Eyeworms in Cats

Eyeworms (Thelazia californiensis) are more of an issue along the Pacific Coast of the United States, especially in California. They have been found in many different mammals including, but not limited to, deer, sheep, dogs and cats. When an eyeworm infects a cat, it produces a disease known as thelaziasis.

Thelazia californiensis live within the tear duct of an infected cat's eye. In a cat, the tear duct is located beneath the third eyelid, which is between the eye and the eye lid. Though they sound like they could pose a serious threat to the cat's eye and the cat's vision, these parasites are more of a nuisance and rarely cause serious disease.

How Are Eyeworms Spread in Cats and Other Animals?

The life cycle of Thelazia californiensis is relatively simple. An adult female eyeworm lays her eggs in the tears of the affected animal, which could be a cat, dog or other mammal. Inside the tears, these eggs will develop into larvae that will get eaten by flies.

The eyeworms then live for approximately one month inside the host fly. After approximately one month, the larvae relocates into the fly's mouth. At the mouth, the fly will migrate into the eye of the new host animal (in this case, the cat,) once the fly lands close enough to the eye.

Once the larvae has entered the cat, it will continue to develop for an addition three to six weeks. During this time period, the eyeworm will mature into an adult eyeworm that can begin producing new eggs, thus restarting the entire life cycle.

Symptoms and Treatment of Feline Eyeworm

The symptoms of a feline eyeworm infection are specific to the eye itself and these parasites do not cause widespread symptoms (symptoms elsewhere in the body, such as vomiting or diarrhea.)

Generally, these parasites can cause serious irritation to the infected eye, so the cat may be seen pawing at or rubbing the infected eye. There may also be an increase in tears and tear production, as the cat's body tries to naturally rid itself of the parasite.

The cat may also experience issues such as sensitivity to light or pink eye (conjunctivitis.) Should pink eye occur, the cat owner should seek the care of a trained veterinarian, as pink eye can result in more serious damage to the eye.

To identify the presence of eyeworms in a cat, the veterinarian will need to examine a sample of the cat's tears beneath the microscope to check for eggs or larvae. Once positively identified, the eyeworms can be treated either with ivermectin or with surgical removal.

If the ivermectin route is chosen, a topical anesthetic is applied to the cat's affected eye. Next, the ivermectin is inserted beneath the skin (subcutaneously.)

Additional Information:

Stanford University: Thelaziasis

Pet Edcuation: Cat Eyeworm