The Dermatophilus organism itself is very susceptible to penicillin, so your veterinarian may prescribe that for severe cases. Blankets shouldn't be used between horses, but if they are, they should be washed and disinfected before being used on another horse. Also, if the horse you're treating is blanketed, make sure to wash his blanket to prevent re-infection. It's important to disinfect anything you use on an infected horse before using it on another horse-halters, saddle pads, brushes. Even if the horse has a favorite place he rubs, like a stall door or a fence, it can become a source of the organism.
Diagnosis is usually by clinical signs, and the disease can manifest itself in several ways.
It can result in rather large, crusty, circular areas. When it's like that, there will be a mass of raised hair all over the horse's back. In either case, there is a crust of serum that elevates the hair. As the disease progresses, the crust may increase to a quarter of an inch thick. The disease is not usually associated with any discomfort or itching except when you remove the scab, which is painful.