Rain Scald

Cause

Rain scald, sometimes referred to as rain rot or mud fever, is a skin condition seen in horses. It is caused by the bacteria Dermatophilus congolensis. For the bacteria to take hold and cause an infection there needs to be a break in the skin and moisture. Prolonged periods of the horses coat being wet, either from rain or through daily washing/exercise without thoroughly drying out, combined with hot and humid weather are the ideal conditions for the bacteria to thrive in.

Spread

The bacteria that causes rain scald can be spread from an infected horse to another horse through biting and non-biting insects. It can also be spread by sharing brushes, rugs and tack that have been used on an infected horse. It can develop in any horse however it is more common in younger or older horses or those with a compromised immune system.

Symptoms and Diagnosis

Rain scald develops when the bacteria enters through a break in the skin, even a small cut, scratch or bite. The bacteria causes infection in the skin which then discharges a yellow-greenish pus. The pus causes matted hair and hair loss that tends to come out in tufts. The skin lesions can also become crusty, swollen, hot and are often sensitive or painful. It is typically seen in places where water may sit or not drain easily like the back, rump, head, neck and wither. The appearance of rain scald is quite distinctive and a veterinarian can usually diagnosis it just by looking at it. If required (although not typical) smears and swabs can be taken for confirmation.

Treatment

Treatment of rain scald typically involves washing the horse with an anti-bacterial wash, usually containing iodine or chlorhexidine. The horse needs to be washed daily for a week, then twice a week until healed, allowing the wash to sit on the coat for at least ten minutes before rinsing off. If the infection is bad enough a veterinarian may prescribe antibiotics.

Prevention

To prevent rain scald it is essential to keep your horse dry. Keeping them in stables or rugged with a waterproof rug during rain periods is ideal. Also ensure after exercise or when bathing that the horse is able to thoroughly dry off.

Originally published in My Pet Magazine Summer 2018/19.

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