Rain scald is a condition generally found during autumn and winter months and is found on the skin of the horse, usually on the back and flanks. It is caused by a bacteria called Dermatophilus congolensis. Localised infection of the legs with Dermatophilus is referred to as mud fever.
It occurs most commonly in horses and ponies kept or exercised outdoors in wet and muddy conditions. If the affected area is under tack, then it may stop the horse from being ridden. It can be contagious and spreads from horse to horse, either by direct contact or via rugs, brushes and tack.
Rain scald can be identified as scabs, often with tufts of hair attached to them. These may be found on the back and flanks of the horse. The hair on the scabs may stand up and look like paintbrush bristles. The scabs may vary in size and if removed, there may be yellow pus on the skin underneath the scab. The scabs can be painful to the horse if removed, but are not usually itchy.
Long standing cases may have large areas of scabs which merge together, giving a plaque-like appearance on the skin. The coat will look very coarse and tufty on these areas. White skinned areas seem to be more susceptible to infection.
Mud fever is caused by similar infections of the legs. The horse may be lame, especially if the scabs are around the heels and coronet band. In severe cases, cellulitis may occur and the horse’s leg will swell.
A diagnosis of rain scald is made by identifying the scabs and sometimes your vet may take a swab or send off one or more of the removed scabs for culture, to try to grow the Dermatophilus bacteria.
If your horse or pony has been diagnosed with rain scald, it should be brought into a stable and kept dry. If this is not possible, a waterproof rug should be used. Cases of mud fever need to be removed from muddy fields and kept in a clean, dry stable if possible. It is very important to keep the skin dry.
The ‘paintbrush’ scabs should be gently removed and disposed of. Remember the scabs can spread infection of Dermatophilus. In severe cases, the coat may need clipped out. Again, remember to clean the clippers thoroughly to prevent spread to other horses.
Once you have removed as many scabs as possible, wash or spray the affected areas with either a chlorhexadine solution (diluted Hibiscrub) or povidone-iodine solution for 7 to 10 days. Dry the skin thoroughly after each wash and keep dry until the next application. Topical application of antibiotic cream may be useful but barrier cream should be avoided until the scabs have been removed as they can be difficult to wash off. It would be worthwhile washing items used for the grooming the affected horse in the same solution. Do not share items of tack or rugs with other horses to prevent spread.
In severe cases, your vet may prescribe antibiotics. Recovery from Rain Scald may take up to 3 weeks. A horse will not become immune to rain scald or mud fever. If your horse has had it once, it may suffer from it again in the future, especially in wet and muddy conditions.
• Rain Scald is avoidable with good management.
• It is caused by the bacteria Dermatophilus congolensis.
• The condition is contagious between horses either by direct contact or by sharing rugs, tack and brushes.
• It is usually straightforward to treat by keeping the horse dry and using anti-bacterial washes.
• If your horse has Rain Scald or Mud Fever once, it does not become immune and can suffer from it every winter.
• Rain scald may prevent you from riding your horse or pony as it will be uncomfortable underneath the saddle
•You may not be able to ride your horse for up to 3 weeks in severe cases
•Antibiotic may be prescribed by your vet in severe cases
•Your horse may become lame with mud fever
Sunny was kept out in the field without any shelter or a rug. His owner noticed patches all over his body which looked like sticky paintbrush bristles. His owner called the vet who diagnosed Rain Scald. Sunny was brought in from the field and kept in a dry stable. His owner removed the scabs and washed the underlying skin with dilute hibiscrub. Within a fortnight, these patches had vanished and Sunny was able to be ridden again.
© XLVet UK Ltd.