Trichinella Outbreak from Eating Bear Meat and Cross-Contaminated Vegetables

By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

SYNOPSIS: A family outbreak of trichinellosis occurred after a feast of bear meat and vegetable kabobs that was caused by a species of Trichinella that is resistant to freezing.

SOURCE: Cash-Goldwasser S, Ortbahn D, Narayan M, et al. Outbreak of human trichinellosis — Arizona, Minnesota, and South Dakota, 2022. MMWR Morb Moral Wkly Rep 2024;73:456-459.

A 29-year-old man developed abdominal pain, diarrhea, myalgias, fever, and periorbital edema early in July 2022, which led to him repeatedly seeking care and to two hospitalizations. During the second admission, his white blood cell (WBC) count was 27,000/mL, with 27% eosinophils, and his serum creatine kinase was 1,040 units/L (reference range, 39 units/L to 208 units/L). At that time, a history of consumption of bear meat was obtained and, because of a suspicion of trichinellosis, he was treated with albendazole, and the case was reported to the Minnesota Department of Public Health. The detection of serum Trichinella immunoglobulin G (IgG) antibody confirmed the diagnosis.

An investigation determined that he had shared a meal with eight members of his extended family from Arizona, Minnesota, and South Dakota at a gathering in South Dakota. The meal included kabobs of meat from a black bear that had been harvested in May 2022 by one of the family members in northern Saskatchewan. The meat had been frozen for 45 days prior to its thawing and grilling together with vegetables. The meal was interrupted, and the meat was re-grilled because of a concern that it had not been adequately cooked.

Eight of the nine family participants subsequently were interviewed; all had eaten vegetables and five of them had eaten the bear meat. Symptoms consistent with trichinellosis were reported by six of the eight family members, including four who consumed both meat and vegetables and two who had eaten only vegetables. Three of the patients were hospitalized and were treated with albendazole. All six recovered from the illness.

Serum samples were obtained from six patients within four weeks of symptom onset, and two had detectable IgG anti-Trichinella antibody, and two of two were found to have Trichinella spp. deoxyribonucleic acid (DNA). Examination of samples of the bear meat that had been frozen in a household freezer for 110 days identified the presence of motile Trichinella larvae in a concentration of > 800 larvae per gram of tissue. Polymerase chain reaction (PCR) and whole genome sequencing identified the organism as Trichinella nativa.

COMMENTARY

Trichinellosis is a rare illness in the United States. The incidence was 0.1 per million population, with a median of 15 cases annually from 2008-2012 when cases were reported from 24 states and the District of Colombia.¹ One-fourth of cases were associated with ingestion of pork products, while bear meat was implicated in almost one-half. This incidence represented a marked decrease relative to previous years, occurring as a result of implementation of public health measures, including the 1980 Federal Swine Health Protection Act, which prohibited the feeding of potentially Trichinella-contaminated garbage to swine, together with recommendations regarding meat freezing and cooking at an internal temperature of ≥ 165°F (≥ 74°C) and prevention of cross-contamination of other foods, such as vegetables. Such cross-contamination accounted for the infection occurring in two individuals who had eaten only the vegetables. While freezing kills Trichinella spp. ordinarily implicated in outbreaks associated with pork, species such as T. nativa that predominate in Arctic and sub-Arctic regions (e.g., Saskatchewan) are freeze-resistant.

Three patients were no longer symptomatic at the time of their presumptive diagnosis and were not treated, while all three hospitalized patients were treated with albendazole. Treatment with this or mebendazole may have benefit during the early stage of infection, but its value during hematogenous larval invasion and especially after encystation is less sure.

I have seen patients with trichinellosis only once — and this was decades ago. It involved a family outbreak occurring after a feast of meat from a pig that they had purchased from a small farm. It was assumed the pig may have been fed garbage.

Reference

1. Wilson NO, Hall RL, Montgomery SP, Jones JL. Trichinellosis surveillance — United States, 2008-2012. MMWR Surveill Summ 2015;64:1-8.