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Saturday 1st August 2015

Pinworms in horses

Published on July 26, 2012

Not easy to treat and causing rubbing of the tail head and hind quarters, pinworms in horses have been prevalent recently.

Oxyuris equi, also known as pinworms, are becoming increasingly problematic in recent months.  Adult pinworms live in the last portion of the large intestine, with the females passing towards the rectum to lay their eggs, attaching them on the perineum, the skin around the anus.  Within a few hours of being deposited here, they develop into embryos and are infective in 4-5 days. 
Within the intestine, adult pinworms have little significance.  It is the perineal irritation after the egg laying which causes an affected horse to rub their tail and anal regions, resulting in balding patches in these areas.

The issue of these worms comes from the difficulty in treating them.  Most broad spectrum wormers are recommended for treatment of pinworm.  However, due the location of the worm and that wormers are given orally, the amount of active drug reaching the rectum is so small, if any at all, that the worms are not being effectively killed.

Clinical Signs:
• May see the female worm protruding from your horses anus for short period of time as she lays her eggs, before disappearing back into the rectum
• Large egg burden will appear as a white to yellow, crusty mass around the horses anus
• Biting and licking of hindquarters
• Skin irritation around anus
• Rubbing tail and surrounding area
• Bolding patches and broken hairs on tail and around anus
• Similar signs to sweet itch except no clinical signs around the mane

Transfer of pinworm:
Pinworm can be transferred from horse to horse in a number of ways
- Mutual grooming resulting in ingestion of eggs
- Ingestion of eggs off the pasture, in drinking water or in feed
- Contamination of the environment eg fence posts / stables, where affected horses have rubbed themselves
- Contamination of grooming kits

How to test for pinworms:
Faecal egg counts will not reveal pinworm infection due to the eggs being laid around the anus and not expelled in the faeces.
A specially prepared faecal examination may reveal pinworm infection
A more reliable method of diagnosis is to make a sellotape impression from the perineum for examination under a microscope.
To do this, cut a piece of sellotape approx 10cm long.  Place on skin around anus and apply pressure to collect samples off the skin.  Repeat in 3-4 locations around the perineum and then stick onto a microscope slide, sticky side down.  Fold ends of tape around end of slide to secure. 
You can collect microscope slides from Parkside to collect samples yourself and then drop the slide in at Kings Cross Road for assessment.  We will contact you within 24hours with results.

In addition to orally administering double dose pyratape P wormer, good control of pinworm is achieved by a topical wash and enema.  This must be coupled with careful attention to environmental control. Careful disinfection of stables or fence posts where affected horses have been rubbing should be carried out and grooming kits should not be shared. 
After treatment, a repeat sellotape slide should be taken 2 weeks later to ensure egg numbers are reducing or gone.  For monitoring after a current infestation has resolved, samples can be made every 6 months for assessment.

Prevention / Control on your yard:
If you have had an issue with pinworm in the past or are currently having issues with it, best practice is to collect sellotape-slide samples from all horses for examination.  The infected ones can then be treated accordingly. 
As a further step in the quarantine process of all new horses onto a yard, they should all have a sellotape sample collected and examined before they are put into shared fields etc.

You can download a print of this article HERE