A product has been shown to be effective in the treatment of specific ear lesions, called aural plaques, in horses.
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. They 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.
Many treatments have been used for aural plaques, but none is considered reliably effective.
Now, researchers at the University of Minnesota suggest imiquimod, marketed as Aldara, can help clear 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 effectiveness of 5%-strength 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, including some skin cancers.
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 re-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 six weeks to eight 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 $US250.
The horses did not become more head-shy after treatment, despite the inflammatory response and their annoyance at having the crusts and debris clear away before re-applications.
"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!"
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