A parasitic outbreak that left at least 10 people with facial swelling last year was caused by undercooked bear meat served at a mountain affair in North Carolina, according to a new report from the Center for Disease Control.

The undercooked meat infected 10 of the 22 attendees of the November 2023 affair, who reported consuming the bear with Trichinellosis, more commonly referred to as brain worms.

It is a rare parasitic disease known to cause a fever, severe muscle aches, and swelling around the eyes.

"Although Trichinella infections remain rare, thousands of bears are harvested each year in North Carolina," the CDC.

"An increasing percentage of recent cases are associated with consumption of wild game meat."

Meat tainted with roundworm larvae, which are commonly found in carnivorous and omnivorous animals, cause Trichinellosis, according to the CDC.

The larvae "invade the small bowel mucosa and develop into adult worms."

The brain worms used to be more common in the United States, but saw a sharp decline after pig-raising practices were refined throughout the late 20th century, according to the Department of Agriculture.

Eight of the 10 people who reported falling ill went to hospitals for symptoms that included "headache, swelling of eyes and face, nausea, and/or diarrhea," officials said.

The mountain trip was staged in November in Swain County, with all those who contracted Trichinellosis living in Swain, Cherokee and Graham counties, the North Carolina Division of Public Health reported.

The infected ranged from 10 to 40 years old.

In May 2024, six people attending a family reunion contracted Trichinellosis after eating undercooked bear kabobs.

The same happened in Canada in 2022 when another six cases were identified -- except only four members of the party consumed the bear meat.

Two of the patients only ate vegetables that day, but it had been cross-contaminated by the meat, according to the CDC report.