With the onset of mud and rain, one of the other more common conditions that we run across is the infection of the skin that goes by a number of different names: Rain Scald, Rain Rot, Scratches, Dew Poisoning, Skin Funk, Greasy Heel, or Dermatophilosis. In reality, these conditions do represent slightly different infections with different agents or bacteria but they all can have similar clinical signs and treating the cases can be the same. This condition can affect horses, cattle, sheep, goats, dogs, cats, and even be transferred to people.
Dermatophilosis specifically is an infection by the bacteria Dermatophilus congolensis. However, when an animal becomes infected, frequently there are multiple organisms that can be isolated after a very short period of time and a generalized bacterial dermatitis results. Given the right environment, sometimes a fungus may cause an additional infection and create a condition called Dermatophytosis. This can be confusing, but since treatment tends to be similar for all of these, we usually just go straight to treatment.
Dermatophilosis is usually seen over the back, hindquarters, back of pasterns, or on the hind cannons. The disease is frequently worse over white skinned areas. Lesions can be small dry crusts that are easily removed with grooming or rubbing, or they can be larger crusts with yellow-green or gray colored pus underneath them. Early in the infection, removal of crusts or touching the horse in the affected area can cause pain. Hair attached to the crusts tends to fall out easily as the crusts are removed, producing the typical “paintbrush” look that characterizes this disease. Rain soaked skin, or skin that is broken, irritated, or damaged by insect bites or trauma is more likely to develop the disease.
Three things need to be present for the disease to manifest. First, the organism needs to be on the animal (dirty). Second, moisture (not a problem here in Oregon), and third…heat. The animal’s body heat actually is enough to make the infection take off, and with long hair trapped under blankets or standing in bedding can be enough to allow for the infection to take off.
Dermatophilosis is contagious and can spread to other animals and people by contact with the crusts or by shared tack and grooming kit. Treatment is usually aimed at removing the crusts gently (MTG works well) and washing the skin with an antiseptic shampoo such as iodine or chlorhexidine. Just as important, the animal must be rinsed very well as any scabs that are just rinsed to a lower part of the leg can re-infect. After bathing, a salve or cream can help reduce the sensitivity of the skin.
Antibiotics are frequently necessary to help control the infection if it gets deep enough in the skin. Sometimes anti-fungal medication is also used. Transmission between animals and people can be avoided by not sharing tack or grooming supplies, and disinfecting all equipment that comes into contact with infected horses. If you are uncertain, please call your vet to have them advise you as to the best course of action.