Ringworm in Horses
What is ringworm?
Ringworm is a skin infection caused by a dermatophyte (skin 'loving') fungus of that there are several different species. The fungi which cause ringworm in horses include the Microsporum and Trichophyton species, that can infect not only horses but other animal species, including humans. The skin lesions (pathological abnormalities) usually start as small raised spots from which the hair is lost. These spread from these spots and usually become scurfy or a thick dry crumbly scab may form. Sometimes the lesions are sore and sometimes itchy. In many cases there may only be a couple of lesions but if left untreated and especially if spread by grooming, the condition can become extensive. The infection is highly contagious and whole groups of horses can become affected in an outbreak.
How does it occur?
Ringworm is transmitted from horse to horse by direct contact between horses, tack, grooming equipment, clothing, contact with infested stables or trailers. The fungi are quite resistant to environmental factors and can remain on fence railings and timber structures for long periods. The most common method of spread is on tack such as bridles, boots, girths and grooming equipment. The fungi can remain on the skin for up to three weeks before clinical signs develop so the disease can be spread before there are signs of infection. Very often it is a new horse that introduces the condition to a yard. Younger animals are more likely to be affected than older ones, although very old or debilitated animals are also susceptible. Infection produces immunity that is quite long-lasting.
How is it diagnosed?
The skin lesions are sometimes but not always characteristic and may look similar to other skin conditions such as rain scald (dermatophilosis), and some cases of folliculitis. Your veterinarian can confirm the diagnosis by collecting a skin scraping in order to collect skin cells, debris and hair. This material is examined under a microscope and the ringworm spores, that are found in damaged hair shafts, can be identified by their typical appearance. The fungus can be grown in the laboratory to identify the species involved, which sometimes helps with treatment. This is done in the same way that bacteria are cultured in an incubator. Unlike most bacteria that grow very rapidly, fungi take several weeks to grow and in many cases the horse has been successfully treated before the results of the culture are known. This may nevertheless be helpful for cases that are not responding to treatment and for the treatment of other horses in contact.
How is ringworm treated?
If left untreated, most ringworm cases 'self cure' in 6-12 weeks. In most cases this is too long a time to wait because of the risk of spread to other horses. Horses with ringworm are also prohibited from competing or racing and are unable to travel abroad. Therefore, apart from the need to relieve the horse's discomfort, it makes sense to treat cases as soon as they become apparent.
There are two main forms of treatment. Most commonly, treatment is by washing or rinsing the affected areas with specific anti-fungal solutions. There are several available but no one product will successfully cure all cases and it may be necessary to try two or more different treatments before one is successful. Most of these solutions are applied on two or more separate occasions over a week or more. It is important that all scabs, scurfy skin and debris are removed before treatment is applied or the fungi will be protected from the effects of the medication. This can be achieved by washing the area with a mild detergent and gently using a nylon scouring pad or toothbrush to carefully lift the scabs and debris. If the skin is raw, extensive scab removal may need to be delayed until after the first few treatments. Rinse the skin well and allow to dry as any water on the coat will dilute the solutions further. Apply the treatment according to the directions on the pack or as instructed by your veterinarian. Most of these solutions and washes are not rinsed off.
At the end of a course of treatment, the lesions should have stopped spreading, no new lesions should appear and the skin should look healthy, if bare. New hair grows quite quickly. If there is any doubt, or if proof of freedom from infection is required for racing or transport reasons, your veterinarian will collect a follow-up skin scraping and, if necessary, a longer or new course of treatment should be given. In severe, generalized cases or where there is an outbreak in a group of horses, treatment with powders, (griseofulvin), given in the feed for 10-14 days can be used. These take up to six weeks to be effective and should be used in conjunction with topical (skin surface) treatments as described above.
Prevention and control
Where possible, new horses should be kept in isolation for 2-3 weeks and closely monitored for signs of suspected ringworm, coughing and other signs of infectious or contagious disease. If you suspect ringworm, ensure that the affected horse is treated and that it has its own grooming kit and tack, which should not be used on any other horse. Treatment should commence immediately and the grooming kit, rugs and tack thoroughly disinfected during and after treatment. Equipment used for treating the affected horse should not be used on other horses and should be disinfected or disposed of after treatment has ceased. Handlers should use gloves when dealing with affected horses and, where possible, these should be dealt with last.
Can I catch ringworm from my horse?
It is possible but uncommon for people to catch ringworm from horses. The lesions are usually itchy and red patches or 'rings' may form and can occur anywhere on the body. Your doctor should be consulted to confirm the diagnosis and for prescribing a suitable treatment.
Edited by Kim McGurrin BSc DVM DVSc Diplomate ACVIM © Copyright 2010 Lifelearn Inc. Used and/or modified with permission under license.