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 tissue. As the horse’s body responds, inflammation and immunity develop, which halts the infection from spreading throughout the entire body. [1]

However, this immune response process can take several weeks to fully stop the infection. Since ringworm is highly contagious, it can spread during this time through close contact with other animals, grooming tools, and blankets. [2]

Climate influences the prevalence of ringworm in horses, affecting fungal growth and transmission. Warmer, humid climates create ideal conditions for the fungi to proliferate, increasing the risk of infection. [2][5]

Young horses kept in groups, as well as senior and immunocompromised horses, are more susceptible to ringworm due to compromised or undeveloped immune systems. [2][4][6]

New arrivals to a property are susceptible to ringworm due to potential exposure to fungal spores in the environment or on other animals, compounded by the stress of transportation and adjusting to a new environment. New arrivals also pose a risk to existing animals on the farm, as they may bring ringworm into the herd. [6]

An unclean environment increases the risk of ringworm transmission among horses because it provides ideal conditions for fungal growth and survival. Contaminated surfaces, poor hygiene practices, and close contact facilitates the spread of fungal spores, increasing the likelihood of infection. [5]

Other factors that may predispose horses to ringworm include: [8]

Diagnosis

Ringworm is typically diagnosed based on observation of characteristic signs, which include circular lesions accompanied by hair loss, crusting, and inflammation. Signs of infection are found on various parts of the body such as the trunk, limbs and neck. [3]

Skin and hair scrapings collected from affected areas may be examined under microscope in a laboratory to detect fungal spores. This method is the most accurate diagnostic technique, allowing for early detection to prevent the spread of ringworm among horses. [1]

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Culture

Culturing for ringworm involves taking hair and skin samples from the affected area on the horse’s body and placing them on a special culture medium in a lab. After a fixed incubation period, the culture is checked for dermatophyte fungi growth. If ringworm growth is observed, a diagnosis is confirmed. [4][6]

Although highly accurate, culturing can take up to 30 days. Other diagnostic methods are often sufficient, so many cases are diagnosed without this method. [4][6]

PCR Testing

Molecular PCR (Polymerase Chain Reaction) tests have been developed to identify the dermatophyte species responsible for ringworm infections in horses.

By targeting specific DNA sequences unique to these fungal pathogens, PCR tests can accurately and quickly detect and differentiate between dermatophyte species. [2][6][7][9]

Differential Diagnosis

When confirming a ringworm diagnosing in horses, it’s important to rule other possible causes of skin lesions.

The following conditions produce symptoms similar to ringworm in horses: [4]

Treatment

In healthy horses with robust immune systems, ringworm is often self-limiting. This means the body’s immune response is sufficient to resolve the infection over time, with some horses experiencing sudden, complete remission within three months. [2]

However, recovery duration varies; mild cases may clear up within a few weeks, while more severe or widespread infections may take several months to fully resolve. [4]

Infected horses must be isolated to prevent the spread of ringworm to other horses, humans, and animals on the property.

Quarantining affected horses allows for focused treatment and management strategies, minimizing the overall impact of the infection on the herd or stable.

Sanitation

Effective treatment for ringworm also requires thorough cleaning of the horse’s environment to reduce the risk of reinfection.

Disinfect any surfaces or equipment the horse may have contacted during the infection, including:

  • Stall walls and flooring
  • Tack and equipment
  • Feed troughs and water buckets
  • Brushes
  • Trailers

Dispose of bedding and other materials that cannot be thoroughly disinfected.

Avoid direct contact with infected horses to prevent spreading the fungal spores. Handlers should wear personal protective equipment (PPE), such as gloves and disposable boot covers when caring for horses with ringworm. [4]

Topical Medication

Topical antifungal medications, such as shampoos, creams, or sprays containing miconazole or chlorhexidine, can be applied directly to the affected areas to combat the fungal infection and promote healing.

For optimal effectiveness, treat the entire hair coat to ensure thorough coverage without missing any areas. Treatment should be applied at least 2-3 times per week, following the specific instructions provided by your veterinarian. [4][7]

Topical treatments for ringworm may not always be effective due to inadequate coverage and the challenge of consistent application. Additionally, if the horse continues to come into contact with contaminated environments or objects, reinfection can occur.

Systemic Medication

In some cases, your veterinarian may prescribe your horse oral antifungal medications to provide full-body (systemic) treatment.

The medication and dosage used depends on how severe the infection is and the horse’s response to treatment. Oral treatment is typically reserved for severe or widespread ringworm infections or when topical therapy alone isn’t effective.

Griseofulvin is an antifungal medication commonly prescribed to treat ringworm in horses. It is administered orally and works by preventing the fungi from growing and reproducing, ultimately eliminating the infection from the horse’s system. [7][10]

Horses with liver problems should not be given griseofulvin, as this drug is processed in the liver. Horses with impaired liver function may experience drug accumulation in the bloodstream, leading to potential toxicity. Additionally, griseofulvin may worsen liver dysfunction or cause further damage. [7][10]

Always consult a veterinarian before administering new medication to your horse. Inform your veterinarian of any other medications your horse is on when discussing treatment.

