The Unseen Threat: How Parasitic Eyeworms are Expanding Their Territory in the U.S.

The Silent Spread: Eyeworms Find New Hosts

And now they can say, with a shuddering surprise, that our cousins – American black bears – are now among its hosts. The study, published in the journal Emerging Infectious Diseases, documents how parasitic eyeworm has spread to the US, most likely via the eyes of birds that migrate from Europe and Asia. The infections have been documented in moose, deer, elk and mountain goats. A black bear found dead in Pennsylvania with worms in its eye socket and around its brain was the first known case of Thelia callipaeda infection in the American bear. Aggressive rounds of worm reproduction are likely to follow – and not necessarily just in the wild. Though new to North America, T callipaeda is more familiar elsewhere. It’s very similar to the parasitic worm that causes human eye worm infection, T sinclairi, which can typically be cured with a four-week course of mebendazole, the same drug used for roundworms in small children. And a different species of eye worm, T gulosa, thrives in dogs, who spread it to other canines and occasionally humans. In 1955, researchers in Texas reported the first 12 cases of human eye worm infection in the US.

Thelazia Eyeworms: A Closer Look

Thelazia eyeworms depend for their transmission on fly species that look much like the common house fly, but that prefer to dine on fluid secretions from the body, especially tears. The worms get themselves attached to the flies during their meal and, as they mature inside the insect, are carried to new hosts. It’s a fascinating and bewildering life cycle, made more alarming by the fact that the hosts include humans, pets and now, wildlife.

Swift Spread Across Continents

Originating in Europe and Asia, T callipaeda recently emerged in the US, with its first documented local case in 2018 in a New York dog. Since then, reported infections – in dogs and cats in the Northeast – have surged. The latest case, this time in an American black bear, marks the pox virus’s jump from pets to wildlife and increasing spread across geographic territory.

The Bear Necessities: Understanding the Impact

Because of the widespread distribution of black bears, which harbour T callipaeda, and because those bears frequent humans and pets, the risk of spillover can grow rapidly, emphasising the need for greater study and public awareness.

Beyond Bears: A Growing Concern for All

Its broad host range in the U.S., which includes some threatened species, points to the possibility that T callipaeda might be a threat beyond the wild and domesticated bear populations. Now that there are documented human cases of T gulosa, another haemal eyeworm species, vigilance and continued study of its life cycle, transmission and prevention are of the essence.

A Swift Response: Containment and Prevention

When it came to identifying these Toxoplasma callipaeda, there was no better teacher than Los Angeles The next step in containing and preventing the spread of T. callipaeda lies in better understanding the mechanisms of transmission and the parasite’s lifecycle – including exactly how wildlife is becoming infected with the parasite when it is often actively avoiding its main host, the cat. Reducing the incidence of infections relies critically on identifying any known risk factors for transmission, and communicating this information to the general public, especially those who own pets and come into daily contact with wildlife.

Understanding Swift: The Invader

Worms in your eyes? Sound like science fiction? In the US, eyeworms like T callipaeda are a frighteningly real threat. We must remain vigilant and do our best to control these parasites before they erupt into a major human health crisis. Educate yourself and take care. Check your eyes.

Aug 16, 2024
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