Oxyuris equi

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Oxyuris equi
Class Nematoda
Super-family Oxyuroidea
Species Oxyuris equi

Also known as: Equine pinworm — Pinworm — Rat-tail


Oxyuris equi is a pinworm, of the superfamily Oxyuroidea, and found specifically in horses. It is seen relatively commonly, and its presence is often a result of poor worming protocol. It is found primarily in the caecum, large intestine and the rectum.


The female worms are large, grey worms often greater than 10cm in length, with a long pointed tail. The male worms are smaller, generally less than 1cm in length.

The O. equi eggs are ovoid, and yellow. The egg shell is thick, and is slightly flattened on one side. They are 80-90µm in size.


Both the male and female adults are fixed in lumen of colon, and the caecum. After fertilization, the female migrates towards the rectum. They then lay their sticky eggs in the perineal region. After 4-5 days, the infective L3 develop. The shell then crumbles and the L3 are released into the immediate environment.

The horse then ingests the eggs containing the infective L3. These then transform into L4, and then attach to the mucosa of the intestine, and the cycle continues. The Prepatent period for Oxyuris equi is 5 months.

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