Dr. Caity Cosentino
Have you ever looked insides a horse’s ears and seen white, flaky, rough-looking lesions and wondered what caused them? These plaques are caused by a papillomavirus, spread by the bites of black flies. Black flies tend to be most active at dusk and dawn and are drawn to a horse’s head, ears, and abdomen. The bites themselves can cause local irritation and dermatitis, but these flies can also spread several strains of papillomavirus, responsible for creating these lesions on the inner surface of a horse’s ear (as if we needed another reason to dislike flies!). Most of the time these lesions are of cosmetic concern only and are benign, not affecting the horse at all. There are times, however, that these lesions are painful and cause sensitivity to the ears creating behaviors like head tossing or head shyness when having a halter or bridle put on. If a horse is experiencing discomfort from the aural plaques, an owner may wish to pursue treatment for the lesions, which can be difficult to get rid of. There have been several treatments tried, with variable clinical responses, but no definitive treatment is available. Clipping the hair, removing the scabs and applying an ointment with a steroid in it may help decrease the size of the lesion and relieve the pain, but likely will not completely cure the area. Immunomodulatory therapy with a drug called Imiquimod cream has been successful in cases at eliminating the lesions. This therapy can be challenging to accomplish however, due to the extreme inflammatory reaction the cream causes at the aural plaque sites. Horses often become even more head shy and won’t allow for the cream to be applied and sedation may be required to follow the treatment protocol. Due to the fact that the treatment often causes more discomfort than the plaques themselves, monitoring instead of treatment is often the best option, unless the plaques do seem to be bothering the horse.
The best way to help prevent the occurrence and spread of aural plaques in horses, and among a herd, is fly protection, in the form of sprays, ointments, and fly masks with ears. Limiting the ears exposure to biting flies can both prevent the occurrence of aural plaques and decrease the size and irritation of plaques already present in a horse’s ears. If you notice your horse is developing a white plaque in it’s ear, it’s best to ramp up your fly protection before the lesion becomes a problem for your horse. Continued exposure to fly bites can irritate a plaque that was previously not causing any problems. Aural plaques do not usually regress on their own, but can be quiet and not bothersome to your equine friend, as long as you protect the area from those pesky flies. Even with treatment, these plaques are likely to recur at some point down the road due to the fact that the papillomavirus can become dormant in the horse’s body. It is important to get any lesion of concern examined by a veterinarian, as there are other conditions, such as sarcoids and sarcomas, that can resemble aural plaques, but are caused by different disease processes and require different treatments. Even though aural plaques are usually a cosmetic concern, it’s best to try to prevent their occurrence by using good fly protection while your horse is outside.