Volume 27-04
15 February 2001

[Table of Contents]

OUTBREAK OF TRICHINELLOSIS ASSOCIATED WITH ARCTIC WALRUSES IN NORTHERN CANADA, 1999

Introduction

Trichinellosis is a widespread helminthic zoonosis endemic in Northern Canada where an estimated incidence rate in the indigenous population is 11 cases per 100,000⁽¹⁾. Infected polar bear and walrus meat have been the most frequent sources of human trichinellosis in the Canadian Arctic although there are other real and potential carnivore sources of human infection^(1-4). Estimates of trichinellosis prevalence rates in polar bear (Ursus maritimus) have ranged from 24.2% to 60.9%, and in walruses (Odobenus rosmarus) from 1% to 4%^(1,4-6) (Proulx JF, Nunavik Regional Board of Health and Social Services, Kuujjuaq: personal communication, 1998). In rarely consumed carnivores, prevalence rates are >= 33% in red foxes (Vulpus vulpes) and wolves (Canis lupus) and up to 36% in arctic foxes (Alopex lagopus)^(7,8).

Trichinellosis in the Arctic is caused by Trichinella nativa which differs from the temperate Trichinella spiralis in its resistance to freezing. T. spiralis and T. nativa species-related differences in clinical presentation have not been described except for those that can be ascribed to the level of human host immunity at the time of infection^(9,10).

Since the first reported walrus-related outbreak in 1982, a number of outbreaks have been reported; the largest one, in 1987, affected 42 individuals and was associated with walrus meat^(1,11,12) (Proulx JF, Nunavik Regional Board of Health and Social Services, Kuujjuaq: personal communication, 1998). The clinical presentation of many of the cases in these outbreaks differed from classic myopathic trichinellosis. The 1987 outbreak showed two distinct syndromes: the classic "myopathic" form with edema, fever, fatigue, and rash; and a "diarrheic" form with a persistent diarrhea illness and little edema or fatigue. Serologic and epidemiologic evidence suggested that the "myopathic form" represented a primary infection while the "diarrheic form" occurs upon re-infection of individuals who have pre-existing immunity to T. nativa⁽¹²⁾.

In this paper, we describe an outbreak of trichinellosis on Baffin Island, 96 kilometers above the Arctic Circle, during the months of August-September 1999. This is the most northern outbreak of walrus-source trichinellosis yet described in Canada.

Methods

During the month of September 1999, seven individuals from the community of Qikiqtarjuaq, an arctic community on the east coast of Baffin Island, consulted the local nursing station for diarrhea, abdominal pain, fatigue, rash and/or swelling. All seven individuals had eaten raw meat from at least one of three walruses 2 to 4 weeks earlier. A local radio summons was made by the nursing station, requesting that all individuals who had eaten these walruses, report to the nursing station for clinical and laboratory evaluation.

Eosinophil counts were performed locally and sera were sent to the National Centre for Parasitology (Serology) of McGill University for Trichinella antibody detection. Trichinella serology was performed with an enzyme linked immunosorbent assay (ELISA) technique (Alexon Trend, California) using an excretory-secretory antigen^(13,14). Using this assay, a serum is considered seropositive for Trichinella if the optical density (OD) is >= 0.30, and is highly positive if the OD is >= 1.20.

A case of trichinellosis was diagnosed if, 1) an individual with at least one clinical symptom compatible with trichinellosis (edema, muscle pain, or diarrhea) had positive serology (OD >= 0.30) for trichinellosis and/or eosinophilia (>= 15% of white blood cell count) or 2) an individual with no clinical symptoms who had both a positive serology for trichinellosis (OD >= 0.30) and eosinophilia (>= 15%)⁽¹⁾.

Confirmatory testing of walrus meat was conducted at the Centre for Animal Parasitology, Canadian Food Inspection Agency, Saskatoon, using a previously described pepsin-HCl digestion method incorporating a double separatory funnel sedimentation step to recover larvae⁽¹⁵⁾. The assay was modified for testing walrus tissues by increasing digestion times and the ratio of digestion fluid to sample size.

