We have seen many cases of rain scald in the last couple of months with the increased moisture and humidity. Rain scald is caused by the bacteria Dermotophilus congolensis in horses.
If left untreated, it can be quite a painful and irritating condition for the horse. It causes a moist dermatitis, which appears as scabs and clumps of hair matted together.
When these scabs lift off, there is no hair or ‘alopecia’ underneath. The ‘rain scald’ part of the name derives from the fact that moisture such as rain on the lesions will track the bacteria elsewhere on the body. Thus it typically occurs over the back/dorsal midline.
Young and old horses are generally affected more frequently, but it can occur in horses of any age/breed/sex.
Thick hair coats may hide the scabs initially until the rain scald is quite advanced, and also acts to keep moisture around the lesions. ‘Rain scald’ is also a bit of a misnomer, as it frequently occurs in horses that are rugged and technically haven’t had any rain on them!
Treatment must involve removal of the scabs, as they act as a continued source of infection.
The horse should be washed thoroughly in an antibacterial such as chlorhexidine or iodine. Scabs should be removed with a brush or fingernails. Drying the affected areas is important, as moisture and humidity will enhance the spread of the bacteria.
A bit of sunlight will help too rather than a heavy rug that they might sweat under.
In most cases ‘rain scald’ is a relatively superficial infection that will clear up with topical antibacterials. Deep infections may however require systemic antibiotics such as penicillin. These would be very painful oozing sores. Don’t ignore the small scabs – early treatment is very effective.
Dr Sarah Cavill.