Affects: Cats, Dogs
Thelaziasis is the term for infestation with parasitic nematodes of the genus Thelazia. The adults of all Thelazia species discovered so far inhabit the eyes and associated tissues (such as eyelids, tear ducts, etc.) of various mammal and bird hosts, including humans. Thelazia nematodes are often referred to as "eyeworms".
Signs And Symptoms: In animal and human hosts, infestation by Thelazia may be asymptomatic, though it frequently causes watery eyes (epiphora), conjunctivitis, corneal opacity, or corneal ulcers (ulcerative keratitis). Infested humans have also reported "foreign body sensation" – the feeling that something is in the eye.
Diagnosis: Diagnosis involves simply examining the eyes and nearby tissues for the worms. Adult Thelazia are very active; one author described T. californiensis as a "short lively piece of nylon fishing line about 10 mm long."
Treatment: Because they live so close to the outside of the body, Thelazia is one of the few nematode infections which can be treated topically.
Topical treatment of livestock, dogs and cats with organophosphates (such as ecothiopate iodide or isofluorophate) and systemic treatment with anthelmintics (such as ivermectin, levamisole, and doramectin) are recommended by the Merck Veterinary Manual. Other sources have reported positive results treating dogs with moxidectin, imidacloprid, or milbemycin oxime.
For the treatment of human cases, removal of the worm is suggested. Topical treatment with cocaine or thiabendazole have also been reported to kill the worms in human cases. Because most, if not all, species of Thelazia are spread by flies, sanitary practices which reduce the presence of flies will also reduce the spread of thelaziasis.
In canines, prevention against canine thelaziosis by monthly administrations of a combination of milbemycin oxime and afoxolaner (NexGard Spectra) has been found effective.