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Trichinosis -- Maine, Alaska

In 1985, the following outbreaks of trichinosis were reported from Maine and Alaska.

Maine. On October 10, 1985, two cases of trichinosis were reported to the Maine Bureau of Health. The patients had consumed pork from a sow purchased from a local farm. Because members of several families had consumed pork or viscera from the pig, the cases were investigated to determine the extent of the outbreak. A survey was undertaken seeking a history of symptoms commonly seen with trichinosis (fever, myalgias, periorbital edema, and malaise) in individuals known to have consumed the implicated pork. Blood was collected from each individual for eosinophil count and Trichinella serology. A case was defined as an individual with a history of ingesting the implicated pork and with signs and symptoms compatible with trichinosis and either (1) an elevated eosinophil count (total eosinophil count of greater than 450 or a differential greater than 5% on the white blood cell count) or (2) serologic proof of trichinosis infection (bentonite flocculation titers (BF) greater than or equal to 1:5).

Nineteen individuals consumed pork from the implicated pig. Follow-up could not be obtained on three. Two (18%) of the 11 individuals submitting convalescent sera, both with symptoms and elevated eosinophil counts, had titers of 1:10 or greater. Sera drawn during the acute phase on these two patients tested negative. Five (31%) persons met the case definition, with eosinophilia and at least one of the following symptoms: fever (two (40%) individuals), periorbital edema (two (40%)), myalgias (two (40%)), malaise (two (40%)), diarrhea (two (40%)), and maculopapular rash (one (20%)), including both those with positive serologies.

Patients' ages ranged from 25 years to 49 years (mean 35 years). Four (80%) were male. Since all but one individual consumed the implicated pork on more than one occasion, the incubation period could not be determined. All five patients denied consuming the pork raw or undercooked; three were involved in butchering the pig; two were hospitalized and received thiabendazole. The patient with the maculopapular rash received corticosteroids and benadryl. All five patients recovered.

Meat samples from the implicated pig were examined by the Animal Parasitology Institute, U.S. Department of Agriculture (USDA). Analysis by tissue digestion revealed greater than 300 trichinae larva/gram. Investigation by the Maine Bureau of Health of the farm where the pig had been purchased revealed that the farmer fed the pigs garbage (reportedly boiled) and that the environment was conducive to the proliferation of rats. The three remaining pigs at the farm had serologic evidence of trichinosis on testing by USDA. Because approximately 25 suckling pigs were reportedly sold from the farm, a press release was issued November 5 alerting area residents to the problem and asking persons who felt they may have been exposed to noncommercial pork to call the Bureau of Health. To date, no calls have been received, but surveillance is continuing.

Alaska. On March 15, 1985, a private physician reported a case of trichinosis to the Alaska Department of Health and Social Services. Because the patient and 15 other individuals had consumed grizzly bear meat at a birthday party in January 1985, an investigation was initiated similar to the one in Maine.

Follow-up information was obtained from 14 (88%) of the 16 individuals who attended the birthday party and three others who consumed some of the meat either before or after the party. Fourteen (82%) of the 17 had elevated eosinophil counts ranging from 3% to 63%. Of these, nine had the following symptoms suggestive of trichinosis: myalgias (six (67%)), diarrhea (four (44%)), rash (three (33%)), fever (three (33%)), and periorbital edema (one (11%)). BF testing of sera drawn from the 17 individuals 3 months after consumption of the bear meat was negative, except for the index patient who had a titer of 1:20.

The nine patients with eosinophilia and symptoms ranged from 3 years to 35 years of age (mean 22 years). Five (56%) of the patients were female. The incubation period ranged from 10 days to 61 days.