Results

Sixty-two Inuit in the Qikiqtarjuaq community ate meat from at least one of three harvested walruses. Among the originally diagnosed cases, the predominant symptoms were fatigue (7) and diarrhea (6) that persisted an average of 18 days or until the patients received treatment with mebendazole. All seven had high levels of Trichinella antibodies (average OD of 3.00). Eosinophil levels averaged 23% (range 5% to 64%) of total peripheral leukocytes.

Three samples of walrus meat, recovered from two families, were tested using the digestion/sedimentation method. The samples were positive with counts of 4, 16 and 19 larvae/gm.

Subsequent to the appearance of the initial group of seven cases, the local radio appeal recruited a further 55 Inuit who indicated they had eaten raw walrus meat from the suspect walruses within the previous 3 to 6 weeks. The general profile of these individuals is summarized in Table 1. The mean age of the walrus eaters was 43.2 years; 14.5% were < 21 years of age, and 19.3% were > 60 years old. There was also a predominance of women among the evaluated walrus eaters (male:female ratio = 0.40).

Table 1 Clinical profile of 62 Inuit who ate walrus, Qikiqtarjuaq, August to September 1999
	Trichinellosis cases (%)	Non-cases (%)
Number	34 (54.8)	28 (45.2)
Average age (years)	41.7 (±18.6)	45.0 (±20)
Male:female ratio	0.65	0.18
Clinical symptoms Diarrhea Edema Fever Rash Muscle pain Fatigue	17 (50.0) 5 (14.7) 6 (17.6) 11 (32.4) 16 (47.0) 16 (47.0)	2 (7.1) 1 (3.5) 3 (10.7) 0 (0.0) 1 (3.5) 3 (10.7)
Laboratory data Eosinophilia >= 15% IgG level >= 0.30 IgG level >= 1.20	25 (73.5) 30 (88.2) 26 (76.5)	0 (0.0) 10 (35.7) 3 (10.7)

Of the 62 individuals who consumed raw walrus meat, the attack rate of clinical trichinellosis was 55% (34/62) (Table 1). Twenty-six of the 34 (76%) met the first case-diagnosis criterion and eight (24%) met the second criterion. Diarrhea, fatigue, and muscle pain were the pre-dominant clinical symptoms. The percentage of seropositivity among the clinical cases was high (30/34; 88%) and of the 30 seropositive cases, 26 had high levels of antibodies (OD >= 1.20). A total of 28 walrus consumers did not meet the trichinellosis case criteria. Among these non-cases (Figure 1), 7% had diarrhea, 3% had edema, 3% had muscle pain and 10% had fever or fatigue. None of them had eosinophilia while 35% had a low titre of Trichinella antibodies and 10% had high titres. Most of the non-cases were females (ratio male:female = 0.18).

All cases that had eosinophilia (>= 15%) were diagnosed as clinical trichinellosis and 84% of these eosinophilic cases had very high titres of IgG anti-Trichinella (OD >= 1.20).

In trichinellosis cases, high levels of eosinophilia were noted at both extremes of antibody titre. In non-cases there were no instances of eosinophilia; 64% of these had negative antibody titres (Figure 1). Eighty-eight percent of cases had had a positive serology, as did 36% of non-cases. The titre distribution can be seen to clearly distinguish the two groups (Figure 1).

All cases that presented with symptoms or who were found to have eosinophilia were treated with mebendazole according to a local protocol for trichinellosis outbreaks (5 mg/kg twice daily for 10 days).

Discussion

Walrus is the most important source of human trichinellosis in the Arctic of the Western Hemisphere. Large outbreaks of human trichinellosis of walrus origin have been described since 1948 with outbreaks widely dispersed from Barrow Point, Alaska to Disco Bay, Greenland^(4,5,16). Walrus-related trichinellosis in Canada has only been reported in Nunavik (northern Quebec) and Nunavut where the walrus harvest is an important source of food. Walrus-related trichinellosis outbreaks have occurred as far south as Inukjuak on Hudson Bay and as far north as Saluit although it is presumed that the high prevalence of Trichinella antibodies or intradermal test positivity further north in Southampton Island, Igloolik, Cape Dorset and Spence Bay reflect infected walrus consumption^(17-19). Raw walrus consumption is common and bear consumption is rare in the Inuit populations in these regions.

