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Washington, February 13
A US woman has become the world’s first known person to get an eye infestation of a worm known to only affect cattle, say doctors who extracted 14 worms — each measuring up to half an inch long — from the eyes of the patient.
Scientists reported the case of the first known instance of a human infection with Thelazia gulosa, a type of eye worm found throughout the northern US and southern Canada. These eye worms are spread by flies that feed on tears.
“Cases of eye worm parasitic infections are rare in the USA, and this case turned out to be a species of the Thelazia that had never been reported in humans,” said Richard Bradbury, from the US Centers for Disease Control and Prevention (CDC) Division of Parasitic Diseases and Malaria.
“Previously, it was thought that there were only two different species of these (Thelazia) eye worms that infected humans worldwide. Now, we have to add Thelazia gulosa, a third one to the list,” said Bradbury, lead author of the study published in the American Journal of Tropical Medicine and Hygiene.
The infection in the Oregon woman presented as a typical eye worm infestation. The woman first reported sensing an irritant in her left eye.
About a week later, she removed a small, translucent worm.
According to the study, a total of 14 worms – all less than half an inch long – were extracted from the woman’s conjunctiva and the surface of her eye over a two-week period before her symptoms ceased.
Physicians focused treatment on removing the eye worms with small, tweezer-like forceps or irrigation of the infected eye.
In Asia and Europe, a subcutaneous dose of the anti-parasitic drug ivermectin has been used to cure human infections.
Eye worms, known as Thelazia, are found in a variety of animals – including cats, dogs, and wild carnivores like foxes. They are transmitted by different types of flies.
Most of the time, people who get these eye worms experience inflammation and the sensation that there is some type of foreign body in the eye, said Bradbury.
Symptoms typically resolve after the worms are removed, he said.
Occasionally, the worms will migrate across the surface of the eye and cause scarring of the cornea and even blindness.
Human infections with eye worms are most often seen in the elderly or in young children, given that both patient groups “may be less able to keep flies away from their faces.
The researchers suspect the woman encountered face flies, which also feed on eye secretions, while horseback riding and fishing in a coastal area of Oregon where cattle farming is common.
Several of the worms from the Oregon case were sent to the CDC’s parasitic disease reference laboratory, where examination identified them as cattle eye worms, which are spread by a type of fly known as face flies.
Meanwhile, another species of the Thelazia eye worm previously known to infect humans, Thelazia callipaeda, originating from Asia, has spread across Europe, where it is transmitted by a common fruit fly, Phortica variegata.