 

Prevention

Proper biosecurity protocols are key to preventing ringworm in horse populations. Implementing the following measures can help reduce the risk of infection: [2][4]

  • Maintain a clean environment: Keep stables, pastures, and grooming areas clean and well-maintained. Regularly remove manure, soiled bedding, and debris to help minimize fungal spore contamination.
  • Quarantine new and infected horses: New horses should be isolated for a number of days or weeks before introducing them to the herd to prevent the spread of ringworm and other contagious diseases. Monitor them closely for signs of infection during quarantine.
  • Avoid overcrowding: Avoid excessive direct contact between horses to prevent transmission. Separate infected horses from healthy ones until the infection resolves.
  • Practice good hygiene: Wear gloves and wash hands thoroughly with soap and water after handling infected horses or contaminated equipment. Use separate grooming tools and equipment for infected horses to prevent cross-contamination.
  • Disinfect equipment: Regularly clean and disinfect grooming tools, tack, and equipment using products that are effective against fungal spores. Avoid sharing tack, blankets, and grooming tools between horses to prevent transmission.
  • Educate handlers and barn staff: Ensure that anyone who handles horses at your equine facility is aware of the symptoms of ringworm and the importance of biosecurity measures to prevent its spread.

Nutrition

Horses with nutritional deficiencies in their diet are more susceptible to health problems, including skin infections. Feeding a balanced diet is key to supporting a horse’s immune system so it can defend against fungal infections, such as ringworm.

Important nutrients for supporting skin health and immune function include:

  • Vitamin A: Essential for maintaining a healthy immune system to protect against infections. Ensure your horse’s diet includes sufficient vitamin A from sources like fresh pasture grass.
  • Vitamin E and Selenium: Both act as antioxidants, protecting cells from damage and supporting the immune system. Horses consuming hay and those living in central North America likely require supplementation in one or both nutrients.
  • Zinc: An important trace mineral that is commonly deficient in the equine diet. Zinc deficiency can impair wound healing, immune function and skin and coat quality.
  • Copper: Plays a role in the formation of collagen, an important protein in the skin. Adequate copper levels help maintain skin strength and resilience.
  • Amino Acids: High-quality protein sources provide essential amino acids like lysine and methionine, which are important for tissue repair and immune function.
  • Omega-3 Fatty Acids: These essential fatty acids, including EPA and DHA, support skin health, wound healing and normal homeostatic regulation of inflammation. Feeding a fat supplement enriched with omega-3’s also gives your horse a healthy, shiny coat.

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Prognosis

The prognosis for ringworm in horses is generally good, as it is not a life-threatening condition. With timely diagnosis and appropriate treatment, ringworm can be effectively managed and resolved.

Treatment success largely depends on factors such as the severity of the infection, the horse’s overall health, and the chosen treatment approach.

Despite treatment, some horses may experience persistent or recurrent ringworm infections. This can be due to various factors, including incomplete eradication of fungal spores, a compromised immune system, or reinfection from contact with contaminated surfaces or animals. [4]

Summary

Ringworm is a highly contagious fungal skin infection caused by dermatophytes, a group of fungi that invade the skin and hair to feed on keratin.

  • Clinical signs of ringworm include circular patches of hair loss with crusty, scaly skin, resulting in discomfort and itchiness
  • Treatment includes topical antifungal medications, environmental management, and sometimes oral antifungal medication
  • Proper management is essential to prevent spread to other horses and humans; prevention measures include hygiene practices and isolation of infected horses

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References

  1. Merchant, S. R. Ringworm (Dermatophytosis) in Horses – Horse Owners. 2019.
  2. Ahdy, A. M. et al. Prevalence and Potential Risk Factors of Dermatophytosis in Arabian Horses in Egypt. Journal of Equine Veterinary Science. 2016.
  3. Maurice, M. N. et al. Equine Dermatophytosis: A Survey of Its Occurrence and Species Distribution among Horses in Kaduna State, Nigeria. Scientifica (Cairo). 2016.View Summary
  4. Funiciello, B. and Conwell, R. Ringworm – a fungal infection in Horses (Equis). Vet Lexicon.
  5. Al-Ani, F. K. et al. Ringworm Infection of Cattle and Horses in Jordan. Acta Vet. Brno. 2002.
  6. Durham, A. Diagnosing and Treating Ringworm in Horses. In Practice. 2020.
  7. Young, A. Ringworm in Horses (Dermatophytosis). UC Davis School of Veterinary Medicine. 2022.
  8. Hamad, M. et al. Clinical And Laboratory Studies On Equine Dermatophytosis. Benha Veterinary Medical Journal. 2019.
  9. Łagowski, D. et al. Real-Time PCR as an Alternative Technique for Detection of Dermatophytes in Cattle Herds. Animals (Basel). 2021.
  10. Mercer, M. A. Griseofulvin for Use in Animals – Pharmacology.Merck. 2022