Ringworm in horses is a highly contagious fungal infection of the skin that can spread rapidly from horse to horse, or from horse to human. Confusingly, despite the name, ringworm is not always ring-shaped and has nothing to do with worms. The Trichophyton spp. and Microsporum spp fungi that cause the disease flourish in wet British winter weather. They grow across the surface of the skin and around the hairs, producing a variety of changes affecting the horse’s coat and skin.
Signs of ringworm in horses
Often all that is noticed in the early stages is tufts of hair that may appear raised up from the rest of the coat with a slight swelling underneath. People expect ringworm patches to be circular, but they can be any shape. Usually, the tufts of affected hair fall out, leaving the skin underneath looking raw and sore. Classically, ringworm develops into grey, flaking areas with broken hairs, but the coat will gradually regrow over the next month.
Ringworm can appear in many different disguises. If your horse has a skin rash, sore or bald area for which there is no other obvious explanation, you should have him checked and treated for ringworm to reduce the risk of the infection spreading further.
Ringworm can appear anywhere on the body, but the most common sites are where the skin is in contact with the tack or harness, such as the saddle or girth areas. Any rubs or tiny abrasions on the skin can give the fungus an opportunity to invade the skin. Young horses are typically more at risk, probably because they have less immunity. Older horses usually have more mild signs of ringworm and recover more quickly.
Is it serious?
Horses do not die from ringworm so a case is not a crisis, but it is highly contagious and can spread rapidly from one horse to another – as well as to humans and other animals – if you fail to take suitable precautions.
The infection spreads either by direct contact, or on tack, rugs, grooming kit or buckets. Also the ringworm fungus will produce spores that can remain dormant on woodwork for more than a year, contaminating stables and fencing.
Horses with active ringworm should not travel as they spread the condition, so training and competition schedules can be interrupted, so the quicker you act, the less impact it is likely to have. Racehorses with dermatitis (skin disease) that may be ringworm require a veterinary certificate that they are not contagious before racing.
During an outbreak
If you suspect that your horse has ringworm, you should carry out the following control measures.
- Keep any suspected cases separate in their own stable. If an infected horse is isolated he should not spread the infection, provided he cannot touch other horses and care is taken in handling the potentially affected horse
- Do not groom or clip an affected horse because of the risk of spreading spores
- Wear protective clothing and disposable gloves when handling the affected horse
- Avoid riding an affected horse. This reduces the chance of spreading the infection and prevents skin sores from being rubbed by the tack
- Do not share rugs, tack or grooming kit – girths are a common item on which ringworm can spread
- Treat your riding boots/half chaps/gaiters to avoid spreading to another horse
- Ask your vet to check any suspected horse
- Treat your horse, his stable, and if relevant the horse’s lorry or trailer
Your vet may be able to diagnose ringworm from looking at the skin lesions, particularly if several horses are involved. Frequently, laboratory tests are needed to be certain: samples are examined under the microscope for fungal spores. Sometimes, a culture of the fungus is required, which means it can take 10 days or more before the vet has a definite answer, but a test to detect the fungus DNA in hair samples1 has been developed that gives results much more rapidly, usually within 24hours.
Horses can catch ringworm from other animals, particularly cattle or dogs, but they can also pass it on to humans. It is one of the few conditions you can catch from your horse, so for that reason alone, the infection needs to be treated seriously.
Treatment for ringworm in horses
The incubation period for ringworm is between one and four weeks. Following infection, lesions usually appear within 7 to 21 days depending largely on the immune status of the horse. If left, most cases will eventually clear up, but prompt treatment is recommended to avoid it spreading further. The aim of treatment is two fold: first, to kill the fungus and second, to destroy the infective spores. It is important to cure the infected horse, but also vital to reduce the environmental contamination.
To treat the horse, there are a number of effective washes, shampoos and sprays that can be applied to the skin. The whole horse should be treated initially, then any areas that show clear signs of infection as suggested by your vet. Disposable gloves should be worn while treating the lesions and you should clean your hands with a suitable wash afterwards. Your vet may prescribe an antifungal powder to feed to your horse, but as there is minimal evidence that this in-feed medication is effective, it is no longer regularly prescribed. If used, care must be taken as it is dangerous for both pregnant women and mares.
It is wise to isolate affected horses and ponies as much as possible to limit environmental contamination. Any stables involved should be cleaned thoroughly and bedding destroyed. You should disinfect the rugs, fences and anything else a horse with ringworm has contacted.
For a disease that is non-critical, this may seem a lot of trouble, but one intensive treatment blitz can reduce the spread among horses in the immediate area. Wooden stable walls are an ideal place to harbour ringworm spores. A variety of effective compounds are available for use on tack, rugs and grooming kit without causing damage. Environmental treatment can be complex as the products can be irritant and/or toxic. It is best to seek advice from your vet as to what is most appropriate and safe for your situation. Options may include five to 10 per cent bleach for concrete. Historically creosote was used for wood but is no longer available, so take expert advice rather than use the wrong product, since the fungal spores are resistant to many treatment options.
If a large stable yard needs to be treated, horticultural foggers, containing anti-fungal agents, can be used. This may be useful for special items such as your best rug and saddle, which cannot be treated with a harsh disinfectant.
A vaccination against ringworm2 is available in some countries, but it is not licensed in the UK.
If untreated, a case of ringworm in a single horse will typically resolve itself over a few months, leaving the horse with a level of immunity against future cases of the same type of ringworm, but not all fungal skin diseases. Any damaged skin will return to health and any missing hair will regrow with time, although sometimes a difference in hair colour may be apparent for some time.
Due to the highly contagious nature of the fungus, in both the host species and others, and it’s ability to contaminate the local environment, it is strongly recommended that owners act quickly and robustly to deal with any ringworm cases.
- Equine test enables same-day ringworm results 23 February 2017
- Immunoprophylaxis of dermatophytosis in animalsNovember/December 2008
Also: Dermatophytosis (ringworm) 5 January 2010
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