(CN) – An Oregon woman is the first known human to be infected with a kind of eye worm thought to only exist in cattle, leading scientists to speculate that Americans may be vulnerable to the parasite.
A study published today in the American Journal of Tropical Medicine and Hygiene indicates humans may be more at risk for Thelazia worms, a group of small parasitic nematodes found in a number of animals.
Of the different types of Thelazia worms, scientists previously believed only two species infected humans.
But a recent report from the U.S. Centers for Disease Control and Prevention found a woman’s eye was infected with Thelazia gulosa, which is spread by flies that feed on the liquid in the eyeballs of cattle.
That worm is found throughout the northern U.S. and southern Canada, but until now was never found to affect humans.
The woman, who lives in Oregon, reported irritation in her left eye and removed a worm that was less than half an inch long from it a week later. Over the course of two weeks, more than a dozen worms were extracted from her eye, according to the study.
She may have been infected while horseback riding and fishing near the Oregon coast, where there are cows and flies that feed on their eye secretions.
The researchers say people affected by eye worms typically experience a sensation like there is a foreign object in their eye, and the eye becomes inflamed. Though symptoms usually resolve when the worms are removed, they can also move across the eye, causing cornea damage and blindness.
The CDC examined some of the worms, and identified them as cattle eye worms which are spread by a kind of fly called “face flies.”
Richard Bradbury, the lead author of the study, said the researchers had to refer to German studies from the 1920s to help identify the worm.
“Previously, it was thought that there were only two different species of these (Thelazia) eye worms that infected humans worldwide,” Bradbury said. “Now, we have to add Thelazia gulosa, a third one to the list.”
In 2016, researchers revealed a man in Croatia was the first person in that country to be infected by the Thelazia callipaeda worm.
The callipaeda worm, also known as the “oriental eye worm” is found in a species of fruit fly. It has spread across Europe, but has not been found in North America.
Last year, a British research team reported several cases of dogs in the United Kingdom that had been infected by the worm. In one case, the dog had been imported from Romania, and in two other cases the dogs had traveled to Italy and France.
And Italian veterinary scientists showed that fruit flies in upstate New York are capable of carrying the callipaeda worm.
“We’re not sure of the exact distribution of these fruit flies in North America,” said lead author Domenico Otranto.
“But their presence in upstate New York suggests this geographic area is potentially suitable for spreading the eye worms that cause human infections in Europe and Asia.”