Thelaziasis: Biology, Species Affected and Pathology (Conjunctivitis): A Review

Thelaziasis is an infestation caused by the parasite Thelazia which is transmitted from one host to another host by the intermediate host face fly. Face fly is a non-penetrate secretophagic or tear feeding flies of the genera Musca. Thelazia is a genus of parasitic round worms that affects the eyes of numerous domestic animals, including cattle, dogs, cats, sheep, goats and other livestock. Many wild mammals and birds are affected as well as human. Predilection site of adult Thelazia worms are the eyes and the tissues around it. Thelazia is a creamy-white slender-shaped ectoand endo-parasite which measures up to 8-12 mm in males and 12-18 mm in females. The females are viviparous and L1, released into the lachrymal secretions of the definitive host. Both adult and larval stages live in eyes and cause conjunctivitis, keratitis, lacrimation and ocular discharge. Various clinical signs are associated with thelaziasis including keratitis, conjunctivitis, lacrimation, epiphora, photophobia and corneal opacity Thelazia infections occur seasonally and are linked to periods of maximum fly activity. Adult worms can be removed with fine forceps and by using cotton swabs under local anesthesia. Pharmacological indications include irrigation of the eyes with 50-75 ml aqueous solution of 0.5 % iodine and 0.75% potassium iodide has been recommended for T. gulosa and T. skrjabini or applied steroid ointment, fenbendazole and Ivermectin subcutaneously.