Of the 70,000+ species of fungi that scientists have identified, about 50 of these can potentially cause infections (mycoses) in animals and humans. Of the several classes of disease-causing fungi, the superficial and cutaneous types can infect the skin of horses.1 

• Superficial fungi affect the skin alone.

• Cutaneous fungi attack the skin as well, but can also affect the hair. 

Fungal skin infections in the horse are categorized as dermatophytosis and dermatomycosis. 

• Dermatophytosis involves infection of the keratinized tissues including the hair and are usually caused by fungi such as Microsporum, Trichophyton or Epidermophyton. 

• Dermatomycoses are fungal infections of the hair, hoof or skin, and are caused by non-dermatophyte fungi.2 

Ringworm is one of the most common fungal skin infections affecting horses. It is usually caused by a dermatophyte fungus (e.g., Microsporum or Trichophyton) and presents with skin lesions which start as small raised spots from which the hair is lost.3 Over time, the lesions can spread from these spots and become thick and scabrous.1 Occasionally, the lesions can be sore and itchy. Only two or three lesions may be seen, but if left untreated, the condition can become extensive. Ringworm is highly contagious and can be spread to humans. Entire groups of horses have become infected during outbreaks, often through the process of systematic grooming in a facility.

Occurrence and Diagnosis

In most cases, ringworm is transmitted from horse to horse by direct contact, tack, grooming equipment or contact with facilities where the fungi are present. The fungi that cause ringworm are highly resistant to environmental factors and can remain on viable on surfaces for long periods of time. They can remain on a horse’s skin for up to 21 days before clinical signs develop; this means that the condition can be spread well before signs of infection develop. Very often, a new horse will introduce ringworm to a facility.3 It is thought that younger horses are more susceptible than older ones, although geriatric or debilitated animals are also considered to be more at risk as well. More often than not, horses that have been infected develop a strong immunity and are usually not subsequently infected, even if exposed.1,3

Ringworm lesions are usually characteristic as described above, but can resemble other skin conditions like rain scald or folliculitis. A veterinarian can confirm diagnosis by collecting skin scrapings and subsequent analysis of skin cells, debris and hair for ringworm spores. Since ringworm spores take several weeks to culture however,  veterinarians usually recommend treatment prior to confirmation.

Ringworm cases can spontaneously resolve within 6 to 12 weeks3 however, given the high risk of spreading ringworm within a facility, treatment is the more prudent option. Additionally, horses with active cases of ringworm are prohibited from competing or racing and are unable to travel abroad. It therefore makes more sense to treat cases as soon as they arise.

Where to buy Griseofulvin 

Griseofulvin is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

Griseofulvin carries several potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1wagwalking.com.

2Padalino, B. et. al. Rare Generalized Form of Fungal Dermatitis in a Horse: Case Report. Animals: an open access journal from MDPI vol. 10,5 871. 17 May. 2020.

3vcahospitals.com.