Ringworm

Dermatophytes, microscopic fungii, are the agents responsible for ringworm (also known as dermatophytosis) in horses, especially the Microsporum and Trichophyton species. The most common species encountered is Trichophyton equinum.

The species which most often affect horses are different from those affecting other animals or humans. Ringworm in horses is therefore seldom spread to Man.

These fungii form filaments which colonise the skin and the hair follicules. They then produce spores measuring a few micrometers in diameter, these are the contagious elements.

Ringworm is spread via the spores :
    • By direct contact between an infected horse and another,
    • Indirectly : via the environment, contaminated equipment or Man.
The spores can survive for long periods in the outside environment.

Contamination is higher when there are prior skin lesions (presence of lice, sores due to tack rubbing….).

All horses can become infected but young horses (< 2 years old) are more at risk of developing clinical signs. Horses confined in groups inside also appear to be more at risk. Competitions and gatherings of young horses are also conducive to the spread of the infection.

Ringworm can appear all year round, but is more frequently encountered in autumn and winter.

Once horses have been infected, they are rarely infected a second time, except if the dermatophyte involved is of a different species.

After an incubation[1]period of between 1 to 6 weeks, ringworm first shows as small bumpsin the skin of 2 to 5 mm in diameter, or raised hair on a circular area of around 5 to 20mm in diameter. More seldom a generalised skin rash like urticaria is observed. The lesions will generally evolve towards round bare patches with grey scurfy skin. Clinical signs are however variable.

There are often multiple lesions located near the head, neck and thorax.

Ringworm does not usually cause itchiness, except in the following cases :
    • When associated to other parasites (lice for example),
    • In case of secondary bacterial infection.

[1] incubation period = lapse of time between infection and appearance of the first clinical signs

Ringworm in pictures :

Clinical signs and the contagious nature of the infection will usually orient the diagnosis. However, ringworm is probablyover-diagnosed, and should not be mistaken for a bacterial infection such as rain-scald for example. To obtain a reliable diagnosis, a skin and hair sample should be taken from around the lesions, and it should then be examined for the presence of dermatophytes. The laboratory will then carry out an examination under the microscope, or grow a culture.

Most of the time, ringworm will self-heal in a few weeks or months, but contamination of all the horses in the yard is then possible. Therefore it is advisable to treat as soon as the first symptoms appear, to avoid the spread of the infection.

Affected horses should be isolated, and the grooming and stable equipment or tack should not be used on other horses. It is also preferable to deal with affected horses last, or to wear gloves when taking care of them.

Local treatment using an anti-fungal solution (especially enilconazole) applied with a sponge is the most frequently used. The whole body should be treated, even if the lesions are localized. Several treatments are needed. Although the solutions used are not toxic for Man, it is recommended to wear gloves when treating the horse, or at least to wash your hands after treatment.

Griseofluvin based oral powders can also be used and given in the feed.

Get advice from your veterinarian.

Dinsinfecting the environment, with an anti-fungal solution active against spores (e.g bleach) and theequipment (soaking in the anti-fungal solution), is essential.

Prevention is ensured mostly by applying strict hygiene measures :

• Use individual grooming material for each horse, as well as individual saddle pads and rugs, which should be washed regularly with anti-fungal washes. Wherever possible also use individual tack (head-collar, bridles, girths and harness…). These recommendations are all the more important when at competitions or other shows.
• When a new horse is introduced to the yard, a quarantine period should be respected .