The male pinworm, Oxyuris equi, is a common intestinal parasite of horses.
This parasite resides in the large intestine of horses and is found worldwide. It is 9 to 12 mm long with a characteristically long, pin-like tail with a much larger body.
Oxyuris equi has a direct life cycle and its predilection site is the large intestine. After fertilization, the gravid female migrates to the anus of the definitive host, emerges head first and lays her eggs in clumps (C) in a yellowish-grey gelatinous material on the perineal skin. After completing their egg laying, the females pass outof the anus and die. Development to the infective third stage larva takes place inside the egg and is quite rapid, taking only 3 to 5 days. The infective stage of Oxyuris equi is an egg containing a third stage larva (Egg + L3) and the definitive host is infected by ingestion.
Larvae (L3s) hatch in the small intestine, pass into the large intestine and enter the mucosal crypts of the cecum and colon. Here they molt to the fourth stage (L4) about 8 to 10 days after infection. The final molt to immature adults takes place between 45 and 60 days after infection and this is followed by a lengthy maturation phase of about 100 days until gravid females lay their eggs anywhere from 139 to 156 days after infection.
The prepatent period is approximately 5 months.
Importance is mainly limited to aesthetic considerations. Chronically infected horses have a very poor appearance. Heavy infections also cause severe irritability.
Some ulceration can result from the mucosal feeding of the larvae. Most of the clinical significance results from the intense itching caused by the sticky fluid with which Oxyuris eggs are attached to the rump. In addition to loss of condition and poor appearance, biting and scratching may cause wounds open to infection. Severe cases can lead to nervousness and anorexia. Rubbing and scratching at the perianal region cause irritation, dull hair coat, and loss of hair known as "rat-tail."
Presence of masses of whitish- yellow eggs around the anal region. Eggs are collected using transparent adhesive tape.
Cleanliness and frequent changes of bedding will restrict reinfection. Treatment will eliminate intestinal worms.