The virus known as papilloma affects just about every species of animal. It usually causes skin eruptions, and in people 100 different subtypes of the virus have been identified. In young women one type causes genital warts which usually disappear in time. Another type of the virus can cause the very serious problem of cervical cancer.
The horse’s head is a target for two equine types of the papilloma virus. One causes a mass of warty growths all around the muzzle in yearlings and youngsters up to about 3 years old. There are ointments that are designed to make them go away. Another treatment is to remove a few of the warts by cutting them at their base. The idea behind this is that when you snip them off, they bleed and some of the virus gets into the blood stream. The immune system then produces a response to make the rest disappear. I have tried both the ointments and the surgery, and my experience is that neither the ointments nor the snipping of the warts speeds up their disappearance. With time they always go away on their own. Muzzle warts don’t bother horses, but they can get in the way of their sale at an auction barn. They are most often seen in racing stock because the youngsters on brood farms are usually running together, and the virus is spread from one to another by nose contact. Because they are contagious, your vet may not be able to fill out a shipping health certificate for affected youngsters with warts. The interesting thing about them is that one day the muzzle will be peppered with warts, and a few months later, one day they are all gone.
The other common papilloma of the horse’s head causes a far more irritating problem called aural plaques. The word aural means ear, and the word plaque refers to its raised appearance. The virus causes a huge skin overgrowth on the inside of the ear. The mass may stick out a good ¾ of an inch above the level of the skin of the inside of the ear. It looks like a fungus growing out of the bark of a tree. Google “aural plaques horse” for typical photographs. The growths are pink or gray in color and the dead skin on the surface is continually flaking off. Insects are thought to spread this form of the virus which in northern New England means our friend the black fly.
It is tempting to want to scrub out the ear of a horse with aural plaques. I used to do that. They hate it, so my procedure was to tranquilize the affected horse quite heavily. I then used a damp gauze pad and diligently scrubbed out the messy plaques right down to the normal skin level. After that I applied the latest salve, and had the owner follow up doing the same. The problem was that often after this aggressive treatment the owners couldn’t get near those ears, sometimes for months afterwards. By the way, the plaques always came back.
The latest treatment being used for aural plaques is Aldera, which is an expensive human ointment, used to treat those papilloma genital warts in teenagers. One research study showed that it is effective for aural plaques, but the report also says that ointment itself can be irritating, and I’m not sure that the horses in the study wouldn’t have gotten better on their own.
Having dealt with many cases of both muzzle warts and aural plaques I am now convinced that both should just be left alone to heal. For each, nothing I’ve used so far seems to help either problem. While aural plaques are ugly, most horses are not bothered by them. However, if you aggressively scrape them out, the ears become painful and then horses become very sensitive to their ears being touched in any way. I have known a few horses that after ear cleaning would not even permit a bridle to be slipped over their ears. Instead the owners had to approach the horse with the bridle in pieces and put it on very carefully, piece by piece to avoid touching the ear. Most horses eventually get better, and while the lesions don’t totally disappear, they do subside with time and become less noticeable. Take the Beatle’s words of wisdom from the song and for aural plaques and muzzle warts, “let it be, let it be.”
Dr Jefferson is the founding veterinarian of Maine Equine Associates. He can be reached at www.MaineEquineAssociates.com His previous articles that have appeared in the The Horse’s Maine are archived on that site.