Woman’s eye hosts more than a dozen cattle eyeworms | Science News for Students

Woman’s eye hosts more than a dozen cattle eyeworms

It’s the first known case of this parasite infecting a human
Apr 3, 2018 — 6:45 am EST
Fourteen of these cattle eyeworms were removed from the left eye of a young Oregon woman.

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.”

Power Words

(more about Power Words)

cattle     Also known as bovines (because they’re members of the subfamily known as Bovinae), these are breeds of livestock raised as a source of milk and meat. Although the adult females are known as cows and the males as bulls, many people refer to them all, generally, as cows.

Centers for Disease Control and Prevention (CDC)     An agency of the U.S. Department of Health and Human Services. CDC is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. It does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

hygiene     Behaviors and practices that help to maintain health.

infect     To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ or parasite to an individual.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject.

larva     (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)

nematode     A type of roundworm, usually found in soil, that also can live within other creatures as a parasite. It is usually quite small, with no eyes, ears or nose. However, the occasional species can grow up to a meter long.

parasite     An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

parasitology      A branch of biology that focuses on parasites and their hosts. Scientists who work in this field are known as parasitologists.

secretion    A liquid substance — perhaps a hormone, an oil or saliva — released by the body, often by an organ, such as the eye, pancreas or skin.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.


Journal:​ ​​ R. Bradbury et al. Case report: Conjunctival infestation with Thelazia gulosa: a novel agent of human thelaziasis in the United States. The American Journal of Tropical Medicine and Hygiene. Published online February 12, 2018. doi: 10.4269/ajtmh/17-0870.