Yes, you read that title right. Worms in people's eyes. The Centers for Disease Control and Prevention (CDC) has identified them as Thelazia gulosa, a parasitic roundworm that typically grows between the outer membrane of the eyeball and the eyelid of a cow's eye. These worms are incredibly small, no bigger that the very tip of your finger. They stick to the eyes of cattle or other animals (like outdoor pets) to grow and reproduce. Humans have been safe from them... until recently.
In October, a second patient reported an infection of T. gulosa eyeworms in 2018, after encountering a swarm of flies while running on a trail. The report comes a mere year after the first patient to report an infection of eyeworms in 2017. With these two rare incidents happening within a year of each other, scientists are now concerned that this could be a sign of an "emerging zoonotic disease" — a type of infection that transfers from animals to humans.
T. gulosa may be a tiny worm, but it has its own, parasitic ways of jumping to hosts. This is how it works according to the CDC: Worm larvae are ingested by face flies, where they stay and grow to an "infective stage" within the fly. When the flies go to feed on the eye secretions of a cow, such as tears, the grown larvae exit the bug and enter the conjuctival sac — the space between the eyeball and eyelid — of the new host. There, they find mates and have plenty of baby worms to spread within the host's eye secretions. When the face flies come back to feast on more liquid, they ingest the worm larvae and become hosts to the larvae until they reach their infective stage. Then, the parasitic cycle continues all over again.
The two patients who were infected found numerous worms within their eyes when they came into contact with flies. The first patient suspects she was infected while passing through cow pastures. Over the span of 20 days, she had 14 wiggling worms in total pulled from her eye. Most were dead, noted the specialist treating her, because they didn't have another face fly to spread to.
The second patient was infected while running on a trail. She encountered a swarm of flies during her exercise, but thought nothing of it until her eye became irritated a month later. She flushed out her first worm — nearly half an inch long! — with tap water, then later removed others as she found them. Thankfully, she only had to deal with four worms.
The surprising discovery about the second patient's worms? One of them was a female, filled with eggs that were developing larvae. This became proof that human eyes were perfectly suitable environments for a male and female worm to mate and reproduce. The finding, and the incidents, are significant discoveries. But why are the worms only now infecting humans? Scientists still have yet to find the answer to that question. There's a possibility that these occurrences indicate that there might be so many animals infected with these parasites that it's spilling over onto human hosts. However, researchers say they can't tell for certain without anyone looking into the infection rate among animals.
The chances of this happening to other people remains rare, but scientists recommend going to the doctor if your eye is irritated or it feels like something is wiggling in your eye. Especially if you've been near cattle or had a bunch of flies in your face. The sooner the doctors can remove the worms, the less likely there will be any long term trauma to the eye. Physical trauma, that is. There's no accounting for the mental trauma of having a colony of worms in your eye, ughghghgh.