Veterinary Corner 10/01: Warts & Aural Plaques
by Frosty Franklin, DVM
Edgecliff Equine Hospital
S. 1322 Park Road, Spokane, WA 99212 * 509/924-6069Equine papillomavirus is the virus that causes the development of benign, proliferative skin tumors in horses. Microscopic evidence indicates that two different clinical presentations occur in the equine from the papillomavirus: (1) warts, and (2) aural plaques.
Equine warts are small, gray to pink cauliflower-like growths that are usually found of the muzzle, around the lips, nostrils, and eyes and occasionally on the lower legs. Warts can also involve the penis and vulva. Lesions commonly develop on young horses, 6 months to 3 years of age. The lesions range in size from 5mm to 20mm and are generally multiple in numbers. Ten to more than 100 warts are common. The incubation period is about 60 days. The warts reach maturity in 4 to 8 weeks. Then usually spontaneously regress within 4 months. Some cases may last more than a year. Cases that last more than 2 years may suggest an immune response deficit.
Warts are contagious. Transmission occurs by direct contact (nose to nose) and indirectly via fomites like fence posts and feed buckets. The virus remains vial in the environment for up to 3 weeks at room temperature. Yearly infection of young stock on large breeding farms has been reported. Lesions on the penis and vulva can result in transmission of the virus by breeding. Affected individuals should be kept away from the breeding herd. Disinfection of the premises and equipment with lye, formaldehyde, iodine, and chlorhexidine helps decrease spread of the virus.
Diagnosis is usually based on the clinical signs, history, and appearance. A large wart on the lower leg might be confused with a sarcoid. If the diagnosis is in question, a biopsy specimen may be collected and submitted for histologic diagnosis.
Usually treatment is unnecessary. The warts are harmless and almost always regress spontaneously. Management practices to limit the spread of the virus include insecticides, isolation of infected individuals, and disinfection of feed troughs, water buckets, and stalls.
Under certain conditions treatment is desirable. For instance, when a large mass of warts are interfering with biting or other tack causing a delay in training. Surgical excision and freezing with liquid nitrogen (cryosurgery) are often recommended. Various topical ointments have shown some success, however, compounds need to be very carefully applied and the horse prevented from licking and chewing the treated area. EqStim (immunostimulant) given intravenously has had reported success in both prevention and treatment of equine warts. Any treatment of warts that creates an inflammatory response may increase the risk of white hair and skin depigmentation.
Aural plaques are clinically recognized as different from warts. They are benign, raised, white to pink lesions that occur bilaterally on the inner surface of the ear. They respond poorly to treatment and do not spontaneously regress. They were thought to be caused by biting flies and are sometimes incorrectly described as "ear fungus". Infrequently, these plaques appear on the anus, penis and vulva. Aural plaques can be found on any horse older than one year of age. These plaques can become severely irritated by biting flies and horses become very defensive about having their ears touched.
Treatment with a soothing ointment, like Mentholatum, to the inner surface of the ear can be helpful. I have also tried the various corticosteroid/antibiotic ointments like Panalog or Otomax with a success. These ointments will relieve the inflammation but the plaques remain. I am not aware of a consistent treatment reported for aural plaques.
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