The outbreak is remarkable in being the most northern described to date in Canada. It is not possible to determine how many of the three walruses were Trichinella infected as there is no routine testing of harvested walruses in this region. The walrus meat is divided up among the community soon after harvest so that individual walruses can not be identified subsequently. The attack rate of 55% is compatible with a singly infected walrus that everyone ate, but is also compatible with two or more infected walruses. In a 1997 outbreak in Inukjuak on the east coast of Hudson Bay, two of five harvested walruses were infected (Proulx JF, Nunavik Regional Board of Health and Social Services, Kuujjuaq: personal communication, 1998). Prevalence rates in past walrus surveys in the Eastern Arctic have been £ 5%, and the most recent survey, the Nunavik Trichinellosis Prevention Program in Northern Quebec, tested 198 harvested walruses between 1982 and 1999 and found only 2.5% infected⁽²⁰⁾. However surveys east of Greenland, in the Norwegian and Barents Seas, revealed a prevalence rate of 7%⁽²¹⁾. Larger surveys are required to determine if the prevalence of trichinellosis in walruses is increasing in Canada.

In the most populous regions of Canada, effective programs for the elimination of trichinellosis from domestic swine have been developed, leading to a decrease in its incidence⁽²⁾. However, it is impossible to control the etiologic agent in areas such as the Arctic, where diverse populations of infected wild carnivores are common food sources, and trichinellosis remains a significant threat to public health. There have been a few control and prevention programs for trichinellosis in the North, based on the inspection of meat and education of the community, but these programs remain limited and have not yet been applied to the Baffin Region or other areas at risk in northern Canada⁽²⁰⁾.

This community consists of approximately 500 inhabitants, 95% of whom are Inuit and the ratio of males:females is almost equal. Hunting of seal, narwhal and walrus and fishing for char are important parts of daily life. From April to June walruses are hunted at the ice floe edge 100 to 150 miles away and in August to October by boat, 50 miles away. The raw meat is stored (fermented) under rock caches and then, several months later, shared (uncooked) by the community. Walrus consumption is more frequent in older Inuit⁽¹¹⁾. In this outbreak cases ranged in age from 6 to 77 years of age with only 14.5% being < 21 years of age.

The arctic species of Trichinella (T. nativa) is resistant to freezing temperature and in some animal models is more enteropathogenic and less muscle invasive than the other temperate strains^(22,23). T. nativa isolates have remained viable at -10° C to -20° C for 4 years⁽²²⁾. While freezing is a readily available form of storage in the Arctic, the Trichinella infected walruses in this outbreak were caught in the Spring ice-edge hunt and were not frozen between hunt and consumption.

Among non-cases, 36% had a positive antibody titre. In a systematic survey in one community in the Arctic, Trichinella sero-prevalence was 19.6%⁽¹¹⁾. It is possible that the 36% represents both this background prevalence and cases of Trichinella infection that did not develop sufficient clinical and/or laboratory abnormalities, during this outbreak, to meet the case definition for trichinellosis. However, none of these sero-positive non-cases had eosinophilia. This study confirms the usefulness of eosinophilia as an easily available marker of clinical trichinellosis in a northern setting where other helminthes (Diphyllobothrium sp., Enterobius, Echinococcus granulosis) are not associated with such levels.

Although prolonged-diarrhea trichinellosis is common in the Arctic (diarrhea occurred in 50% of persons in this outbreak), the complete duration of symptoms was not recorded and therefore the frequency of prolonged-diarrhea trichinellosis and the short-term diarrhea seen in classical/myopathic trichinellosis cannot be determined^(1,11,12). The attack rate was 55% and the incubation period was 10 to 15 days; both consistent with previous Arctic outbreaks^(11,12,24).

The continuing outbreaks of trichinellosis in northern Canada in native communities and the evolving Trichinella Prevention Program in northern Quebec demonstrate the importance of maintaining trichinellosis as a reportable zoonotic disease in humans.

References

1. MacLean JD, Viallet J, Law C et al. Trichinosis in the Canadian Arctic: report of five outbreaks and a new clinical syndrome. J Infect Dis 1989;160:513-20.

2. Appleyard G, Gajadhar A. A review of trichinellosis in people and wildlife in Canada. Can J Public Health 2000;91:293-7.

3. Zarnke RL, Gajadhar AA, Tiffin GB et al. Prevalence of Trichinella nativa in lynx (Felis lynx) from Alaska, 1988-1993. J Wildl Dis 1995;31:314-8.

