Woman’s eye hosts more than a dozen cattle eyeworms

It’s the first known case of this parasite infecting a human

Fourteen of these cattle eyeworms were removed from the left eye of a young Oregon woman.

CDC

A 26-year-old woman from Oregon felt something bothering her left eye. And a week later, she pulled out of that eye a nearly see-through worm. The creature was nearly 1-centimeter (0.4-inch) long. The species was a type of cattle eyeworm. This was the first known case of one being found in a human.

This small, parasitic worm — Thelazia gulosa — is a type of nematode. It can be found in North America, Europe, Australia and central Asia. As its name suggests, it normally infects the large eyes of cattle. Before it gets there, the worm spends its larval stage in the stomach of the aptly named face fly (Musca autumnalis). As the fly feasts on cattle tears and other eye secretions, it spreads the nematode larvae. The animal’s eye then becomes their home until they become adult worms.

Though rarely, two other Thelazia species are known to infect humans. One of them has infected more than 160 people in Europe and Asia. Another — a species found in dogs — was behind 10 cases in North America. The new eyeworm was not expected to be found in people.  

Richard Bradbury works at the U.S. Centers for Disease Control and Prevention in Atlanta, Ga. As a medical parasitologist, he studies parasites and their hosts. He finds the Oregon case to be “very rare event and exciting.” Though, he concedes, it’s “perhaps not so exciting if you are the patient.”

Over a period of 20 days, the woman and her doctors removed 14 worms from her eye. After that, her eye caused her no more discomfort. Bradbury and his colleagues described the new case February 12 in the American Journal of Tropical Medicine and Hygiene.

The young woman had been horseback riding near cattle farms in Gold Beach, Ore. This may explain where she came face-to-face with the fly.

“It is just unfortunate for the patient,” Bradbury says, “that she was not able to swish away that one infected fly quickly enough from her eye.”

Aimee Cunningham is the biomedical writer at Science News. She has a master’s degree in science journalism from New York University.

More Stories from Science News for Students on Health & Medicine