Equine papilloma virus can cause benign skin warts or sarcoids (tumours). The virus is closely related to the bovine papilloma virus. Though it is harmless in the bovine, the virus affects horses differently, causing temporary skin damage.
Equine Papilloma Virus
Equine papilloma virus (EPV) causes warts on a horse's skin. They are benign (non-cancerous) skin tumours that often affect horses younger than 3 years of age because the young horses haven't yet built a strong immunity. The lesions look like common warts and typically affect the lips and muzzle, though they may spread to the eyelids, genitals and lower legs. The virus is highly contagious to other horses, but they disappear within two to three months without scarring. If warts interfere with eating or detract from the hourse's appearance, the owner may have them surgically removed or frozen off (cryosurgery). Surgical removal, however, carries a risk of mild scarring. Topical treatments are available. Infected horses should be isolated to prevent transmissison of the virus and all contaminated equipment should be disinfected. Seek a veterinarian's advice for the best treatments as well as for recommendations for safe disinfectants.
EPV also causes ear papillomas (aural plaques). These lesions, which appear inside your horse's ears, are round, flat, white marks covered with a waxy film. They have a scaly appearance and are often called "ear fungus," though no fungus is present. Aural plaques typically affect horses 1 year of age and older. These lesions may also infect the anus and genitals. The growth rate of aural plaques is erratic. Sometimes only a few appear and do not spread; in other instances they cover the entire inner ear. Plaques do not resolve on their own like the EPV warts, yet they typically pose only a cosmetic concern. Some horses may develop severe head-shyness as a result of aural plaques. A head-shy horse is scared, jumpy or anxious, and may avoid being touched.
Black flies, which carry the virus from horse to horse, may also irritate existing plaques or make the skin susceptible to growth of plaques. Horses may become more sensitive during the summer, when fly bites are more likely to irritate aural plaques. Face masks, complete with screens and ear coverage, are recommended during summer months. Do not apply fly repellents directly to plaques; doing so may cause further irritation.
Ear Papillomas Treatment
There is no known guaranteed treatment or cure for aural plaques. Some horse owners use tretinoin (Retin-A) with success. Keep the inside of the ear clean, protect the ears from flies and leave the lesions alone to prevent further irritation. In the most severe cases, where the horse is in pain and severely head shy, a veterinarian may surgically remove the lesions with cryosurgery. The primary risk associated with cryosurgery is the formation of scar tissue.
Seek veterinary care to ensure the lesions are not sarcoids, which require different treatments. Aural plaques are usually smooth, flat and white. If the lesions are painful, grow rapidly, have an irregular surface, or have a non-white discolouration they may be sarcoids. A veterinarian must conduct tests for proper diagnosis.
Sarcoids look like warts, but they are caused by a different papilloma virus: bovine (cow) papilloma virus, or BPV. Sarcoids are not cancerous. Sarcoid growths usually appear around the ears, face genitals, between the front legs, and behind the elbows, but they may grow anywhere. Sarcoids grow deeper into the skin's surface and may be painful.
A biopsy is required to determine if a growth is a sarcoid. If so, a veterinarian may recommend surgical removal, cryosurgery or injections. Some topical medications may work effectively on sarcoids. If steps taken do not completely remove the tumour, new growths may appear. Depending on the type of sarcoid, treatments may include the Bacille Calmette-Guerin (BCG) vaccine, radiation therapy or chemotherapy. Some sarcoids will disappear within a few weeks to a few months. There is no evidence that sarcoids are contagious.