Thelazia spp

From Cat
Thelazia callipaeda on the lateral canthus of the cornea of a cat

The 'eye worms', Thelazia californiensis and T. callipaeda are parasitic spirurid nematodes reported in the literature to infect cats[1].

These worms have been reported in the Americas, Europe and Asia, and Australia[2][3].

Burnett et al (1957) reported that the larvae from this parasite infect various species of Diptera flies (e.g. Phortica variegata). When the flies fed on fluids secreted in tears from the cat, the parasitic larvae which had migrated to the mouthparts of the flies, are passed into the cat's tear secretions and migrated onto the cornea. Adult and fourth-stage larvae can be found on the cornea, in the eyelids, tear glands, tear ducts, or nictitating membrane of the host cat.

Thelazia callipaeda infects the eyes of carnivores and humans in Far Eastern Asiatic and European countries. Studies have demonstrated the occurrence of T. callipaeda in foxes from areas where canine thelaziosis is endemic[4].

Cases of infections in dogs, coyotes, rabbits, foxes and humans have been reported. Wild fauna plays a major role in maintaining and spreading eyeworm infection in humans and domestic animals[5].

Thelazia spp cause epiphora, conjunctivitis, corneal ulcers and superficial keratitis due to actions of their migration around the surface of the eye[6]. No reports of parasites penetrating the cornea have been recorded in the literature although it has been reported in humans.

Treatment is usually limited to topical therapy with antibiotic and antiinflammatory eye ointment supplemented with appropriate anthelmintic treatment such as ivermectin topically (not on the eye).


  1. Burnett, HS et al (1957) Observations on the life cycle of Thelazia californiensis Journal of Parasitology 43:433
  2. Malacrida F et al (2008) Emergence of canine ocular Thelaziosis caused by Thelazia callipaeda in southern Switzerland. Vet Parasitol 157(3-4):321-327
  3. Barton MA & McEwan DR (1993) Spirurid nematodes in dogs and cats from central Australia. Aust Vet J 70(7):270
  4. Otranto, D., et al (2009) Thelazia callipaeda (Spirurida, Thelaziidae) in wild animals: Report of new host species and ecological implications Export. Veterinary Parasitology 166(3-4):262-267.
  5. Otranto D et al (2003) Current status and epidemiological observation of Thelazia callipaeda (Spirurida, Thelaziidae) in dogs, cats and foxes in Italy: a "coincidence" or a parasitic disease of the Old Continent? Vet Parasitol 116(4):315-325
  6. Dorchies P et al (2007) First reports of autochthonous eyeworm infection by Thelazia callipaeda (Spirurida, Thelaziidae) in dogs and cat from France. Vet Parasitol 149(3-4):294-297