An Introduction to Equine Pinworm (Oxyuris equi)

What is pinworm?

Oxyuris equi is a common horse pinworm that affects the equine population across the world. It spends the majority of its lifecycle as an intestinal worm, but also affects the a horse’s exterior. While not as dangerous as other parasites, it can cause significant irritation.

The nematode has a direct life cycle with no intermediate host. It resides in the large intestine where, after mating, adult females migrate out through the anus to lay their eggs onto the perianal skin. The eggs are covered with a sticky fluid and after 3 to 5 days have developed into infective larvae. This is observed as white/yellow gelatinous patches on the perianal region.

How do I know if my horse or donkey is infected?

Infection with pinworm is noticed by owners due to discomfort or itching around the anal area in their horses. Recognised as pruritus, it is caused by the desiccation of the eggs and concurrent damage to the anus and tail area from scratching, causing so called ‘rat-tail’. Other signs include loss of body condition and biting or licking the perianal area. 

During this scratching behaviour, larvae are rubbed off from the perianal area and dispersed into the environment. As Oxyuris equi is a directly transmitted parasite, these larvae can infect any other equines that ingests these larvae. Shared bedding, feed and water and general objects such as gates can aid in spreading the worm. If horses groom one another, this can also spread pinworm.

How can I test my horse or donkey for pinworm?

Are you concerned that your horse or donkey has been exhibiting these mentioned behaviours? If so, our Parasitology Lab can help to identify infection. 

Collection of samples is simply done by applying sellotape or other sticky tape to the perianal area, sticking the tape to a piece of clear plastic or acetate sheet and sending it to the lab. You must also send us an email or phone to arrange payment for our services.

How can I get rid of it or prevent it from spreading?

Good management practices will be essential. If any of your animals are infected, begin by immediately housing them separately if possible. Remove all bedding, feed and water and thoroughly clean the environment to prevent infection of other animals. Make sure to clean your boots or change shoes and clothing between tending to different animals. 

For infected animals, try to remove any larvae (make you wear gloves) by cleaning the anus and tail with a suitable disinfectant. Thoroughly clean their environment including all equipment and grooming supplies. Contact your vet regarding the correct anthelmintic for your horse. 


Wolf, D., Hermosilla, C. and Taubert, A., 2014. Oxyuris equi: lack of efficacy in treatment with macrocyclic lactones. Veterinary parasitology201(1-2), pp.163-168. [Accessed 03 July 2020]