Thelazia lacrymalis: Eyeworm

General Description: The long slender adult worm may reach 18 mm.

Life Cycle: The viviparous female worm sheds larvae into the tear secretions. Larvae picked up by a specific face fly, the intermediate host, are infectious after 30 days. At this time they migrate to the fly mouthparts and into the eyes of horses when the fly feeds.

Location:: The adult inhabits the tear duct and conjunctival sac.

Geographical Distribution: Worldwide.

Significance: Heavy infections cause damage and annoyance to the host.

Effect on Host: Low worm burdens cause mild eye irritation and conjunctivitis. Heavy infections result in corneal vascularization, secondary bacterial infections, and occasional blindness.

Diagnostic Information: Observation of adult worms in the eye, or identification of larvae in the tears.

Control: The adult worms can be removed under local anaesthesia. Fly populations should be controlled with insecticides, sanitation, and screening.