Invasive Parasitic Eyeworm Could Use Bears to Spread Across Iowa, Illinois, & Wisconsin

A recent discovery of parasitic worms in a black bear in Pennsylvania has sparked concerns about the potential spread of this emerging disease in the Midwest, including Iowa, Illinois, and Wisconsin where bear populations have increased, and more sightings have been reported. The parasitic worm Thelazia callipaeda, or eyeworm, is an invasive species that has been increasingly detected in various parts of the United States, especially in domestic pets and now, for the first time, in wild animals.

What is Thelazia callipaeda?

Thelazia callipaeda is a type of parasitic worm that typically infects the eyes of its hosts. It is primarily transmitted by flies that feed on the tears of animals. When an infected fly lands near an animal's eye, it can deposit the larvae of the worm, which then develop into adult worms within the eye. The worms can cause a range of symptoms, like: mild irritation, excessive tearing, ulcers on the eye's surface, and blindness in extreme cases. The video below is not for the faint of heart or those with a queasy stomach. You've been warned!

Although originally found in parts of Asia and later Europe, Thelazia callipaeda has now made its way to the U.S., with cases being reported in states like New York and New Jersey. More concerning for Tri-State residents is the possibility that these worms will begin spreading to our local wildlife.

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The presence of black bears in Iowa has been confirmed by the Iowa Department of Natural Resources (DNR), with sightings on the rise in Illinois as well. Wisconsin has an extremely healthy black bear population, particularly in areas close to their borders with Iowa. Based on the new findings, these states could see an increase in the presence of the eyeworm, as black bears often come into contact with human-inhabited areas. This may cause them to act as potential reservoirs for the parasite. This interaction increases the chances of transmission to domestic animals like dogs & cats, and, potentially, humans.

For residents of the Tri-States, the emergence of Thelazia callipaeda is a reminder of the importance of vigilance, especially for pet owners. The parasite poses a risk not only to wildlife but also to domestic animals and, by extension, humans. Pets are particularly at risk, as they are often outdoors and can easily come into contact with the flies that transmit the worm.

Regular veterinary check-ups are essential to catch any signs of infection early. Symptoms in pets may include excessive tearing, redness around the eyes, or signs of discomfort. Early detection and treatment can prevent more serious complications, such as blindness.

The fact that Thelazia callipaeda has been found in wild animals like black bears, which are common across parts of Iowa, Illinois, and Wisconsin, means that the parasite could spread further across these states. While the risk to human health remains relatively low at this stage, the possibility of infection is present, particularly in areas where wildlife and domestic animals frequently interact or co-mingle.

As this parasitic disease continues to emerge in new areas, it’s important for communities in the Midwest to stay informed and take appropriate precautions to protect both their pets and themselves from the potential impacts of this nasty eyeworm.