Researchers have 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.
T. callipaeda is a nematode previously known for spreading in Asia and Eastern Europe, where it plagues carnivores, rabbits and hares, rodents, and primates (including humans). But it has recently undergone a swift and massive expansion in its range, including to Western Europe and North America. The initial 2020 detection in the US was in an eye of a pet dog in New York that had no travel history. Since then, it has shown up in at least 11 dogs — in New York, New Jersey, Connecticut, and Nevada — and two cats in New York, according to a study published in February. (The travel history of the Nevada dog is unknown, so it’s unclear where that infection occurred.)
In the new study, the UPenn researchers noted that the adult female bear with the T. callipaeda infection was “legally harvested” in Monroe County. The infection was detected as it was being processed for taxidermy. The researchers noted that two other bears harvested in the area had similar eye worm infections, but those cases were not investigated to determine the type of worms.
[…]
The worm spreads via a variegated fruit fly, Phortica variegate, that feasts on the tears and salty eye secretions of various mammals. There’s only limited data on P. variegate‘s distribution in the US. But it’s clearly an effective vector for the worm and efficient at delivering the parasite to new hosts.
The fruit fly’s role is not just to transport T. callipaeda, but also to help it grow. The life cycle of the worm starts in a host’s eye, where early-stage (L1) larvae are released by adult female worms and picked up by a male fly. The fly then becomes infected, with the larvae going through two developmental stages in the fly’s testes. When they’re ready, the third-stage (L3) larvae migrate to the fly’s mouthparts, where they can be transferred to a new host.
Nematodes are the stuff of nightmares. Fortunately, T. callipaeda is susceptible to ivermectin.