The U.S. Centers for Disease Control and Prevention (CDC) says the eye parasites, which can potentially infect humans, have been previously identified in dogs and cats in the United States. The most recent infection was discovered in a black bear in Pennsylvania.
On August 14, the CDC released an Emerging Infectious Diseases report detailing a case of Thelaziosis, an emerging zoonotic disease caused by nematodes of the genus Thelazia, in a black bear killed in Pennsylvania in 2023.
Thelazia callipaeda eyeworm was first detected in one dog in New York in 2020. Since then, 11 dogs and two cats in the U.S. have contracted the parasite.
The worm is transported by the variegated fruit fly and spreads to the eyes when the fly feeds on the tears and eye secretions of mammals. Common symptoms of the eye worm infection include eye redness and excessive tearing, but corneal ulcers and blindness can also occur.
In countries where Thelazia callipaeda is more common, such as Asia and Eastern Europe, it's known to infect a wide range of mammals and even humans.
Treating the infection involves physically removing the adult worms from the eye and deworming medications like ivermectin.
The CDC says that the prevalence of this eye worm species has increased worldwide over the past decade. This latest report shows that the parasite is potentially expanding in the U.S. via black bears, which inhabit diverse regions throughout the country.
"The presence of the zoonotic nematode in such a wide range of hosts implicates exposure and risk for transmission to threatened and endangered species and direct or indirect risk for transmission to humans and domestic animals," CDC researchers wrote.
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