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Undercooked walrus meat causes two trichinellosis outbreaks in Alaska
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State and federal investigators alerted health care providers in Alaska about two outbreaks of trichinellosis that were caused by the consumption of raw or undercooked walrus meat.
The outbreaks occurred in two communities around Norton Sound in the western part of the state, according to a report in MMWR. All 10 patients — five in each outbreak — fully recovered. They consumed either raw walrus meat or meat that was pan-fried or boiled to a doneness that did not kill the parasite that causes trichinellosis, according to the report by Louisa Castrodale, DVM, MPH, veterinary epidemiologist in the Alaska Division of Public Health (ADPH), and colleagues.
It was the first time since 2002 that walrus meat — once a common source of trichinellosis in Alaska — was linked to a human infection, and the first time since 1992 that it caused an outbreak, Castrodale and colleagues said.
“Health care providers should inquire about consumption of commercially prepared and personally harvested meats when evaluating suspected trichinellosis cases, especially in areas where consumption of wild game is commonplace,” they warned.
Two outbreaks
Alaska Natives are permitted to harvest otherwise protected marine mammals for subsistence purposes, and many coastal communities in the northern and western parts of the state depend on animals like walruses, polar bears and seals for their nutritional, cultural and economic well-being, according to the report. However, these wild game species also are a significant source of trichinellosis, which is caused by consuming raw or undercooked meat that is infected with the roundworm Trichinella.
According to Castrodale and colleagues, the first outbreak occurred among five members of one family who reported eating raw or pan-fried walrus cooked to a medium doneness around the date of July 17, 2016. The second outbreak occurred in May, less than 100 miles from the first outbreak in a community that uses the same hunting grounds in the Northern Bering Sea to harvest walruses.
The index case in the first outbreak was an adolescent girl who reported symptoms beginning around 1 month after eating the walrus meat, according to the report. Her symptoms included severe lower extremity edema and pain, difficulty walking, a pruritic rash, weakness, fever and myalgia. She was evaluated at a village health clinic on Aug. 15 and referred to an Anchorage hospital, where she was admitted on Sept. 8.
At the same time, the girl’s father and adolescent brother also were evaluated for trichinellosis. Eventually, the girl and her father were diagnosed with laboratory-confirmed trichinellosis, and her brother was diagnosed with probable trichinellosis. Weeks later, on Sept. 19, staff at Norton Sound Regional Hospital reported two more patients with trichinellosis — the girl’s aunt and uncle, who had eaten raw walrus meat sometime near the beginning of August. Both were diagnosed with laboratory-confirmed trichinellosis, although investigators could not determine if they had eaten meat from the same walrus. All five patients were treated with albendazole and two received prednisone.
The index patient in the second outbreak was an adult man who was transported to Norton Sound Regional Hospital with severe muscle and joint pain and diagnosed with probable trichinellosis, according to Castrodale and colleagues. Investigators identified four of the man’s neighbors, including his mother and adult sister, as having likely exposure to Trichinella through a shared meal.
Two patients — the man’s mother and sister — were diagnosed with confirmed trichinellosis, and the other two with probable trichinellosis. All five patients in the second outbreak were treated with albendazole, and the index patient also received prednisone.
According to Castrodale and colleagues, the meal had been prepared by the mother of the index patient, who said she boiled the walrus meat for 1 hour so that the exterior was fully cooked but the interior remained undercooked or raw — a preferred doneness, according to interviews with members of the community. Castrodale and colleagues tested walrus meat from household chest freezers and found one sample that tested positive for T. nativa, the arctic species of Trichinella.
Community warned
The second outbreak occurred just as the ADPH — prompted by the first outbreak — had begun a public service campaign about the risks of not fully cooking wild game. The campaign included fliers and a public service announcement that was read over local radio, according to Castrodale.
The flier, a copy of which was provided to Infectious Disease News by Castrodale, warns that the Trichinella parasite can survive freezing, smoking and drying, but can be killed by cooking meat to an internal temperature of 160°F. It lists common symptoms of trichinellosis — severe muscle aches and joint pain usually beginning 2 to 6 weeks after exposure — and advises patients to seek treatment and tell health care providers if they have eaten raw or undercooked meat.
According to the report, 227 of the 241 trichinellosis cases reported in Alaska since 1975 have been attributed to consuming meat other than pork, including species of bear, walrus and seal. Among these, 100 have been associated with eating walrus meat and another 24 with eating walrus or seal meat, according to Castrodale and colleagues. However, they note that only one case of walrus-associated trichinellosis was reported in the 23 years before the two outbreaks detailed in their report, a sharp decline from an incidence of 6.3 cases per year from 1975 to 1992.
“Reasons for this decline in incidence are unknown and might involve changes in parasite burden in walruses; the timing or location of walrus hunting; methods used to store, collect, handle, or prepare walrus meat for consumption; reporting practices among ill persons; and clinical testing methods or practices,” Castrodale and colleagues wrote.
On the heels of the MMWR report, the Alaska Department of Health and Social Services (ADHSS) released an epidemiology bulletin detailing the outbreaks and recommending that health care providers ask patients with suspected trichinellosis if they have eaten undercooked meat.
“These outbreaks underscore the importance of inquiring about consumption of commercially prepared and personally harvested meats, and about methods of meat preparation, when evaluating suspected trichinellosis cases, especially in areas where consumption of wild game in association with recreational or subsistence hunting is common,” Castrodale and colleagues wrote in their report. – by Gerard Gallagher
References:
ADHSS. State of Alaska Epidemiology bulletin: Outbreaks of trichinellosis linked to consumption of walrus meat. 2017. http://www.epi.alaska.gov/bulletins/docs/b2017_14.pdf. Accessed July 11, 2017.
Springer YP, et al. MMWR Morb Mortal Wkly Rep. 2017;doi:10.15585/mmwr.mm6626a3.
Disclosure: The researchers report no relevant financial disclosures.