Ringworms in Horses: Signs & Symptoms

White horse run forward in dust on dark background

Ringworm is a common infection that derives its name from the characteristic bullseye rash that it creates on human skin. However, contrary to its name, ringworm is not a worm but a fungal infection. Likewise, it may not form like a circular ring on horses’ coats and manes.

Ringworm is the most common skin infection amongst horses. Because it spreads rapidly, horse owners should learn to recognize the signs and symptoms and get acquainted with the methods for treatment and prevention.

In this short guide, we’ll go over the basics of ringworms in horses.

Ringworm Symptoms

“Ringworm” is the vernacular name for a fungal infection called dermatophytosis.1 

This form of dermatitis (skin irritation) is most often caused by one of two different genera (families) of fungi:

  • Trichophyton – Worldwide, one specific species of fungi—Trichophyton rubrum—is the most common cause of ringworm infection, but other forms like Trichophyton violaceum can also cause infection.2
  • Microsporum – Fungi like Microsporum audouinii are less common causes of ringworm but may affect horses who travel internationally.

Ringworm affects the skin and the hair follicle but does not penetrate the skin to affect other bodily systems. To that end, ringworm is easily transmitted, but its signs and symptoms take between two and three weeks to appear.1

  • Because the fungus affects the hair, one of the first possible signs is the change in hair shaft angle. Small areas between 5-20 mm of hair may start to stick up against the grain of the coat (often in circular patches).
  • As the fungus acts on the hair’s keratin fibers, you may start to observe dusty or ashy-appearing particles in the coat.
  • Eventually, as hair continues to degrade, horses can develop bald patches with scaly surfaces.
  • As the skin heals, hair may start to reappear in the center of the patch first, creating a bullseye appearance.
  • Microsporum fungi produce smaller lesions. However, a smattering of lesions may appear like a large, non-circular bald patch.
  • Trichophyton fungi produce larger circular lesions with more hair loss that lead to bald sticky patches.

While ringworm is not life-threatening and clears up on its own over time, you should still take the infection seriously.

  • The affected areas are uncomfortable and irritating to your horse.
  • Open wounds elevate the risk of secondary infection by bacteria and other fungi.
  • Your horse will not be welcome at shows and races until the infection has been cleared.
  • Horses cannot travel with ringworms.
  • Ringworm can be spread to humans, cats, dogs, and other animals in the vicinity.3

Next, we’ll take a closer look at why this fungal infection is so common amongst horses.

How Ringworm Spreads

Like other fungi, the genera that produce ringworm infections spread via microscopic spores. 

To become infected with ringworm, a spore must make contact with a skin lesion. However, your horse doesn’t need a serious wound susceptible to infection. A minor abrasion or skin infection could open the gate for ringworm.

The chances of getting ringworm also depend on your environment. Fungi thrive in moist, humid environments. Once spores have fallen, they can thrive on all of the following surfaces:

  • Body brushes and grooming equipment
  • Communal wash buckets 
  • Bedding in stables and trailers
  • Timber
  • Clothing

Therefore, horses are at the most significant risk if they live in humid areas close to other animals. In these cases, the infection often appears in the saddle area (since horses may share tacks, saddles, and other equipment).

But ringworm can appear anywhere in the body and can affect horses in any environment.

Fungal spores are resilient to the cold, so ringworm infections can also occur in colder climates. For example, placing a contaminated blanket over your horse in winter may transfer ringworm from the hospitable surface of the bedding to your horse’s dense coat.

Once a single animal has a ringworm, it puts its neighbors at risk. While cases of horse-to-human transmission are pretty rare, ringworm can spread to any susceptible animal. 

Some Horses are More Affected by Ringworm

Brushing thoroughbred bay mare after wash in horse yards

As we’ve noted, ringworm is not usually life-threatening. Likewise, many adult horses have acquired some natural immunity to ringworm. After your horse has fought off a fungal ringworm infection, they develop a strong immunity to the fungus that can last for some time:4

  • Young horses who have never had a ringworm infection before are most susceptible to the disease.
  • A pregnant horse should not come in contact with ringworm to not complicate the pregnancy. 
  • Older horses with compromised immune systems can also become reinfected.
  • Your stable is at the highest risk when you introduce a new animal to others. Likewise, horses may come into contact with ringworms at races and shows.

Nonetheless, it’s essential to take action when a single animal is infected with ringworm. Otherwise, the infection can quickly spread.

Diagnosing Ringworm in Horses

Consult with a veterinarian at the first sign of changes in hair growth, flaking skin, or bald patches. Although the symptoms of ringworm are relatively distinctive, your vet will perform tests to confirm the diagnosis and rule out other conditions like bacterial staph and dermatophilus congolensis infections that may require a different course of treatment.

Potential diagnostic tools include:

  • Hair plucking – Ringworm affects the hair follicles. Therefore, you or a veterinarian can analyze hair from the surrounding area to detect fungi. 
  • Skin scrapings – Alternately, skin samples can be taken from active lesions.

Exposure to a 10% potassium hydroxide solution can quickly reveal whether a fungus is present.

If more information is needed, the fungus can also be cultured. This takes 30 days and helps to identify the particular species of fungus present. However, it does not affect the approach to treatment.

Once the cause of your horse’s dermatitis is confirmed, your veterinarian will advise a course of action.

Managing Ringworm

Most ringworm infections clear up on their own within 5-10 weeks. But if one of your horses has ringworm, you’ll want to take immediate action to prevent it from spreading to other animals (including yourself)!

Treating Your Horse

The first goal is managing discomfort and limiting the ability of the fungus to produce other spores. You’ll need to isolate any known affected animals and cease sharing equipment like brushes, bridles, and tacks.

Use the following principles to treat the affected animals:

  • Broken hair shafts and scabbing skin carry a high number of spores. Therefore, damaged tissue should be removed with a debriding agent like Dermisol or manually removed with tools like a toothbrush and nylon scouring pad.6
  • Consult with your veterinarian, who can prescribe an appropriate antifungal topical treatment. Typical choices include natamycin (Mycophyte), enilconazole (Imaverol), and miconazole.
  • Some vets may recommend additional oral or topical medication to help tackle fungus and avoid secondary infection in open skin wounds.
  • Wear gloves while interacting with your horse to avoid spreading spores. Likewise, wash your clothes and shoe soles before visiting other animals in the stable.

Observe your horse’s progress and continue consulting with your veterinarian until the hair has fully regrown.

Cleaning the Environment

Besides treating your horse, it’s of paramount importance to remove as many fungal spores as possible from the environment. As you know, from cleaning your kitchen and bathroom surfaces, fungi are incredibly tenacious. It’s near-impossible to sterilize an outdoor barn or stable completely.

But the more you can do to reduce the fungal population, the better. In which case, consider taking the following steps:

  • Wash and rinse all tacks and communal areas with antifungal solutions
  • Repeat treatment weekly to prevent new spores

Confirming the End of an Infection

If you’re hoping to bring your horse to a show or travel internationally, you may need proof that your horse is free of ringworm. In this case, call your vet for another hair sample or skin scraping. A clean sample can confirm that the infection is gone.

Best Methods for Preventing Ringworm