A 68-year-old US woman has earned a very unwanted distinction: She is just the second human on record to show up at the doctor's office with parasitic eye worms more common to cows, reports Live Science. The unidentified woman splits her time between Nebraska and California, and researchers explain in Clinical Infectious Diseases that it appears she picked up the parasite in the latter state's Carmel Valley. Exactly how is unclear, but the woman is a trail runner and she recalls running through a swarm of flies one day in February 2018—so many flies that she ended up spitting some out of her mouth. The next month, she felt an irritation in her right eye, and when she flushed it with tap water, a half-inch roundworm came out. She removed a second worm herself, then went to an eye doctor, who removed a third.
The worms were identified as a species known as Thelazia gulosa, which have shown up in only one other person—a 26-year-old Oregon woman in 2016. The parasites have been known to show up in cattle, and National Geographic notes that they're spread by flies buzzing around cows' heads. That gibes with the trail runner's recollection of running through a swarm. The discovery of a second case in three years suggests the parasites are becoming more common, and researchers suggested closer monitoring of the ailment in cows to get a better handle on things. The trail runner, for the record, removed a fourth worm on her own, and now appears to be worm-free. However, one of the worms in her eye had developing eggs, suggesting that humans "are suitable hosts," note the researchers. (The Oregon woman had 14 worms.)