The implicated bear meat had been frozen for approximately 3 weeks before the party. The frozen meat was cut into bite-sized pieces and reportedly cooked in a soup with vegetables for 1-2 hours. No samples of the meat were available for examination or for verification of cooking status. Reported by E Lommler, MD, Millinocket Regional Hospital, M Boulanger, MD, Lewiston, D Dineen, DVM, Maine Dept of Agriculture, C Allen, KF Gensheimer, MD, State Epidemiologist, Maine Bureau of Health; SA Jenkerson, Nurse Epidemiologist, Epidemiology Office, J Middaugh, MD, State Epidemiologist, Alaska Dept of Health and Human Svcs; KD Murrell, PhD, Animal Parasitology Institute, US Dept of Agriculture; Helminthic Diseases Br, Div of Parasitic Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Although the incidence of trichinosis has decreased markedly from 300 to 400 cases reported annually in the late 1940s (1) to a mean of 88 cases reported annually over the past 5 years, trichinosis remains a public health problem in the United States. The outbreaks presented here highlight interesting aspects of the epidemiology and control of trichinosis. A large number of the cases reported each year occur in the New England and Middle Atlantic states, a finding that has been associated with the high concentration of ethnic groups in those regions whose culinary preferences include raw pork (1). In addition, recent studies suggest that swine from these regions may be more highly infected than those of other regions. Surveys of selected slaughterhouses in the New England and Middle Atlantic states found infection rates of 0.73% and 0.58%, respectively (2,3), surpassing the estimated national average rate of 0.1% (4). These findings were attributed to certain swine-management practices (garbage feeding, rat infestation ((5)), and cannibalism) by small and/or part-time hog producers common to these regions. In light of the culinary preferences of the resident ethnic groups of these areas, the relative importance of these findings needs further investigation.

This is the fifth outbreak of trichinosis reported from Alaska since 1975 (6). Two outbreaks have involved walrus meat; one, black bear meat; and two, including the one reported here, grizzly bear meat. Epidemiologic and experimental studies suggest that the arctic strain of T. spiralis may be more resistant to cold than those found in pork. According to USDA recommendations, T. spiralis in pork is rendered nonviable if held at -15 C (5 F) (temperatures achievable in noncommercial refrigerators) for 20 days. However, polar bear meat, stored at -18 C (0 F) for up to 24 months remained infective for mice (7,8), and an outbreak of trichinosis resulted from the consumption of bear meat frozen for 81 days at -18 C (0 F) (9). Since control of trichinosis, in part, has relied upon the widespread use of commercial and home freezing (1), this difference between strains is of clinical importance and needs to be emphasized through public health education to potential consumers of wild animal meat. However, adequate cooking at 77 C (170 F)--well above the thermal death point of the parasite--remains the best safeguard against trichinosis.

References

  1. Schantz PM. Trichinosis in the United States--1947-1981. Food Tech 1983;83-6.

  2. Schad GA, Leiby DA, Duffy CH, Murrell KD. Swine trichinosis in New England slaughterhouses. Am J Vet Res 1985;46:2008-10.

  3. Schad GA, Kelly M, Leiby DA, Blumrick K, Duffy CH, Murrell KD. Swine trichinosis in mid-Atlantic slaughterhouses: possible relationship to hog marketing systems. Prev Vet Med (in press).

  4. Zimmerman WJ, Zinter DE. The prevalence of trichinosis in swine in the United States 1966-1970. HSMA Health Rep 1971;86:937-45.

  5. Murrell KD, Gamble HR, Schad GA. Experimental transmission of Trichinella spiralis to swine by infected rats. Procedings Helminthol Soc Wash 1984;51:66-8.

  6. CDC. Trichinosis surveillance annual summary 1981. Issued October 1982.

  7. Kjos-Hanssen B. Freeze resistance of Trichinella cysts in polar bears from the high-arctic region of Norway (Svalbard). Acta Vet Scand 1983;24:244-6.

  8. Kjos-Hanssen B. Trichinella isolates from polar bears in Svalbord. Freeze resistance and infectivity in rats and swine. Nord Vet Med 1984;36:57-61.

  9. Clark PS, Brownsberger KM, Saslow AR, Kagan IG, Noble GR, Maynard JE. Bear meat trichinosis. Epidemiologic, serologic, and clinical observations from two Alaskan outbreaks. Ann Intern Med 1972;76:951-6.



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