Management of the horse with pinworm

The equine pinworm, Oxyuris equi, is commonly occurring in horses across the world. The life cycle begins when a horse ingests an infective, larvated egg from the environment. The eggs hatch in the small intestine, and third-stage larvae then invade the crypts of Lieberkühn in the cecum and ventral colon. After about 3–11 days, larvae emerge from the crypts as fourth-stage larvae that attach to the mucosa of the ventral colon. After approximately 50 days, the larvae then moult to the fifth stage and full sexual maturity is reached after an additional approximately 100 days. Adults primarily live in the right dorsal colon, but may inhabit more proximal sections if worm burdens are large. Gravid female worms can be found only transiently in the small descending colon and rectum and only when laying eggs in the perianal area. This author has conducted hundreds of parasitological necropsies on equines and actually never encountered a single Oxyuris specimen from these latter compartments. Female pinworms deposit their eggs in a single mass containing 8,000–60,000 eggs contained in a thick proteinaceous fluid. The available evidence suggests that these females die in the process ...