Researchers have identified more than a dozen parasitic worms within the eyes of a black bear, sparking concerns that these tiny creatures, which can lead to blindness, might pose a risk to humans.

The bear, found in rural Pennsylvania, was killed in November last year. The researchers isolated DNA from the tiny worms, measuring under 2 centimeters, linking them to Thelaziosis, a “new zoonotic disease,” as noted in their published findings.

Caroline Sobotyk, the study’s lead author and an assistant professor of clinical parasitology at the University of Pennsylvania, stated that this is the first instance of the parasite being documented in a wild U.S. animal.

While the worms have been detected in pets before, the discovery in a wild bear raises concerns about the potential spread of these eyeworms throughout the U.S.

“This heightens the possibility that humans, as well as our pets and other animals, could contract this parasite,” she explained.

The recent study published in the CDC’s Emerging Infectious Diseases journal cautions that the worms could be transmitted to both humans and domestic animals.

“Transmission wouldn’t be direct from wildlife to humans, but wildlife may serve as a reservoir,” said Kevin Niedringhaus, an assistant professor of wildlife pathology and co-author of the study.

The worms are carried by infected flies that can spread them to animals and possibly humans when the flies land near the eyes to feed on tears, according to the CDC. In severe cases, the worms can create ulcers on the eye’s surface, potentially resulting in blindness.

“The offspring of the worms are likely picked up by flies, which then transfer the parasites to another host, be it an animal or a person,” Niedringhaus added. The flies deposit eggs on the host’s face, which can lead to infection in the eyes.

Worms first seen in American pets in 2018

The extensive territories of black bears in the U.S. and their regular contact with humans and pets have scientists concerned about the potential spread of these worms. They also pose risks to endangered and threatened species, as noted by the researchers.

“The full effects of these worms on wildlife are still unknown,” Sobotyk mentioned.

The first identified case in the U.S. occurred when a Labrador retriever tested positive for the worms in 2018, with additional cases emerging in pets, particularly in the Northeastern region, over subsequent years. A study published in February reported instances of these worms in two cats and eleven dogs that had not traveled outside the U.S., leading researchers to conclude that “this parasite is on the rise in North America.”

“Both dogs and cats may contribute to keeping this parasite’s population sustained, and wildlife likely plays a part as well,” Niedringhaus explained.

The worms were initially recognized in Southeast Asia before their presence began to spread to Europe in the early 1990s, according to a report in the journal Trends in Parasitology. Niedringhaus mentioned that human cases have been documented in Asia.

Since then, cases have been reported throughout almost all European countries, with red foxes playing a significant role in their transmission, as indicated in the research.

Sobotyk reassured that severe or fatal outcomes from these worms are unlikely. They primarily affect the eyes and do not migrate to other body organs.

“No one will die from eyeworms,” she clarified.

“In the worst-case scenario, they could lead to blindness,” she continued. However, she noted that any infected individual would likely seek medical assistance before reaching such a critical point.

Niedringhaus advised pet owners to be vigilant about a new parasite by bringing their pets in for regular check-ups and watching for signs of illness, particularly unusual eye discharge.

“It’s crucial to keep a close watch on your pets primarily, as they are likely to be the carriers of possible transmission,” he noted.