Family Stricken With Brain-Invading Roundworms After Eating Undercooked Wild Game

Several family members from three states became ill with trichinosis — a disease caused by the roundworm Trichinella — after eating a meal of undercooked bear meat at a gathering in South Dakota.

According to a Centers for Disease Control and Prevention (CDC) report published on May 23, several people from Arizona, Minnesota, and South Dakota contracted Trichinella — a roundworm known to invade muscle and brain tissue — after sharing a bear meat dinner in 2022.

In July 2022, the Minnesota Department of Health received notification that a 29-year-old man was hospitalized due to symptoms including fever, severe muscle pain, and swelling around the eyes. Hospital officials suspected the individual was experiencing a case of trichinosis, an illness caused by Trichinella.

Upon investigation, health authorities discovered that six days before experiencing symptoms, the man attended a family dinner in South Dakota with several people.

The meal included black bear meat, which one family member acquired on a hunt in northern Saskatchewan, Canada, in May 2022. The hunting outfitter told the family member to freeze the meat to kill potential parasites.

A total of nine individuals attended the dinner. Of those, the 29-year-old man and six others became infected with Trichinella. Three of the six were hospitalized and recovered after doctors treated them with an anti-parasitic drug. The remaining family members recovered without the need for treatment.

When officials tested the bear meat, which had been frozen for a total of 110 days, the results were positive for Trichinella nativa, a freeze-resistant roundworm species.

Preventing illness from brain and muscle-invading roundworms

Trichinosis is extremely rare, and people typically acquire Trichinella from consuming raw or undercooked wild game meat or domestic pork. After ingested, the roundworm larvae invade the intestines and grow into adult worms. Then, they can travel to muscles, causing symptoms including fever, headache, muscle pain, and eye swelling.

Trichinella can also enter the heart, lungs, or brain, causing severe illness.

According to the CDC, at least 1% to 24% of black bears in Canada and Alaska have Trichinella, with higher rates among carnivores such as polar bears or wolverines.

Strategies to prevent trichinosis include cooking wild game to a temperature of at least 165ºF and pork to at least 160ºF. While freezing meat may kill the larvae in pork, it is not a reliable way to eliminate the brain/muscle-invading roundworm in wild game.

Moreover, drying, smoking, salting, or microwaving does not kill Trichinella.

Meat handling is also critical. To avoid ingesting Trichinella, a person should keep raw meat and its juices away from other foods and thoroughly clean equipment, surfaces, or hands that have come into contact with raw meat.

Though rare, the CDC says that from January 2016 to December 2022, seven trichinosis outbreaks occurred in the United States, including 35 probable and confirmed cases. In most of these cases, bear meat was the suspected or confirmed source of infection.