Equine Aural Plaques in Horses

Aural plaques in horses are uncomfortable looking viral infections that affect the ears. This variety of papillomavirus is transmitted by insects, usually a type of black fly, and it causes tiny warts and thickening of the skin. Unlike papillomaviruses that attack the face of the horse and then fade, warts and lesions of the aural version of do not spontaneously resolve. Aural plaques that are not distressing to the horse may be left untreated, but if pain and discomfort are involved, medications that stimulate a localized inflammatory response can help the horse’s own immune system to heal the infections.

Equine aural plaques are patches of raised white papules or lesions in the ear. They are also referred to as papillary acanthomas, pineal dermatitis, or ear papillomas.

Aural plaques that are found in horses may or may not be painful, although the bites from the flies that transmit the virus may cause both pain and itching. Other symptoms that may indicate an infection on the ear by the papilloma virus can include:

• Discoloration
• Drooping ears
• Head shaking
• Lesions
• Shiny reddened skin undergrowths
• Sudden head or halter shyness
• Whitish, flaky growth

Types

Although black flies are the usual vector for aural plaques caused by the papillomavirus, other disorders caused by insects can mimic the signs. Some of these parasitic disorders include:

Culicoides

These are a type of small, aggressive gnat that attacks horses at the ears, belly, and the bases of the mane and tail. The bites of these gnats, known as buffalo gnats or humpies, are known to be highly allergenic for equines and can cause severe itching that can lead to dangerous infections if left untreated. 

Mites

Psoroptic mites feed superficially on the surface of the skin.The most common psoroptic mites to affect horses and livestock include psoroptes cuniculi, psoroptes equi, and psoroptes ovis.

Otobius megnini

Also known as the spinose ear tick, this soft-bodied tick can be found in the ears of horses, cattle, sheep, goats, and dogs. They usually infest the ear in large groups and can cause ulceration of the inner ear, blood loss, and even deafness.

Equine aural plaques are caused by an infection of the papillomavirus in the ear. This particular virus is spread to horses through the bites of flies. It is believed that the flies most responsible for spreading this particular variety of papillomavirus are a species of simulium fly, more commonly known as black flies.

Aural plaques are similar in appearance to many other disorders including infections by mites, molluscum contagiosum, and some tumors. They can occur in either one or both ears and do not spontaneously regress like the variety of papilloma virus that is responsible for warts around the face. The examining veterinarian will most likely take a sample of the affected skin to examine it microscopically. Regular microscopes will be able to use this to rule out conditions like mites and other parasites, however, an electron microscope may be able to identify the viral particles, which should be hexagonal.

The biopsied tissue will also be evaluated to rule out cancers and other types of tumors, and tests will be run to determine which virus is responsible for the by uncovering which antibodies can be found in the lesions themselves. While performing the ear exam, your horse’s doctor will pay close attention to the patient’s reactions to the handling of the ears, taking  his comfort level into consideration before creating a treatment plan.

Some aural plaques do not cause any pain or discomfort to the horse and are therefore left untreated. In these cases, it is important to monitor the plaques to ensure that they do not contract secondary infections and to take measures to reduce additional fly bites. Many veterinary practices use a prescription drug called imiquimod in a 5% solution directly on the ear for horses that are uncomfortable. In most cases, the animal will need to be sedated, particularly the first time the solution is administered.

The ear of the horse is shaved and all the crusting removed prior to administration of the medication. Subsequent applications are usually simpler and can often be handled by the owner. These treatments are generally several times a week every other week for at least two months and the ointment may cause additional swelling, redness, and even oozing that may seem alarming and has lead many owners to quit treatment early if they are unaware of the side-effects.

Horses with untreated aural plaques may be targeted by insects in the spring and summer months, and controlling the insects in their area is crucial to preventing escalation. Some of the steps you can take to reduce the number of insects in your barns and pastures include:

• As much as possible, limit evening and night time turn out in the field and paddock
• As birds and bats are predators of flying insects, install a bird or bat house near the stable or in proximity to lakes or ponds
• Use low lighting at night
• Empty all buckets and clean water troughs regularly, as well as other standing water, and ensure that damp vegetation is also removed from around the barn and paddocks
• Spray the stable area with a safe insecticide
• Use a fly maks to protect the eyes and ears, particularly in warmer weather