Aural plaques are whitish lesions on the inner surface of the ear. They are slightly raised, with a scaly appearance. One or both ears may be affected.
They are thought to be caused by infection with a papilloma (wart) virus and may be spread by biting flies. Aural plaques do not go away on their own and respond poorly to treatment.
Some affected horses resent having their ears touched and may become head-shy and difficult to bridle. However many horses are not concerned with the plaques, and the lesions seem to cause the owner more problems than the horse.
What can you do if your horse appears to be bothered by his aural plaques? Many treatments have been used for aural plaques, but none is reliably effective.
But now research at the University of Minnesota suggests imiquimod (Aldara™*) can help clear the aural plaques and make the ears less sensitive.
Dr Erin Malone and Dr Sheila Torres of the University’s College of Veterinary Medicine have been studying the value of 5% imiquimod cream to treat aural plaques. Their results were presented recently at the North American Veterinary Dermatology Forum.
Imiquimod is licensed for human use to treat warts caused by papilloma virus. It is also used to treat certain skin diseases -such as some skin cancers (e.g. squamous cell carcinoma.)
Exactly how it works is not known. But it is known to increase cytokine production, and also activates natural killer cells, macrophages and B-lympohcytes.
Although the cream itself does not appear to sting, it produces a strong inflammatory response. Ears become sensitive during treatment. Horses often resent the crusts and debris being cleared away, which is necessary each time before the cream is applied. It helps to clip the hair inside the ear before starting treatment. Horses often need to be sedated or twitched.
Sixteen horses completed the study. Imiquimod was applied three times a week on alternate weeks. If both ears were affected, only one of them was treated.
The lesions resolved completely in all horses, after being treated for between 6 weeks to 8 months. The lesions recurred in two horses during a follow up period of at least 12 months.
Treatment is quite expensive. Enough Aldara™ for a two month course of treatment costs about $250.
Is it worth it? You might think that horses would be more head-shy after treatment. Apparently not. “Those horses that were irritated by their ears prior to treatment actually seem improved (less head shy, less ear sensitive, easier to bridle) than they were before” Dr Malone reports. “Luckily they seem to forgive us!”
For more details see:
The efficacy of imiquimod (Aldara ™) in the treatment of equine aural plaque: an open-label pilot study.
SM Torres et al. Presentation at the North American Veterinary Dermatology Forum. Savannah Georgia. April 2009. Proc NAVDF (2009) p240.
(*Aldara™, 3M, St Paul, MN, USA)