Pinworm (Oxyuris equi)

Less common than some of the others, the Pinworms are not thought to be harmful but can provoke irritation around the tail.

Oxyuris eggs

Adult oxyuris

Pinworms inhabit the large and small colon and have a relatively simple life cycle.  The females lay their eggs around the anus of the horse using a sticky substance, which is irritating to the horse.  The eggs are dislodged as droppings are passed or fall onto the pasture where they are eaten by horses, thus completing the cycle.