Rain Rot or Scald (Dermatophilosis) in Horses

D. congolensis is commonly believed to live in the soil and has been found on the skin of animals and people. Risk factors for developing rain rot include:

• Horses with compromised immune systems
• Malnourished horses
• Chronic exposure to moisture

Veterinary attention is warranted for horses with symptoms of rain rot. Prompt treatment and environmental management helps prevent the condition from worsening. Left untreated, ongoing skin infection and pain can decrease overall quality of life, especially in vulnerable horses. Dermatophilosis infections can spread rapidly if not caught and treated early.

Rain rot is common in horses. Dermatophilosis can occur in horses of all ages, but is most commonly seen in young horses or immunocompromised older horses that are continually exposed to moisture.

Most infections subside in 2-3 weeks and heal without scar formation. In more serious cases, scabs and crusts can spread, particularly along the back, and horses often lose weight due to pain while moving. Severely infected horses may require euthanasia.

The scabs or crusts from dermatophilosis can be painful, particularly when touched. Horses that have extensive infection of the lower limbs may experience lameness or swelling of the legs. In some cases, rain rot may be associated with hair loss.

Horses with severe infections where tack sits may resent riding or saddling.

Dermatophilosis in horses is caused by the bacteria Dermatophilus congolensis.

Excess moisture compromises the natural barrier that the outer layer of the skin provides, making it susceptible to bacterial invasion. Exposure to insect bites, particularly flies and ticks, can also increase a horse’s risk of becoming infected.

Diagnosis of rain rot is usually presumptive based on the appearance, location, and size of the scabs or crusts noted during physical examination. A definitive diagnosis is made by microscopic examination, scabs or lesions are sampled for laboratory examination.

Treatment involves targeting the bacterial infection, including treatments such as:

• Gently soaking and removing the scabs
• Applying betadine or chlorhexidine antibacterial agents to the skin underneath removed crusts
• Antibacterial shampoos
• Antibiotics
• Clipping the coat

Removed scabs must be properly disposed of to prevent the bacteria from contaminating the environment and spreading to other animals.

Horses also require management changes to prevent rain rot from reoccurring. Management strategies include:

• Regular grooming and bathing
• Reducing exposure to environmental factors such as excessive moisture (ie. rain or humidity) through providing shelter, stabling, or blanketing
• Feeding a balanced diet

Most dermatophilosis infections heal within 2-3 weeks and wounds heal without scarring. Horses that are continuously exposed to environmental risk factors may develop rain rot again.

Horses with severe infections often lose condition, and movement is painful if the feet or legs are severely affected. Severely infected horses may have to be euthanized.

Reducing environmental risk factors and practicing good hygiene, with regular grooming and bathing, can prevent a horse from getting rain rot.

Dermatophilosis can be transmitted to other animals and people. Infected horses should be isolated from other animals to reduce spread of the disease. Infected horses should be handled with gloves, and thorough handwashing with antibacterial soap is recommended after contact with an infected horse. Transmission can also be minimized by disinfecting tack, grooming supplies, blankets, and other accessories and by not sharing equipment between horses.

Dermatophilosis is common in horses.

• Antibacterial baths and ointment
• Antibiotics
• Clipping coat
• Soaking, removing, disposing of scabs
• Environmental management