Parasitic worms likely entered eye of woman during Carmel Valley trail run 'Humans are suitable hosts'

A 68-year-old trail runner may have been infected by parasitic eye worms during a jog last year in Monterey County's Carmel Valley. The roundworm has only been found in humans once before. A 68-year-old trail runner may have been infected by parasitic eye worms during a jog last year in Monterey County's Carmel Valley. The roundworm has only been found in humans once before. Photo: Yoh4nn/Getty Images/iStockphoto Photo: Yoh4nn/Getty Images/iStockphoto Image 1 of / 25 Caption Close Parasitic worms likely entered eye of woman during Carmel Valley trail run 1 / 25 Back to Gallery

Parasitic eye worms may have crawled into the eye of a trail runner while she was jogging in Monterey County's Carmel Valley.

The runner, a 68-year-old woman from Nebraska who spends her winters in the area, became only the second person known to have been infected by Thelazia gulosa, a roundworm that is carried by flies, according to a case study published recently in the journal Clinical Infectious Diseases. The worm, also known as a nematode, is normally found in cattle.

Researchers say the eye worm could be an emerging zoonotic disease in the United States. A zoonotic disease is one that jumps from animals to people.

The woman told doctors she recalled a specific run in the area in February 2018 in which she ran into a swarm of flies. She was "swatting the flies from her face and spitting them out of her mouth," according to the study. That could have been the moment of infection.

In March 2018, she felt an irritation in her right eye. When she flushed it with tap water, a half-inch-long roundworm popped out. She took a closer look and saw a second worm, which she also plucked. A trip to a Monterey eye doctor the next day resulted in the discovery of a third worm.

That nematode was sent to the Centers for Disease Control and Prevention, whose scientists determined that it was T.gulosa. The roundworm hitches rides on certain kinds of flies that drink cow eye secretions, allowing the parasite to enter the bovines' eyes.

The CDC researchers noted that the worm they examined was developing eggs, "indicating that humans are suitable hosts for the reproduction of T. gulosa," according to the Clinical Infectious Diseases study.

A fourth worm turned up when the woman returned to Nebraska. After daily eye irrigation for two weeks, no further worms were found.

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The first human infected by T.gulosa on record was a 26-year-old Oregon woman in 2016.

The parasite has been known to infect North American cattle since the 1940s. But because the two human cases are only two years apart, scientists think it could be a new health threat to people as well.

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Mike Moffitt is an SFGATE Digital Reporter. Email: moffitt@sfgate.com. Twitter: @Mike_at_SFGate