Scientists Found Bear With Eye Worms That Can Infect Humans

A black bear in Pennsylvania died with parasitic worms attached to its eyes, and scientists suggest this is a disturbing find. A newly published research study says the Thelazia callipaeda eye worms are an “emerging zoonotic disease.” Zoonotic diseases can transfer from humans to non-human animals and vice-versa. Lovely.

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The study published in the Centers for Disease Control and Prevention (CDC)’s Emerging Infectious Diseases journal earlier this month. Researchers describe how someone legally harvested an adult female American black bear in November 2023 in Pennsylvania and noticed something funky on the bear’s eyes during the taxidermy-preparation process. Those funky things on its eyes were tiny worms.

Scientists took the worms for study and discovered nine female and four male adult T. callipaeda nematodes (aka eye worms). Interestingly, researchers say there were reports of two additional harvested bears from Pennsylvania with similar eye worm infestations. However, scientists didn’t get a chance to sample them.

Researchers say the presence of adult T. callipaeda eye worms in an American black bear suggests a transmission cycle in the United States. In the past decade, primary hosts of these eye worms were wild carnivores in Europe and Asia, not North America.

“American black bears are the most widely distributed species of bear in North America, inhabiting diverse regions throughout Mexico, Canada, and the United States,” researchers say. “Given the bears’ extensive geographic distribution and frequent and close interaction with humans and pets, thelaziosis in the black bear population raises concerns about the rapidly increasing incidence and geographic range of T. callipaeda eye worms in the United States.”

The study doesn’t discuss symptoms of the infection for bears or humans, but other reports suggest the eye worms can cause blindness.

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