Enlarge / An adult Thelazia callipaeda in the eye of a cat.

In a battle of bear versus exotic eye worm, the eye worm wins—and that's bad news for all of us.

Researchers on Wednesday reported the first known infection of an exotic eye worm in a black bear in the US, which was killed in Pennsylvania in November 2023. The bear had at least 13 adult parasitic worms pulled from its eyes, and the researchers identified them as the invasive, potentially blinding species Thelazia callipaeda, which was only first detected in the US in 2020.

The bear's infection shows that the worm is rapidly expanding both its range of potential hosts as well as its geographic foothold in the US. In all, the finding "implicates exposure and risk for transmission to threatened and endangered species and direct or indirect risk for transmission to humans and domestic animals," write the researchers, led by veterinary experts at the University of Pennsylvania. Their report appears today in the journal Emerging Infectious Diseases.