Papillomavirus Part 1: Wart Worries
From Guest Author Dr. Angelika Schoster, Department of Clinical Studies, University of Guelph.
Papillomaviruses (PVs) are small DNA-based viruses that are recognized causes of disease in many animal species and humans. More than 100 different human papillomavirus types (HPV) have been identified, which can cause a range of problems from annoying (but benign) warts to malignant cervical cancer. The ability of papillomaviruses to cause cancer was first recognized in animals, specifically with cottontail rabbit papillomavirus (CRPV), bovine papillomavirus (BPV) and canine oral papillomavirus (COPV). In general, PV infection causes benign disease in the vast majority of individuals, but the viruses have the potential to cause malignant disease in a small proportion of the mammals they infect as well.
Horses can be infected by both equine papillomavirus (EPV) and some bovine papillomaviruses. Infection with BPV is associated with equine sarcoids – look for more information on BPV in horses in an upcoming post. Infection with EPV (specifically Equuus caballus papillomavirus types I and II) causes cutaneous papillomas – small proliferative skin lesions better known as warts. Warts are benign growths that appear on animals less than two years of age. They typically persist for 6-12 months and then disappear without any specific treatment, and they do not otherwise make the animal sick. Usually warts appear on the muzzle and lips, but rarely genital warts can occur (usually with infection by the type II virus). Occasionally warts can also occur on the lower limbs, ears and eyelids.
Warts can be spread between horses by fomites (e.g. objects, equipment, tack, clothing that has been contaminated with EPV), or by close horse-to-horse contact. Spread is common when young are horses are brought together in large groups for shows, sales or breeding. Infection is usually diagnosed by the characteristic skin lesions, the horse’s history and age - more than 90% of affected horses are less than three years old. Usually the warts regress spontaneously and they do not require treatment. However, if treatment is sought for esthetic reasons, cryosurgery (i.e. freezing, usually with something like liquid nitrogen) can be performed. Caustic chemicals such as trifluoracetic acid can also be used to “burn” the warts off. Even after treatment, though, the warts can recur.
Controlling warts caused by EPV is fairly simple: if you have an affected horse, keep it away from other young horses. Do not allow the horses to have direct contact, and make sure the horse with the warts has its own tack, grooming supplies, water bucket, hay net/trough etc. so the virus is not indirectly transmitted to others. There is no vaccine available for horses for EPV. There are a lot of “voodo” treatments for warts out there, and some people swear by them, but (just like people who treat foal heat diarrhea) that’s usually because they’re treating a condition which goes away on its own anyway. People cannot be infected by EPV.
Photo: Warts on the nose and lips of a horse (source: http://www.yourveterinaryclinic.com)
