Pinworm (Oxyuris Equi) are small white worms that can cause itching of the skin around the horse's dock. Pinworm infections were previously uncommon because the worms were easily controlled with most treatments and seemed to only affect young horses. Recently pinworm infections have become more common, now affecting older horses and are more resistant to some wormers.
Usually only one or two horses in a group are affected. They itch due to the horse's reaction to the worm eggs that are laid on the skin around the dock area. The itching can be unpleasant and is sometimes confused with sweet itch. To confirm the diagnosis we use a microscope to look for signs of the pinworm eggs, having initially collected a sample. Sometimes we see the adult worms in faeces; these are white with a very long, thin tail (pin-shaped) and can be up to 15cm long. Unfortunately, pinworm eggs cannot reliably be seen in faecal worm egg counts.
Treatment requires good hygiene and use of wormers. Daily washing of the affected skin with mild detergent can remove the parasite eggs. Barrier creams such as vaseline can help to prevent new eggs from sticking. Cleaning of the stable or areas that the horse itches against can help remove eggs and reduce re-infection. Hygiene is most important, as on many occasions wormer medication is ineffective.
Some wormers still appear effective but we often treat affected horses more frequently. Some people suggest that wormers should be given directly into the rectum but this will not work.
If you think your horse may have a pinworm infection, please contact us for further advice.