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Coital exanthema is a venereal disease that likely occurs throughout the world. Both genders of horses are affected as a result of the equine herpesvirus type 3 (EHV-3). The disease is not cancerous and though it is transmitted primarily through sexual intercourse, there have been outbreaks where the disease was transmitted through supplies, instruments, or even a glove used for a rectal exam that were contaminated; thus the disease can occur in horses even if they have not procreated. In some cases of coital exanthema, a secondary infection will develop which will also require treatment.
Caused by the equine herpesvirus type 3 (EHV-3), coital exanthema is a venereal disease that affects horses of both genders leading to lesions on or near the horse’s genitals.
Symptoms in mares will typically occur between 4-8 days after contact (sexual or with a contaminated instrument or supply) and will include a number of red nodules on the vulvar, vaginal mucosa, clitoral sinus and perineal skin. The diameter of the nodules may be up to 2 mm and they will develop into vesicles and pustules that will ultimately tear, leaving inflamed expanses that may grow together into bigger lesions. Swelling may occur in the perineum and possibly between the thighs as well. In some cases, ulcers will develop on the teats, lips, and nasal mucosa.
Streptococcus spp may lead to the development of a secondary bacterial infection in the ulcers. The infection will lead the ulcers to grow and give off a discharge of mucus and pus and some horses run a fever.
Stallions will experience similar lesions to those found in mares. The lesions will occur on the penis and the prepuce. The lesions will cause sexual intercourse to be painful, which may lead the stallion to be hesitant to participate. Should the horse copulate when his condition is ulcerative, the viability of his sperm may decrease as a result of the ulcers hemorrhaging in the ejaculate. The stallion may also appear depressed and be uninterested in eating.
There are eight types of herpes viruses noted in horses, with three of them considered to cause disease. These viruses are named equine herpes virus or EHV 1-8. In addition to EHV-3, equine herpes viruses 1 and 4 are associated with disease in horses.
Coital exanthema is caused by the equine herpesvirus type 3 (EHV-3). Typically, the EHV-3 is transmitted through sexual intercourse, though it is also possible for the disease to be transmitted through supplies, instruments or even a glove that had been used for a rectal exam and became contaminated. It is thought that the disease is only spread in the acute phase. Once lesions are healed, it seems that the horse will no longer shed the virus. It is not clear whether the horse will continue to be a carrier of the disease. It is thought that immunity to the disease does not last long, though evidence points to it being unlikely for a horse to develop the disease more than once within a breeding season.
Your veterinarian will conduct a full physical examination of your horse and ask you for information regarding what symptoms you have seen in your horse, when you first noticed them and what changes you have seen. If your veterinarian is not familiar with your horse’s history, he may ask you for that information to determine if it is possible that your horse was exposed to the equine herpesvirus type 3. After the physical examination, your veterinarian can make a tentative diagnosis of coital exanthema. In order to confirm the diagnosis, your veterinarian may look at the virus in the cells from the ulcers under an electron microscope. Another option would be to look for intranuclear herpesvirus inclusion bodies in cytologic or histologic preparations.
Coital exanthema is a self-limiting condition. Treatment for the condition will require that the horse abstain from sex for three weeks. Until the ulcers heal the disease can continue to be spread through sexual contact. Should your horse have a secondary bacterial infection in addition to coital exanthema, your veterinarian may recommend an antibiotic ointment to help with treatment.
With no secondary bacterial infection, your horse’s skin should be completely healed within three weeks, though ulcers on the clitoris and vagina will take more time to heal. The ulcers will appear as scars without pigment for a long period after healing. After infection, the virus can be shed for 40 days.
Should your horse have developed coital exanthema, it is important that you follow the recommendations of your veterinarian and attend follow up appointments as scheduled in order to assure the best outcome for your horse.
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