Rain scald
Rain scald is caused by the bacteria dermatophilus congolensis which lives in the soil and can infect damaged skin. This damage can be caused by wounds and grazes or continual wetting of the skin, hence it being most commonly seen in wet and muddy conditions.
Signs
The signs of rain scald are matting of the hair and scab formation on the back and rump.
Diagnosis
The characteristic signs of rain scald are usually enough for a diagnosis to be made, however, the bacteria can be grown in a lab from a sample of the affected area.
Treatment
The initial treatment in rain scald cases is to remove the horse from pasture if this is possible. Then the affected areas should be thoroughly washed with an antiseptic solution such as hibiscrub or pevidine and all the scabs removed. In some cases the area may need to clipped to achieve this adequately. An antibiotic cream should be applied to the areas twice a day. Your vet will prescribe you a cream for this purpose, I tend to use Flamazine cream or Fuciderm. This treatment should be carried out until the scabs have completely healed.
Prevention
The best method of treating mud fever is to prevent it from happening in the first place. To do this rugging horses up when on pasture can be very helpful, although, the bacteria can still occasionally infect the area. As soon as any small scabs start appearing the horse should be brought in from the field and the area cleaned of any mud and allowed to dry.