Family members in U.S. infected with muscle worms after eating undercooked Sask. bear meat

Many people who shared a meal of bear meat, harvested from northern Saskatchewan, at a family gathering in South Dakota were infected with trichinellosis, according to a new report from the U.S. Centers for Disease Control and Prevention.

Experts say the parasite that causes the disease is common in wild meat.

In July 2022, the Minnesota Department of Health was notified that a man, 29, had been hospitalized multiple times over a two-and-a-half-week period with symptoms including fever, severe muscle soreness and swelling around the eyes.

Following his second hospitalization, the man revealed to doctors that he and “eight extended family members from three states” (Arizona, Minnesota and South Dakota) had attended a family gathering where they shared kabobs of black bear meat that “had been harvested by one of the family members in northern Saskatchewan.”

What went wrong?

Trichinellosis is a parasitic zoonotic disease transmitted through the consumption of meat from animals infected with trichinella nematodes.

“It’s unfortunate but unsurprising,” said Douglas Clark, an associate professor in the school of environment and sustainability at the University of Saskatchewan. 

Clark said there have been trichinellosis outbreaks in people from eating undercooked bear meat, wild boar and even walrus.

He said that in this case, things became difficult for the family because the meat was inadvertently served rare.

After some of the family members began eating the meat and noticed it was undercooked, the report says, the meat was recooked before being served again. 

“Bear meat is often dark purple in colour, so if you’re not used to cooking bear meat, it can be hard to judge when it’s done or not done,” Clark said.

The report says the meat had been kept in a household freezer for 45 days until being thawed and grilled with vegetables. 

While some parasites are killed by freezing, Clark says, many common species of trichinella found in Canada can survive it.

“They can only be killed by cooking the meat to a high temperature,” he said, noting an internal temperature of at least 74°C is necessary to kill the parasites.

However, members who did not consume the meat and only the vegetables that had been cooked with the meat also had symptoms consistent with trichinellosis.

Clark says that’s because trichinella-infected meat can cross-contaminate other foods with contact.

CBC asked Saskatchewan’s Ministry of Health about recent cases of human trichinellosis in the province. The ministry responded with a statement.

“Human trichinellosis cases are rare and usually acquired through consumption of wild game meat, including bear, infected with trichinella worms,” the statement said.

“In addition to the outbreak described in the recent CDC report, the Saskatchewan Ministry of Health is aware of a small cluster of Saskatchewan residents who were exposed to the Trichinella pathogen in 2019. In this incident, the exposure was associated with consumption of meat harvested outside of Saskatchewan.”

How severe and widespread is trichinellosis?

Emily Jenkins, a professor of veterinary microbiology who has done extensive research on zoonotic parasites including trichinella, said the disease “pops up every couple years associated with bear meat” and as recently as 2021.

She says it often comes up with tourists because Indigenous people who harvest wild animals are aware the meat must  be well cooked.

“It’s often tourists, hunters coming from away who will take a souvenir home with them … so it’s fairly common that people who don’t have that protective knowledge are the ones who unfortunately become infected and that they’ve also shared the meat widely because it’s a delicacy, a gourmet thing,” Jenkins said.

“We’ve had massive outbreaks in France, for example, associated with bear meat from Canada, just because people didn’t necessarily have that protective knowledge.”

Saskatchewan has also seen some recent cases of the disease. In 2000, there was an outbreak of trichinellosis in two northern Saskatchewan communities due to consumption of bear meat.

Originally, the parasites were associated with pigs, Jenkins says. In wildlife, she says, usually the more carnivorous an animal is, the more likely humans can get trichinellosis from eating it.

“Polar bears, wolverines that are really top level predators and scavengers, 80 to 90 per cent of them can be infected,  grizzly bears a little bit less, roughly 50 to 60 per cent. And then our black bears could be even less than 30 per cent of them.”

Jenkins says her team has now discovered the thirteenth species of the parasite.

“This new species called T13, we named it trichinella chanchalensis after the place in the Yukon where we found it,” she said.

How does this spread?

Jenkins says the muscle-dwelling roundworm only transmits between carnivores. 

“It loves muscle and often ends up in skeletal muscle like arms and legs. But where it really shows severe problems is if it gets in the heart — it can cause cardiac disease,” she said.

Another common symptom, Jenkins says, is swelling of the facial muscles because the larvae move through the body and end up in a variety of places, including the eye or the brain.

Parasitic worms made international news earlier this month when U.S. presidential hopeful Robert F. Kennedy Jr. disclosed that a parasitic worm he contracted years ago “ate a portion” of his brain,” causing potential cognitive issues.

Jenkins says most people are lucky enough to get away with just an upset gastrointestinal tract about a week or so after they eat it.

“But then a month or so later, they’ll start getting muscle aches and feel like they have a full body flu, but it’s related to those larvae getting into their muscles,” she said.

She said the parasite is usually consumed as a larva in meat, and it develops to its adult stage in the intestine. Those adult worms reproduce, make their own larvae and they migrate to muscles.

“They’re pretty impervious,” she said. “It’s very hard for drugs to access those larvae. By the time it’s out in your muscles, all we can do is give an anti-parasite drug and manage the inflammation.” 

Once they get into the muscles they deactivate and form a protective cyst, allowing them to live for years.

“It’s treatable, especially if you could treat it in that initial week phase,” she said. “But once you’re infected, probably you’re infected for years if not for life.”