Itchy Bum? It May Be Time To Test For Pinworm

What is pinworm?
Concern about cases of pinworm (Oxyuris equi) in horses has been on the increase over the last few years.

Although pinworm isn't a major health threat to your horse like other worms can be, infection can cause irritation. Sometimes that can be so severe that horses will rub themselves raw around their rear, hind legs, and the top of their tail. This can lead to skin infections, minor to major discomfort, and depression. As the female pinworms travel to the anus to lay their eggs, they can often be expelled in dung which can be easily detected whilst poo-picking or mucking out your horse’s stable.

The life cycle of the pinworm is different to a lot of the other worms found in the horse’s gastrointestinal system.

Pinworm eggs are ingested by the horse, usually from contaminated surfaces where an infected horse has rubbed themselves in discomfort and deposited eggs.
These hatch within the horse to live in the intestine as larvae and eventually mature into adults. There is no intermediate host and no migration through any other organ in your horse’s body and the worms themselves are relatively harmless whilst living in the horse.
The female pinworms venture out of the rectum to deposit their eggs on the skin surrounding the anus area. The eggs are contained in a sticky, yellowish residue which can sometimes be seen under the tail of infected horses, especially in severe cases - It's thought to be this residue that contributes to the discomfort and itching that is seen in infected horses.
The life cycle of the pinworm is relatively long; worms can take up to five months to mature after they have hatched from their eggs. Immature stages of the worm are less sensitive to wormers so may survive post treatment – which is why regular testing is important for horses who are susceptible to pinworm infection.

How Do I Test For Pinworm In My Horse?

It is important to note that pinworms are not the only cause of itching in horses; moulting, mites, lice, seasonal sweetitch, roundworm infestation, allergies, bacterial and yeast infections or other skin complaints can all cause itching around the hind end and tail area. To determine if pinworm is the cause of your horse’s itching and discomfort there are a number of things you can look for.

Pinworm eggs are unlikely to show up on a faecal worm egg count. Although the worms live in the intestinal tract, the eggs are laid externally so are not detected in a faecal sample. An adhesive tape test can be carried out to look for the presence of the parasite eggs. While this is not a definitive test it gives us one of the best chances of confirming infection in individual horses.

Female worms can sometimes be seen in the dung of infected horses when they are passed out whilst coming to lay their eggs. They almost look like white beansprouts with a distinct point to one end so are usually easy to see in infected horses. Look for a yellow sticky residue under the tail of your horse which the eggs are laid in – confirm the presence of pinworms in individual horses by carrying out an adhesive tape test.

To test for pinworm, you can take an adhesive tape impression from under the horse’s tail.

Collect the sample in the morning, ideally before 9am if you can. Pinworm are most active at night so this will give the best chance of detecting any activity that is present.
Take a 4” length of clear sticky tape and press this firmly onto the skin around the anus – ensure that the tape touches the skin and not the hair.
Fold the tape in half, sticky side to sticky side.
Pop the folded piece of tape into the sample bag provided with your testing kit ensuring this is clearly labelled with your horse’s name.
Post to Westgate Labs in the prepaid envelope with your completed paperwork including your name and contact details.
The sample will be put under the microscope in the laboratory to look for the presence of pinworm eggs.
Westgate and Supplement Solutions will work together to email you your results and advise on the best treatment option for your horse.

My Horse Has Tested Positive For Pinworm, What Do I Do Now?

Pinworms can be a difficult problem to get rid of once your horse has become infected. If an infection is confirmed by an adhesive tape test, then it is recommended to use either Pyrantel or a 5-day course of Fenbendazole.

Ivermectin and moxidectin are also licenced against pinworms (Oxyuris equi), but anecdotally have been found to be less effective. The worming treatment should always be administered orally to your horse, ensuring that you follow the instructions on the data sheet as closely as you can. This best targets the worms in the digestive tract as this is where they live and mature.

There has previously been some advice suggesting the wormer to be administered into the anus or applied to the skin around the anus area of the horse. This is not a recommended treatment regime as it will have very limited, if any effectiveness on the pinworm. By using worming treatment around the anus area, additional chemical will be put into the environment with eco-toxic consequences which is bets to be avoided where possible. As faeces is passed out of the rectum through the anus, this will quickly sweep any wormer administered here with it, so will do nothing to target the pinworm population in the horse's digestive tract.

The female pinworms that travel from the colon and through the rectum to lay their eggs outside the horse will die naturally as they cannot survive once outside of your horse’s digestive tract.

Treatment should be combined with incorporating increased measures of field and stable hygiene to remove as many eggs from the environment as possible to prevent reinfection to your horse or to any other horses in the herd.

Clean around your horse’s anus area once or twice daily to remove any eggs that have been laid here.
Apply petroleum jelly, coconut oil, or something similar to the area to help prevent eggs sticking to your horse and also soothe the area.
Clean and disinfect any areas where infected horses may have rubbed, such as gate posts, fencing, stable doors or mangers, field shelters, and walls every few days. Remember you can't disinfect a dirty surface! Ensure that you wash the areas with an eco-friendly detergent (link this to our website: https://www.supplementsolutions.co.uk/equine/field-stableyard?my_horse_has=2236) before using a good veterinary disinfectant that is safe for animal use. It is advisable to do this every few days, or as often as you can, until you can be certain treatment has been effective.
Pinworm tends not to infect a whole herd kept together so blanket treatment is rarely required. It is advisable to test individual horses and treat each according to their test results. Like all parasites some horses tend to be more susceptible than others to pinworm infection - often young or older horses will be more likely to become infected. Supporting their immune system, addressing any underlying health problems, and ensuring that they are happy in the herd will give them as much resilience as possible.
Adhesive tape test again two weeks after treatment. If any eggs are present the treatment hasn't been fully effective so another course may be necessary, and you may want to consider using a different active ingredient under the advice of your vet or SQP. For persistent cases you may need to contact your vet who is able to prescribe anthelmintic treatment at shorter intervals than your SQP.