(Oxyuris Equi)
Adult pinworm emerging to lay eggs
The pinworm lives in the large intestine and passes out of the anus to lay its eggs.
The pinworm is a grey/white worm with a long tail, which tapers to a point. While the male is significantly smaller, the female pinworm can reach up to 20cm in length.
Although pinworms live in the large intestine and colon, the adult worm emerges at night to lay eggs on the skin around the rump. After laying her eggs, the female pinworm will then return inside the rectum. A female pinworm can lay up to 60,000 eggs per day.
The pinworm can cause severe itching around the anus which can occasionally lead to self-trauma.
Pinworms cause irritation to the horse. Look out for rubbing of the rear end against fences, which can result in damage around the anus.
Biting and licking of hindquarters may also be observed. There are no eggs on faecal examination. However, eggs may be seen in a gelatinous mass around the anus.
Sellotape can be gently pressed on the skin around the anus to pick up eggs and if present a number of treatments can be used.
No eggs will be found on a faecal worm egg count as the adult female worm crawls out of the anus to lay eggs.
Pinworm - treatment options and resistance
| Fenbendazole | Pyrantel | Ivermectin | Moxidectin | Praziquantel | ||
|---|---|---|---|---|---|---|
| Oxyuris equi | Considered the most effective treatment Clinical responses may still be poor |
Considered effective Clinical responses are often poor |
Resistance suspected but not yet confirmed in the UK Clinical responses are often poor |
Resistance suspected but not yet confirmed in the UK Clinical responses are often poor |
Not indicated | |
Source: Canter Guidelines
Remains effective for indicated use
Resistance emerging or suspected
Some resistance reported – FECRT should be performed
Resistance common – should only be used with supportive FECRT results
Not indicated for use for treatment
