Pinworm - Donkey

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Pinworm - Oxyuris equi


Oxyuris equi, the equine pinworm, is a well known equine parasite with a worldwide distribution. They are commonly called pinworm because of the sharp, tapering tails of the females measuring up to 15 cm long. Adults primarily live in the right dorsal colon but may inhabit the proximal sections of the large intestine if worm burden is high. The characteristic feature of this parasite is that gravid female worms migrate to the anus to deposit their eggs in sticky clumps seen grossly as a yellowish white or light orange gelatinous streak on the skin of the perianal region. Although some mucosal damage caused by the feeding habit of L4 were reported, a more important effect of this parasite is the perianal irritation and anal pruritis caused by the adult females during the egg laying process. Although a well know equine parasite, O. equi received little attention because it was relatively non-pathogenic and could be controlled satisfactorily by routine anthelmintic therapy. However, in recent years, it appeared to exhibit a dramatic change in its biology and anthelmintic susceptibility. This once rare parasite seems to be on the increase in donkeys in the UK.


This is often based on clinical signs and the recovery of eggs from the perianal skin. Sometimes adult worms can be seen passed in the faeces.

Clinical signs

Tail-rubbing accompanied by broken hair shafts, or excoriated skin on the rump or base of the tail is a frequent diagnostic feature. Donkeys do not, however, appear to demonstrate this behaviour as frequently as horses. The intense itching often leads to restlessness and impaired feeding, causing some loss of condition.

Laboratory tests

Unlike other nematode parasites of donkeys and horses, pinworm eggs are rarely observed in faecal samples due to the unique egg-laying behaviour of the females. However, O. equi eggs can be collected by pressing clear sticky tape onto the perianal skin and applying the tape to a glass slide for direct microscopic observation.


Anthelmitics that have demonstrated efficacy against larval and adult O. equi in horses include ivermectin, moxidectin, fenbendazole and mebendazole. Pyrantel has demonstrated efficacy against adult stages only. Recently there have been a number of unpublished and some published reports of reduced anthelmintic efficacy against O. equi in horses. The Donkey Sanctuary has also experienced a lack of response to treatment with both ivermectin and pyrantel in donkeys. Therefore, this must be taken into consideration while treating. In addition to anthelmintic treatment, where animals are showing clinical signs such as clumps of eggs in the perineum, it is advisable to clean up the perianal region and underside of the tail using disposable cloth to remove egg masses.


Apart from a routine anthelmintic programme the practice of good hygiene to reduce environmental contamination by infective eggs is very important. The most likely sources of infection and transmission include feeding areas, water dispensers, troughs, stall litter and any communally used rubbing posts. Therefore, any comprehensive approach to combating O. equi infections must include serious efforts to keep these items and areas as clean as possible. This could be achieved by periodic steam-cleaning and use of strong disinfectants after removal of any bedding.

Literature Search

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Pinworm in donkeys publications


  • Trawford, A. and Getachew, M. (2008) Parasites In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 6
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