Mud fever (or scratches) is not a single disease but can be seen in differing forms. It occurs especially in warm, wet weather, and is associated with a number of causes.  Mud fever can range from a mild skin irritation to very painful infected sores, and can in some cases cause significant swelling with severe lameness. The condition affects the lower limb, most commonly the back of the pastern. It starts off as matted hair with little dry crusts. When the same condition occurs on the upper body it is referred to as “rain scald or rain rot”. The bacterias Dermatophilus congolensis causes mud fever and under normal circumstances those bacterias lives in soil as spores and can survive from year to year. These spores become activated by wet weather and this is why we see the disease when the ground is wet. Keeping an healthy skin on your horse is  key for protection. In the winter the rain, wet snow and mud soften the skin, constant wetting and drying of the legs causes the skin in this area to chap, and then the bacteria can enter.  However, anything which breaks the skin such as a small cut or wound can allow the bacteria to enter the skin. For this reason muddy conditions are not always necessary for mud fever to occur. ​ Some horses seem more prone than others and this is because their skin is a less efficient barrier to infection. For example, horses with white and/or hairless pasterns appear to suffer more and horses with very hairy legs may suffer less (as their skin is a bit more protected). The diagnosis of mud fever is usually straight forward and can be made by identifying the matted hair, crusty scabs and exudate on a horse’s leg.  The importance of regular inspection of the horse’s legs to catch the condition early cannot be stressed enough, and as always, prevention is much better than cure.