Ringworm

What is ringworm?

Ringworm is a fungal infection in the skin caused by various dermatophyte species. In horses, the most common species are Microsporum and Trichophyton species and although these are common in horses, they are also able to infect other species, including humans. The lesions normally appear as small raised spots that lose hair, the lesions then develop to become scurfy and a thick dry scab may form, occasionally developing to become sore and itchy. Ringworm can mimic many other diseases, such as lice, bacterial infections, allergies, immunologic diseases and nutritional diseases. In lots of 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 condition is highly contagious and whole groups of horses can become affected in an outbreak and is also transmissible to humans.

How does it occur?

Ringworm is passed between horses either by direct contact, shared tack, grooming equipment, clothing or contact with contaminated fencing, stables or trailers. The fungi are quite resistant to environmental factors and can remain on fencing and timber structures for long periods (over 1 year). The fungi can remain on the skin for up to 3 weeks before clinical signs develop – therefore disease can be spread before there are visible signs of infection. Commonly it is a new horse that introduces the disease to a yard, especially younger animals because these are more likely to be affected than older animals due to having a ‘naïve’ immune system. Additionally, trauma, poor nutritional status, and impaired immunity can all result in an increased risk of ringworm infection in horses. Once horses have been infected with ringworm, they gain an immunity against it that is long lasting.

How is it diagnosed?

Because ringworm may look similar to other skin conditions, the diagnosis of ringworm needs to be confirmed by performing a skin scrape in order to collect skin cells, debris and hair for laboratory examination. This material is examined under a microscope and the ringworm spores, which are found in damaged hair shafts, can be identified by their typical appearance.  Alternatively, a test known as a PCR can test be performed on a skin scrape sample which is currently the most reliable method of confirming the diagnosis.

The fungus can also be cultured in a laboratory to identify the species involved, however this is a very slow process and may take several weeks to grow by which time 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, many ringworm cases will ‘self-cure’ in 6-12 weeks, however in most cases this is too long a time to wait due to the risk of spread to other horses. Additionally, horses with ringworm are prohibited from competing 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.

Most commonly, treatment is by washing 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 (such as Hibiscrub) 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 drying 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 veterinary surgeon. Most of these solutions and washes are not rinsed off. Smaller lesions and those on the face or other sensitive areas can also be effectively treated with creams such as those used for athletes’ foot in humans.

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 hair-less. New hair grows quite quickly. If there is any doubt, your veterinary surgeon will collect a follow-up skin scraping and, if necessary, a longer or new course of treatment should be given.

How is ringworm prevented?

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 single use disposable latex gloves when dealing with affected horses and, where possible, these horses should be dealt with last.