4. Forbes LB. The occurrence and ecology of Trichinella in marine mammals. Vet Parasitol 2000;93:321-34.

5. Rausch RC. Trichinosis in the arctic. In: Gould SE, ed. Trichinosis in man and animals. Springfield, Illinois: Charles C Thomas, 1970;340-73.

6. Larsen T, Kjos-Hansen B. Trichinella sp. in polar bears from Svalbard, in relation to hide length and age. Polar Research 1983;1:89-96.

7. Rausch R, Babero BB, Rausch RV et al. Studies on the helminth fauna of Alaska. XVII. The occurrence of larvae of Trichinella spiralis in Alaskan mammals. J Parasitol 1956;42:259-71.

8. Prestrud P, Stuve G, Holt G. The prevalence of Trichinella sp. in Arctic foxes (Alopex lagopus) in Svalbard. J Wildl Dis 1993;29:337-40.

9. Britov VA, Boev SN. Taxonomic rank of various strains of Trichinella and their circulation in nature. Westn Akad Med Nauk SSSR 1972;28:27-32.

10. Pozio E, La Rosa G, Murrell KD. Biological characterization of Trichinella isolates from various host species and geographical regions. J Parasitol 1992;78:647-53.

11. Viallet J, MacLean JD, Goresky CA et al. Arctic trichinosis presenting as prolonged diarrhea. Gastroenterology 1986;91:938-46.

12. MacLean JD, Poirier L, Gyorkos TW et al. Epidemiologic and serologic definition of primary and secondary trichinosis in the Arctic. J Infect Dis 1992;165:908-12.

13. Ivanoska D, Cuperlovic K, Gamble HR et al. Comparative efficacy of antigen and antibody detection tests for human trichinellosis. J Parasitol 1989;75:38-41.

14. Wilson M, Ware DA, McAulay JB. Comparison of the CDC bentonite floculation test with the LMD ELISA kit for detection of antibodies to Trichinella spiralis. Presented at the Annual meeting of the American Society of Tropical Medicine and Hygiene, Boston: 1991.

15. Forbes LB, Gajadhar AA. A validated Trichinella digestion assay and an associated sampling and quality assurance system for use in testing pork and horsemeat. J Food Prot 1999;62:1308-13.

16. Thorberg NB, Tulinius S, Roth H. Trichinosis in Greenland. Acta Pathol Microbiol Scand 1948;25:788-94.

17. Brown M, Sinclair RG, Cronk LB et al. Intestinal parasites of Eskimos on Southampton Island, Northwest Territories. Can J Public Health 1948;39:451-54.

18. Brown M, Green JE, Boag TJ et al. Parasite infections in the Eskimos at Igloolik, N.W.T. Can J Public Health 1950;41:508-12.

19. Davies LEC, Cameron TWM. Trichinosis in the Northwest Territories. Med Serv J Can 1961;17:99-104.

20. Proulx JF, Leclair D, Gordon S. Trichinellosis and its prevention in Nunavik, Quebec, Canada. Arctic Med Res (in press).

21. Thorshaug KN, Rosted AF. Researches into the prevelence of tricinosis in animals in arctic and antarctic waters. Nord. Vet Med 1956;8:115-29

22. Handeland K, Slettbakk T, Helle O. Freeze-resistant Trichinella (Trichinella nativa) established on the Scandinavian peninsula. Acta Vet Scand 1995:36;149-51.

23. Kapel CM, Pozio E, Sacchi L et al. Freeze tolerance, morphology, and RAPD-PCR identification of Trichinella nativa in naturally infected arctic foxes. J Parasitol 1999:85;144-7.

24. Margolis HS, Middaugh JP, Burgess RD. Arctic trichinosis: Two Alaskan outbreaks from walrus meat. J Infect Dis 1979;139:102-5.

Source:  B Serhir, PhD, JD MacLean MD, National Centre for Parasitology (Serology), McGill Centre for Tropical Disease, Montreal General Hospital; S Healey, MSc, B Segal, BSc, Public Health Nurses, Department of Health and Social Services; L Forbes, DVM, Nunavut; Centre for Animal Parasitology, Canadian Food Inspection Agency, Saskatoon, Saskatchewan.

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