animalsI6 concluded that “some commercial
Giardia antigen detection tests are acceptable for animal
testing.” It thus seems reasonable to assume good specificity but a lowered sensitivity, implying infection rates
recorded in the present study may be underestimated.
Overall, the results indicate a significant level of Giardia
being carried in a wide range of animal species.
The finding that cats and dogs act as carriers of Giardia is particularly significant because of their close contact with humans. In addition, they may provide
opportunities for infection of native animals as these
introduced species encroach on previously Giardia-free
habitats. Native animals may have the ability to amplifji
the presence of Giardia in their environment. These animals, once infected by a small number of cysts, could
potentially go on to shed large numbers of cysts over the
period of their infection. The cysts, if they are acquired
directly by other animals or if they make their way into
local water supplies, may then result in further infection.
As the presence of Giardia in the environment increases,
the risk of human infection will show a corresponding
increase.
A preliminary study using flow cytometry reported
isolating Giardia from Tasmanian water samples, and
commented that “Giardia was found in only 5 mainland
water samples, but in 10 Tasmanian samples.”” The
probable route of infection in rural areas, and especially
for bushwalkers, would therefore seem to be water contaminated with human and/or animal feces. This role of
water in Giardia transmission is perhaps not surprising
130
as the natural water in Tasmania tends to be colder than
in the mainland states of Australia, and Giardia is known
to survive best at temperatures below 8"Cf8Furthermore,
this implies that rivers, dams, lakes and other natural
water bodies in Tasmania could become ideal reservoirs
of Giardia as could urban reservoirs. The water could serve
as reservoirs even when the water is chlorinated, Giardia cysts being known to be resistant to standard levels
of chlorination."
It is not known whether the strains of Giardia in animals are identical to those infecting humans, or how the
animals initially became infected. A further possibility is
that human intrusion and defecation in wilderness areas
may spread the infection to native animals. However, it
may be that the animals were infected prior to human
encroachment into these areas. The possibility of native
animals becoming infected with Giardia of human origin has been highlighted by the experimental infection
of a captive Eastern barred bandicoot (Perameles gunniq
with Giardia cysts isolated from human feces4This work
revealed that native animals can easily become infected
with human strains and this, together with the apparent
prevalence of Giardia in native animal species, supports
the hypothesis of cross-species infection.
Many epidemiologic details still require elucidation. While it has been shown that Giardia of human origin can infect animals4and that Giardia of animal origin
can infect humans,2"it remains necessary to establish what
strains of Giardia are present in both humans and animals
in Tasmania to provide evidence to support or invalidate
the hypothesis that transmission between species is occurring. The present work highlights the potential for infection of bushwalkers in the state.
At the present time, the link between human and
animal infection in the state is largely speculative. Additional work is necessary to elucidate details, but it is
advisable for bushwalkers and visitors to the state who
plan to
to be aware Of potential risks and
to undertake steps to minimize them. Bushwalkers are
at special risk of infection with Giardia, which is a recognized etiologic agent for traveler's diarrhea'' and in Tasmania is at least one component of the bushwalker's
diarrhea syndrome. As water is the most likely mode of
transmission, bushwalkers are encouraged to practice
high levels of bush hygiene to prevent spread of the infection, and are advised to boil water taken from even the
most remote streams in the state before consumption.
Acknowledgments
Many thanks to Michael Driessen and The Tasmanian Parks and Wildhfe Service for financial support; to Mr.
David Coleman at the Department of Commumty and
J o u r n a l of T r a v e l M e d i c i n e , V o l u m e 5, N u m b e r 3
Health Services for providing Giavdia statistics,and to Mr.
Peter Ball at the Department of Psychology for his help
with statistical analysis.
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