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About Eyeworm Infections in Assistance Dogs

About Eyeworm Infections in Assistance Dogs

Apologies to the squeamish, but today we’re talking about eyeworm infections in assistance dogs, which are exactly what they sound like: little worms living in your dog’s eyes. These parasites, also known as Thelazia californiensis and Thelazia callipaeda, are most commonly found on the west coast of the US and across Asia. Eyeworms infect dogs, cats, deer, sheep, and other mammals—including humans in rare instances.

As with any parasitic infection, eyeworms can cause symptoms that don’t just affect a dog’s quality of life, but can also interfere with a guide, hearing, or service dog’s ability to stay focused and perform her tasks. That’s why it’s important to know the basics about eyeworm infections, and to keep watch over your assistance dog’s condition and perform regular home health exams that include her eyes.

Cause of Eyeworm Infections in Assistance Dogs

Adult eyeworms live in the tear ducts and conjunctival sacs and under the eyelid and third eyelid of their hosts. These whitish, 0.5 to 0.75-inch-long worms lay their eggs in the tears of their host, where the eggs develop into larvae. From there, common house flies and other types of flies ingest the larvae, which then migrate to the fly’s eye to develop for about a month. When matured, they travel back to the fly’s mouth and wait for it to land near a suitable animal’s eye; when this opportunity arises, the adult proceeds to the new host’s eye, where it will lay its eggs and kick off the life cycle again.

Symptoms of Eyeworm Infection in Dogs

As many as 100 or so eyeworms can infest a dog’s eyes, and can sometimes even be seen traveling across them with rapid snake-like movements. Minor infections may not really cause much in the way of symptoms, but the primary symptom is probably not unexpected: irritation of the eye. Having worms living in and moving around on the eye can be quite uncomfortable, especially since these parasites have sharp serrations on their exterior. So, an infected assistance dog might be seen blinking or squinting a lot, pawing at her eyes, rubbing her face on furniture or other items, or otherwise demonstrating eye discomfort. Redness and inflammation on and around the eye is common too, as is increased tearing and sensitivity to light. The cornea can also end up opaque, ulcerated, or scarred.

Diagnosing Eyeworms in Assistance Dogs

If you notice your assistance dog experiencing eye discomfort, take a close look at her eyes. Eyeworms are visible to the naked human eye, so you can probably spot the problem. See your veterinarian right away for any eye problem, and the vet can usually make the diagnosis with a simple examination. Eyeworm eggs are also visible in the tears under a microscope.

Treating Eyeworms in Dogs

Treatment is simple and straightforward. Your service, hearing, or guide dog’s eyes are numbed with a topical anesthetic—and sometimes the dog is sedated—then the parasites are removed manually with forceps or flushed out with a sterile saline rinse. Parasiticides like ivermectin, moxidectin, imidacloprid, or selamectin are sometimes prescribed. Anti-inflammatory medications may be used to treat inflammation, while antibiotics are called for if there’s a secondary infection.


PetMD: Eyeworm Infection in Dogs

PetCoach: Eyeworm

Merck Veterinary Manual: Eyeworm Disease (Thelaziasis) in Dogs

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