Coital Exanthema is a disease that causes ulcerated lesions on and around a horse's genitalia. The virus can effect both male and female horses. There is currently no known cure for the STD, but supportive care to keep the horse comfortable during an outbreak may include antibiotics to treat secondary infection, antiseptic wash, and/or topical creams.
It is important to contact a licensed veterinarian immediately, and to isolate the effected horse(s) to prevent further spread of the Coital Exanthema.
The typical outbreak, from the first signs to the lesions being fully healed, lasts about three weeks. It is important not to allow the horse to engage in sexual activity during this time, as this is when the virus is able to spread. When there are no signs/ symptoms of Coital Exanthema, horses are generally able to breed successfully. (The disease generally does not cause sterility.)
It is also possible for the virus to spread from unsanitary veterinary practices. Be sure your veterinarian sterilizes all tools and surfaces before and after treating or examining your horse.