Rain Scald in Horses

By Deidre M. Carson, BVSc, MRCVS & Sidney W. Ricketts, LVO, BSc, BVSc, DESM, DipECEIM, FRCPath, FRCVS.

What is Rain Scald?

Rain scald is a bacterial infection of the skin that results in the formation of matted scabs usually affecting the back and rump but occasionally the lower limbs.

What causes Rain Scald?

rain_scald-1The bacteria that causes rain scald is called Dermatophilus congolensis.  Prolonged wetting and cracking of the skin surface, as occurs in wet weather, allows the bacteria to invade the surface layer of the skin and establish an infection.

What does Rain Scald look like?

In mild cases, the horse may just have a few flat scabs containing mats of hair. When the scabs are removed the underneath surface is slightly moist and sometimes raw. In severe cases the coat over the horse's back and rump will feel hard and painful and will consist of many scabs lying next to each other. If the scabs are gently removed, the horse may be left with a large area of bare, raw, skin (see photo).

When the infection affects the lower limbs it is called mud fever and similar scabby lesions will be found, particularly on the back of the pastern and fetlock and the limbs may become swollen. Rain scald may occasionally affect the face.

Is there anything else that looks like Rain Scald?

It is relatively easy to confuse cases of ringworm and some parasitic conditions of the skin with rain scald. Ringworm tends more to be associated with dry 'flaking' of the skin and when ringworm 'scabs' lift off, the skin underneath tends to be dry and scaly, although this is not always the case. In some cases of ringworm, the first signs are just patchy hair loss. Ringworm tends to occur anywhere on the body but particularly the face, neck, and limbs. Please see our handout on ringworm.

rain_scald-2These conditions can be differentiated by taking a skin scraping or hair pluck and looking for the causal fungi or bacteria under a microscope, in the laboratory.

How is Rain Scald treated?

Affected areas should be gently washed with a mild disinfectant shampoo or solution e.g., chlorhexidine or povidone iodine and as many of the scabs as possible removed without causing excessive discomfort to the horse. The skin should be dried or allowed to dry completely and a broad-spectrum antibiotic powder, spray or ointment applied. Gradually removing the scabs over several days, applying an antibiotic preparation and keeping the horse dry will result in resolution of the condition. If the horse has to go outside and the skin is continuing to become wet, it should be waterproofed by the application of a greasy or oily preparation such as zinc and castor oil, Vaseline or an antibiotic ointment. Severely affected horses may need systemic antibiotic treatment, i.e. by injection or by mouth.

Can Rain Scald be prevented?

As the bacteria multiplies best in warm, wet conditions, keeping the horse stabled, sheltered, or rugged with a waterproof rug during wet weather, protects the skin from prolonged wetting and helps to prevent infection.

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