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Ringworm: a fungal skin infection affecting horses – and humans *H&H Plus*

Karen Coumbe Karen Coumbe

    • This fungal skin infection comes in many guises and can be tricky to identify, explains Karen Coumbe MRCVS

    IF your horse develops a skin rash or a sore or bald area for which there is no other obvious explanation, it could well be ringworm. This highly contagious fungal infection flourishes in cool, wet weather and can spread rapidly between horses – and also to humans.

    Confusingly, ringworm is not always ring-shaped and has nothing to do with worms. Instead, it grows around the hairs, slowly damaging the horse’s coat and underlying skin, yet is rarely itchy.

    Ringworm that is not rapidly identified and treated is more likely to spread. The classic example is the horse that arrives at the yard with a rough coat with patches of hair standing on end, or other signs not recognised as ringworm. Clipping him to remove such blemishes will result in rapid dissemination of the fungal spores.

    Ringworm can spread to horses from other animals, particularly cattle. While not fatal, it will disrupt riding and training schedules – especially if lesions occur in the saddle and girth regions.

    Individual yards have different policies for dealing with the disease. Some recommend strict isolation of all ringworm suspects, whereas others – especially yards with multiple young horses – take the view that it is best left to run its course.

    Untreated ringworm in a single horse will typically resolve itself over a few months, leaving him with a level of immunity against the same ringworm type (but not all fungal skin diseases). The major disadvantage is that his environment will become contaminated, so any new arrivals risk developing the disease.

    Ringworm can appear anywhere on the body, but is most common where the skin is in contact with tack. Any rubs or tiny abrasions give the fungus an opportunity to invade. Young horses are at greater risk, probably because they have less immunity. Older horses usually have milder signs and recover more quickly.

    The early stages, when tufts of hair may stand up with a slight swelling underneath, can be confused with urticaria or some other allergic reaction. Usually, the affected hair falls out to leave raw, sore skin underneath. While these areas typically become grey and flaky, the coat will gradually regrow over the next month.

    Infection spreads either by direct contact or on tack, rugs, grooming tools and yard equipment. Spores can remain dormant on woodwork for more than a year, contaminating stables and fencing.

    Fighting fungus

    YOUR vet may suspect ringworm from looking at the skin lesions, particularly if several horses are involved. Laboratory tests may be required for conformation, so that samples can be examined microscopically. Fungal cultures can be performed, but results may take a long time.

    More recently, tests to detect fungal DNA in hair samples have become widely available and offer more rapid results, usually within 24 hours.

    Following infection, lesions usually appear between seven and 21 days, depending on the horse’s immune status. Treatment aims are twofold: first, to kill the fungus and then to destroy the spores.

    Specialist shampoos and washes are best used by treating the whole horse, to reduce spore contamination, before focusing on the obviously infected areas.

    There is minimal evidence that in-feed medication is effective, so this is no longer used. A ringworm vaccination is available in Europe but not licensed in the UK.

    Various products are available for use on tack, rugs and grooming kit, without causing damage. While environmental treatment can be complex, one intensive blitz will reduce long-term spread. Consult your vet as to what is most appropriate and safe for your situation.

    How to stop the spread

    1. Keep a suspect horse isolated and don’t groom or clip him until you know it is not ringworm – ask your vet.
    2. Avoid riding an infected horse – this helps to minimise the spread and prevent tack rubbing his sore skin.
    3. Wear protective clothing and disposable gloves when handling him, seeking prompt medical advice if you develop a rash.
    4. Treat the horse as well as his stable and lorry or trailer. Remember your riding boots and half-chaps, too, to avoid cross-infection.
    5. Avoid sharing rugs, tack or grooming kit at the yard. Girths are a common cause of ringworm spread.
    6. Check competition rules – the British Horseracing Authority, for example, prohibits horses with active lesions from attending a racetrack.

    H&H Vet Clinic 29 October 2020

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