Rain scald, also called rain rot or “dermatophilosis”, is an infection of the skin, caused by the bacteria Dermatophilus congolensis.
Dermatophilus is an oppertunistic bacteria. It’s a regular occupant of the horse's skin, but lies dormant and doesn’t cause any harm under normal circum stances. When the skin becomes compromised, the bacteria seices its opportunity to invade, causing an infection.
What can cause the skin to become compromised?
When the skin becomes wet/moist for prolonged periods, it’s natural barrier may start to fail. Normally, when it rains, only the top layer of the horse's haircoat will get wet and the water runs off the horse's back without penetrating through the hair coat towards the skin. If rain continues, or the horse has a bad haircoat that has lost its natural repellent function, the skin may become wet as well.
If the horse dries up again shortly after, the skin can cope. However, when outside temperatures are low and the air is moist (wintertime), horses often won’t dry properly.
Horses that have dirt on their skin may be more prone: the dirt can harbour more than usual amounts of the bacteria.
Rain scald can also occur when a horse is rugged while being wet or sweaty from exrecise. The rug can seal in the moist keeping the skin wet and warm, which is the ideal environment for bacteria to brew in. (Fleece rugs are excellent rugs to use on wet horses that have shelter, because they allow moisture to come through/exit and therefore help the horse dry up.)
Dermatophilosis / rain scald presents as scabs on the skin, most often over the back area. Lesions begin as weepy sores, which become crusty, and in severe cases can become swollen and contain yellow-green pus. The rain scald lesions don’t itch, but the skin underneath the scabs is sensitive.
Diagnosis of rain scald is usually based on clinical findings. If in doubt, the pus underneath the scabs can be swabbed and sent to the lab to rule out other bacterial causes.
Treatment should be instigated as soon as possible, before the infection spreads. Treatment for rain scald is twofold:
- The area needs to be washed with an antibacterial wash, such as iodine or chlorhexidine. Carefully remove the scabs, which harbour the bacteria. Washes should be repeated daily until the skin has healed, because as we’ve explained before the bacteria occurs everywhere and will migrate back into the cleaned area if given the opportunity.
- The skin should be allowed to heal and regain its natural defense mechanism while the bacteria is being addressed. This means that the horse needs to be kept dry and clean. Because the affected area is usually washed repeatedly, it is important that the horse dries up properly again. Keep the horse out of the rain, or dry it up properly before rugging it.
Sometimes topical creams may be required as well.
The bacteria spreads to things that the horse touches, so the horse's rugs, brushes and other equipment should be washed/disinfected as well, and should not be sheared with other horses. Scabs are infectious so the should be disposed of properly.
Do you have any questions about rain scald or your horse? Give us a call and we’ll be happy to answer any of your questions.