Ringworm is a fungal infection in horses that causes skin irritation and is highly contagious. The fungi can be transmitted through direct contact with an infected horse or indirectly through contaminated grooming tools, tack or bedding.

Affected horses often develop girth itch, characterized by circular patches of hair loss and crusty, scaly lesions that form where the girth rubs against the skin. [1]

Ringworm can affect horses of all ages, although younger horses and those with compromised immune systems are more susceptible. Horses kept in close quarters, such as in stables or at shows, are at higher risk.

Treating ringworm typically involves antifungal medications, environmental decontamination and isolation of horses to prevent the spread of the infection. Keep reading to learn more about how ringworm spreads and what you can do to prevent it in your herd.

Ringworm in Horses

Ringworm, or dermatophytosis, is a common fungal skin infection in horses and other mammals.

Despite its name, ringworm isn’t caused by a worm but rather by dermatophyte fungi that that feed on keratin, a protein found in the outer layer of the skin, hair, and nails.

In horses, the most common dermatophytes responsible for ringworm are Trichophyton equinum and Microsporum gypseum.

Although ringworm isn’t life-threatening, it is highly contagious and can spread through contact with horses, equipment or the environment. It can also be spread to humans and other animals. [2]

Ringworm is referred to by several other names, including girth itch and stable itch. The term “girth itch” refers to lesions around the girth and armpit. If the girth rubs the skin and causes sores, fungi can infect and thrive in this humid area.

Quarantining infected horses and preventing them from participating in shows, races, and other events is crucial to reduce the risk of spread to other horses. [3]

Transmission

Horses can contract ringworm through both direct and indirect routes. The fungi causing ringworm thrive in the soil and on rodents, surviving for extended periods in warm and humid conditions. [1][2][3][7]

Horses can become infected when they dig, roll, or lie in contaminated areas, coming into contact with fungal spores. These spores settle in the horse’s coat and mature into microscopic fungi that inhabit the hair follicles and feed on keratin in the outer layer of skin and hair.

Ringworm is also highly contagious through direct contact with horses and other animals, including humans. Its contagious nature is partly due to its long incubation period of 2-3 weeks. During this time, infected horses may not show visible signs of infection but can shed fungal spores into the environment. [4][6]

Infected horses shed spores through activities like grooming, rolling, or rubbing against surfaces. This disperses fungal spores into the environment where other animals may encounter them. Horses in close contact are highly susceptible to contracting ringworm from each other.

Additionally, ringworm fungi can survive on surfaces, soil, and organic matter like bedding or grooming tools. This resilience enables them to persist in the environment, increasing the likelihood of transmission to other animals.

Symptoms

Ringworm presents with distinct clinical signs that help with its identification and diagnosis in horses.

The following common signs are typically observed: [1][4][5][6]

  • Circular lesions: A hallmark sign of ringworm is the presence of circular lesions on the horse’s skin. These lesions often appear as raised, scaly patches with a defined border, resembling rings. They typically develop where the horse’s skin rubs against tack and other equipment, such as the girth area, face, lower legs, neck, and flanks. This is why ringworm is often referred to as “girth itch.”
  • Hair loss: Affected areas commonly exhibit hair loss within the circular lesions. As the infection progresses, the hair surrounding the lesion may become brittle or break off, worsening the appearance of hair loss.
  • Irritation: The horse’s skin may be sensitive, mildly painful or itchy. Some horses show signs of discomfort, such as rubbing, scratching, or biting at the affected areas. If left untreated, rubbing can worsen skin damage and contribute to the spread of the infection.
  • Crusting and scaling: Ringworm lesions may develop small pustules or crusts, particularly if the infection becomes further infected with bacteria.

Most cases involve localized lesions that can appear anywhere on the body except the mane and tail. [6]

Widespread ringworm infections across the body are rare in horses. When generalized infection does occur, it usually affects vulnerable individuals, such as horses with compromised immune systems or foals with developing immune systems.

Risk Factors

Pre-existing skin damage increases the risk of ringworm infection in horses. Minor abrasions or cuts provide an entry point for fungal spores to invade the outer layer of skin and target the hair follicles. [4]

Dermatophytes primarily grow in dead skin and hair cells, stopping when they reach living cells or inflamed tis