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  • Oxyuris equi

  • Part of the nematode family

  • Pinworms cause itching and irritation to the hind quarters

  • While they should be controlled by broad spectrum wormers some are more effective than others

  • Hygiene is the main factor in their control




Pinworms are located in the hind gut. The adult female migrates out of the anus to lay her eggs on the surrounding area. A sticky secretion (anal rust) can often be found under the tail indicative of pinworm presence. The anus and hind quarters will be itchy and the horse will rub shedding the eggs onto any surface or clothing it comes into contact with. The eggs then fall onto pasture and hay and the horse ingests these to become reinfected. Eggs can also be spread onto grooming kit and rugs. Grooming can then spread these eggs over the horse.  Feed, bedding and water troughs are common points where re-infection can easily occur and the cycle starts again with the horse ingesting the eggs that hatch and migrate to the large intestine.


















What do they look like?


  • Pinworms can be seen in the dung of horses where they are present, or around the anus area.

  • They are cream/white and often partly translucent

  • They look like bean sprouts

  • Males are 1-2 cm and females 10-15 cm with long tapering tails.

















What damage can they cause?


  • They cause irritation which can lead to the horse rubbing the hind quarters excessively

  • There is no evidence of an intestinal disease caused by this parasite above some low grade inflammation in the most severe of cases


Clinical signs


  • Excessive itching or rubbing of the tail/hind quarters

  • Female protruding from the anus when she is laying her eggs

  • Discharge


Diagnosis and detection


  • Cannot be detected using faecal egg counts

  • Diagnosed by the identification of parasites on the anus or eggs on the skin surrounding the anus

  • Your vet can identify pinworm eggs by collecting on adhesive tape and examining under the microscope




  • The parasites can be killed by most classes of wormers

  • Topical wash and enema


Preventative measures


Where pinworm is present the 1st step is always to follow strict hygiene protocols. Breaking the pinworms lifecycle is the most effective way to stop the problem. This is achieved by:


  • Wiping the horses anus and under tail area with a suitable mild disinfectant regularly to remove any eggs.

  • Wash rugs and grooming kit that could be a source of re-contamination

  • Cleaning down any areas the horse may have rubbed against with disinfectant to remove any eggs to prevent re-infection (don’t forget lorries, trailers, field shelters and fences as well as stable walls).

  • If hygiene alone does not break the cycle then chemical worming will also be required.

  • Chemical wormers alone will not sort the problem as the horse will continue to become re-infected by the eggs in the environment.

  • Some wormers are more effective on pinworms than others.

  • The wormers that treat pinworm contain the chemicals where resistance is developing in other species of worms. Care should be taken not to over treat pinworm as by doing this you are also over exposing other parasites to the chemicals at the same time.













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