Thelazia spp

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

Thelazia are a species of nematode worm which parasitizes mammals. Commonly referred to as the eye worm, these nematodes occur in the Americas, Europe and Asia, but not Australia.

Two species, Thelazia californiensis and T. callipaeda have been reported in the literature to infect cats[1]. Burnett et al (1957) reported that the larvae from this parasite infect various species of Diptera flies. 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[2].

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.

Clinical signs

Thelazia spp cause conjunctivits and superficial keratitis due to actions of their migration around the surface of the eye. No reports of parasites penetrating the cornea have been recorded in the literature although it has been reported in humans.

Treatment

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).


References

  1. Burnett, HS et al (1957) Observations on the life cycle of Thelazia californiensis Journal of Parasitology 43:433
  2. 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.
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