Common skin signs, like crusting, scaling and hair loss, may be the consequence of fungal skin infection such as ringworm. When present, ringworm can affect numerous animals; outbreaks in racing and riding stables can be expensive to manage and can affect competition plans for prolonged periods (racehorses cannot appear at a racecourse with active lesions). It is important to identify the condition and to limit spread as much as possible.
What is ringworm?
Ringworm is a highly contagious, superficial fungal skin infection, due to dermatophyte fungi (dermatophytosis). It is one of the most common infectious skin diseases of horses and can spread to other in-contact animals and humans. Clinical signs include scaling, crusting and hair loss, most commonly where tack causes skin trauma (girth, saddle region, neck and head).
Ringworm can affect horses at any age but younger horses in groups, as well as older and immunocompromized animals, are most at risk. Some immunity develops with age, but horses can be re-infected.
What causes ringworm?
Several dermatophyte species can cause the disease. Most commonly Trichophyton spp and Microsporum spp fungi are involved. Damage to the skin, which may only be very slight, allows infection to access the outer layer of skin and hair follicles. Poor hygiene, overcrowding, tack rubbing and ectoparasites (such as lice) are predisposing factors for the infection of hair follicles. There is an incubation period of 2-3 weeks, which means that other horses may have been infected by the time the first signs of infection are seen.
The infection causes skin inflammation and hair loss.
How will I know if my horse has ringworm?
Ringworm may initially present as small circular patches of erect hairs, which progress to pustules, crusts, scaling and hair loss. This usually occurs in areas of tack rubbing or insect bites thus the whole body can be affected, with face, neck and girth region most commonly involved. There may be single or multiple lesions, which can be clustered or widespread. If lesions coalesce, the typical circular appearance is lost. Some lesions may be painful and leave a wet oozing surface when the hair is pulled away, but usually there is dry and scaly hair loss. The lesions tend not to be itchy.
Hair re-growth starts in the centre of the lesion and active disease extends outwards. In some horses, the hair coat merely looks rough with broken hairs and only small areas of hair loss.
Often more than one horse is affected and also other animals (dogs, cats) or humans may develop skin lesions.
Secondary bacterial infection can result in a purulent discharge and more painful lesions.
How will my veterinarian confirm my horse has ringworm?
Your veterinarian will need to know the complete history of the problem and will carry out a physical examination of your horse. Ringworm lesions can look similar to rain scald (dermatophilosis), sarcoids or skin rubs.
Hair samples and skin scrapings from the edge of the lesion will be taken to perform a microscopic examination to look for the presence of dermatophyte fungi.
A sample may be cultured to identify the fungal species involved (this can take up to 30 days) or a PCR test may be used for the detection of dermatophytes.
Your veterinarian may choose to perform a skin biopsy to confirm fungal infection.
Can my horse be treated for ringworm?
The disease is usually self-limiting in immunocompetent animals and it requires 1-4 months to resolve.
Treatment is generally recommended to reduce duration, severity and limit spreading to other subjects. Gloves and overalls should be worn when dealing with infected horses and hands washed thoroughly afterwards.
Anti-fungal topical shampoos, rinses and creams can be used to treat the horse. All lesions and surrounding areas, and ideally all the hair coat, should be treated, at least 2-3 times weekly and continued for 2-4 weeks after resolution of the clinical signs.
Any potentially contaminated areas, such as stabling, should be thoroughly disinfected. All rugs, tack and grooming equipment should also be washed in fungicidal disinfectant.
Re-infection is possible for horses previously exposed.
How can I prevent my horse from developing ringworm?
Fungal spores can survive for long periods in the stable and there is no specific prevention for ringworm. New arrivals should be quarantined prior to admittance onto the main yard. Tack, rugs and brushes, etc should not be shared between horses. Good horse and stable hygiene and well-fitting clean tack can help limit the risk of infection.
Isolation of infected animals reduces the risk of spread to other horses. Wearing gloves, protective clothing and washing hands is good practice when handling and treating infected horses.