When Abby Beckley began to feel some discomfort in her left eye, she thought it was just a harmless irritation caused by a stray eyelash.
However, it persisted for a week despite several remedies. One day, after flushing her inflamed eye with water, the 28-year-old from Grant Pass, Oregon examined it in the mirror and spotted something frizzy.
She pulled it out, only to discover something unexpected and terrifying. It was actually a translucent worm as thin as a thread, measuring almost an inch long.
"It was moving," narrates Beckley. "And it then it died within about five seconds."
For three weeks in August 2016, 14 of these parasites were extracted, saving her from edema, conjunctivitis, or potential blindness.
This is already the 11th case of eye worm infection to be reported in North America but it made history for being the first to result from a new species that has never affected humans.
Thelazia: What Are Parasitic Eye Worms?
Thelazia or eye worms are primarily found in cats, dogs, pigs, cattle, and horses. They start out as sheathed larvae then later grow into adults capable of reproduction.
Transmission is facilitated by female flies of the Musca and Fannia subgroups, which are known to feed on protein-rich eye secretion of animals.
These insects carry and deposit the parasite's larvae into eyeballs of other animals where they can thrive for up to 30 months while causing loss of vision. For treatment, veterinarians often use ivermectin.
In cases involving human hosts, the most common symptoms are inflammation and the uncomfortable sensation that a foreign particle is stuck inside the eyeball. While medication is not needed for treatment of infected patients, the worms would have to be manually extracted using forceps similar to a tweezer.
Thelazia Californiensis Vs. Thelazia Gulosa
In a study published Feb. 12 in The American Journal of Tropical Medicine and Hygiene, researchers with the CDC reported that Beckley's infection came from face flies present in a local coastal area with a number of cattle farms.
Several eye worms from the Oregon case were sent to the federal agency's parasitic disease laboratory where they were identified as cattle eye worms or Thelazia gulosa.
The research team initially thought the samples belong under the Thelazia californiensis species because it is the only type that has caused human infection in the U.S. but they were wrong. The extracted parasites had a different anatomy.
"We had to go back to papers published in German back in 1928 to help identify this worm as Thelazia gulosa," says the study's lead author, Richard Bradbury of the CDC's Division of Parasitic Diseases and Malaria.
Previously, it was assumed that there are only two species of eye worms capable of infecting humans: the Thelazia californiensis and Thelazia callipaeda. This figure has now been bumped up to three with the addition of Thelazia gulosa.
All cattle worms were successfully removed from Beckley's eye. Her vision is now back to normal.