Abstract
Background
In July 2022, the Minnesota Department of Health was notified of a patient with fevers, myalgias, periorbital edema, and eosinophilia; providers suspected trichinellosis. Human trichinellosis is rare in the United States and usually acquired from wild game meat. We investigated to confirm the diagnosis, ascertain additional cases, and identify the source of infection.
Methods
Trichinellosis was defined as compatible symptoms in a person who consumed an epidemiologically implicated meal (probable) or had Trichinella antibodies (confirmed). Blood samples from exposed persons were tested for Trichinella antibodies and with unbiased sequencing for microbial cell-free DNA. Microscopy and a parasite detection assay based on deep sequencing were performed on suspected source meat.
Results
One week before symptom onset, the patient and 8 relatives from 3 states shared a meal including meat from a bear harvested in Saskatchewan, Canada. The meat was frozen for 5 weeks until being grilled with vegetables and served rare. There were a total of 6 cases (4 probable and 2 confirmed, attack rate = 75%). Six persons had a trichinellosis-compatible illness, of whom five submitted samples for Trichinella antibody testing and two had positive results. Plasma samples from the two antibody-positive patients were tested for microbial cell-free DNA, and both were positive for Trichinella spp. DNA. Motile Trichinella species larvae ( >800 larvae per gram) were identified in bear meat frozen for 4 months. Deep sequencing detected 3 Trichinella genotypes, 2 of which matched reference sequences for T. nativa and Trichinella T6. The third genotype did not match any reference sequence; the closest match (94%) was Trichinella T9, which has only been detected in Japan.
Conclusion
We used multimodal diagnostic testing to characterize an outbreak of human trichinellosis and confirm bear meat as the source. Freezing kills Trichinella species commonly implicated in pork-associated outbreaks, but T. nativa and Trichinella T6 are freeze-resistant. Consumers of wild game meat should be informed that adequate cooking is required to kill Trichinella parasites. Further work on identification and classification of Trichinella species in North America is needed.
Disclosures
David Berman, DO, Precision Health Solutions, St. Petersburg, Florida: Advisor/Consultant