Life cycle of Thelazia gulosa

Thelazia gulosa can infect the eyes of cattle, bison, buffalo, and humans (1). Adult worms live under the eyelids and in the ocular tissues (eg, nasolacrimal ducts, conjunctival sacs, and excretory ducts of lacrimal glands) of the host animal (2). After mating, female worms release large numbers of first-stage larvae (3) into the lacrimal secretions of the host. First-stage larvae are then ingested by muscid face flies (4) that feed on eye secretions. In the muscid vectors, T gulosa larvae develop to second-stage and infective third-stage larvae (5), which are eventually released from the fly's proboscis onto the ocular mucosa of a new susceptible host (6).