A common condition of horses, especially younger animals. Older horses can be re-infected, but the signs are usually milder. Transmission can be facilitated by overcrowding, sub-optimal nutrition, or general poor sanitation. It can occur in places on the horse that are susceptible to microtrauma and exposure to tack, such as the saddle, girth, halter, bridle etc. It is passed on by direct contact with affected horses, both symptomatic and asymptomatic animals, from the environment, and commonly through fomites, such as brushes and tack.
Common organisms include the genera Trichophyton and Microsporum. These include the species Trichophyton equinum var. autotrophicum, Trichophyton equinum var. equinum, Trichophyton metagrophytes, Trichophyton verrucosum, Microsporum gypseum, and Microsporum canis.
Signs of Ringworm
Most horses develop patchy areas of scaling and hair loss, first appearing within 9 to 15 days of exposure. There may or may not be concurrent inflammation and crusting. This is dependent on the cause and the animal’s immune response. They may also be itching, although this is very inconsistent, and if present is usually in the earliest stage of the disease.
Diagnosis and Treatment
The ideal approach is through culture and fungus identification. A tip for culture is to add 1-2 drops of a soluble B vitamin complex (specifically Niacin), as some of the more common species will not grow without it. Other methods to diagnose ringworm include potassium hydroxide (KOH 10-20% concentration) or chlorphenolac preps of plucked hairs. Biopsy and wood’s lamp can also be used, although the lamp is only useful with some Microsporum strains (M. canis and M. equinum).
Many vets would treat for ringworm on the basis of clinical signs without pursuing a definitive diagnosis.
Clip the affected areas with wide margins to remove infected hairs. It is important to dispose of the hairs and to disinfect the clipper blades after use. Gently bathe the entire horse with 2% chlorhexidine and 2% miconazole shampoo (Malaseb Medicated shampoo by dermcare). Then apply 2% Lime sulphur or 0.2% Enilconazole (Imaverol) or topical ketoconazole (Nizoral or Ketochlor shampoo) to the entire animal. Be careful of lime sulphur, although reasonably effective, does have a bad odour and may stain horses with light coloured coats. Imaverol should be used every 3 days for 4 treatments.
Healing tends to begin at the centre, with the outside regions being the youngest and most active area of infection. The disease should be in remission within 3 months with topical therapy. Systemic therapy is not recommended.
It is important to sanitize the environment, including brushes, tack, and stables. You can use either 5% Lime sulphur, 5% formalin, 3% captan, 0.2% enilconazole or 5% sodium hypochlorite.
Ringworm is potential zoonosis. It is possible for humans to get infected so washing with an antifungal soap, protective clothing, and wearing gloves is important.
Tags: Infectious diseases; Dermatology; Zoonoses