Pinworm is a white/ grey worm which colonises in the rectum of infected horses. The worm gets its name from their long tale which tapers to a point, the females can reach up to 4 inches in length, the males are much smaller. The larvae feed off the mucosal lining of the intestine, once they mature into adults the female worms then pass through to the rectum and anal area where they proceed to lay their eggs.

There has been a higher prevalence of pinworm reported in the past few months. Unlike the resistance problem which is being seen with other species of worms and chemical wormers, the pinworm problems seems to be because the wormers are too good. The wormers being used are absorbed so well by the front part of the gut, that it is not reaching the hind gut where pinworm causes problems, and therefore sufficient quantities of chemicals are not killing the pinworms.

How do I know if my horse has pinworm?

  • Momentary protrusion of a worm through your horse's anus, this is when the female lays her eggs, she will then disappear back in to the rectum. An adult female can lay up to 60,000 eggs per day.
  • Eggs will appear in a gelatinous mass around the anus.
  • Skin irritation around the anus area
  • Rubbing of the tail/ anus area
  • Biting and licking of hindquarters
  • Behavioral changes including loss of appetite and nervousness
  • Signs are similar to horses with sweet itch

How is pinworm passed from horse to horse?

  • Ingestion of eggs through mutual grooming
  • Ingestion of eggs which have fallen on to the pasture
  • Ingestion of eggs which have fallen in to drinking water/ feed
  • Contaminated environments e.g. fence posts/ stables
  • Contaminated grooming kits

How is pinworm treated?

  • Pinworm is not easy to get rid off. Good management practices are essential.
  • Thoroughly cleanse the anus/ tail other affected areas to remove eggs by using disposable wipes/ warm diluted disinfectants (suitable for use in these areas)
  • Disinfect grooming kits, do not use same grooming kits on infected and uninfected horses
  • Remove bedding and disinfect and pressure wash stables/ water buckets etc
  • Clean drinking troughs regularly
  • Seek advice on chemical wormers required to treat horses identified with pinworm

How to test for pinworm?

  • Examination of a sample of specially prepared droppings under a high-powered microscope
  • Application of sticky tape to the skin around the anus and then examining this under a microscope
  • Due to the eggs being laid around the anus area, the eggs are not expelled in the dung and therefore are not detected in faecal egg counts
Please note these tests can only be carried out by a vet.