Disorders of the Outer Ear in Horses
A variety of skin conditions affect the outside part of the ear, called the pinna. Most conditions cause tissue changes elsewhere as well. Rarely, a disease affects the outer ear alone. As with all skin conditions, a diagnosis is based on a thorough history, a complete physical and skin examination, and carefully selected diagnostic tests.
Insects and parasites commonly cause inflammation of the pinna in horses—-resulting in redness, swelling, itching, small bumps, scabs, or blistering—either through direct damage from the bite of the parasite or as a result of hypersensitivity (an allergic reaction).
Ticks can cause irritation at the site of attachment and may be found on the pinna or in the ear canal. The ear tick, found in the southwestern United States, South and Central America, southern Africa, and India, is a soft-shelled tick whose younger, immature forms infest and live on the external ear canal of horses. Signs of infestation include head shaking, head rubbing, or drooped ears. Both the animal and the environment (pasture and stable) should be treated. Your veterinarian can recommend the most appropriate treatment for your horse. The spinous ear tick (Otobius megnini) is found in the southwestern United States, south and central Americas, southern Africa, and India. Immature ticks (larvae and nymphs) feed within the ear canal of horses and other animals. Signs include head shaking, head rubbing, or drooping ears. Treatment involves removing as many ticks as possible with a forceps and the use of topical insecticides. Any secondary bacterial or yeast infections must also be treated. The environment should also be treated to help prevent future infestations.
Nonburrowing psoroptic mites cause an itchy, inflamed ear canal in horses. Some horses show no signs of infection, whereas others may shake their heads and have a drooping ear. Bumps with scabs, hair loss, and/or scaly skin are common. Diagnosis is confirmed by finding the mites on skin scrapings or in ear discharges, but mites may be difficult to find in the ear canal. Medications are available for controlling these conditions. Your veterinarian will prescribe the one that is most appropriate for your horse.
Sarcoptes scabiei is a different species of mites that more commonly affects dogs and pigs but also rarely infects horses. Sarcoptic mange causes severe itching and skin changes (such as small bumps; scabs; hair loss; or thickened, leathery skin) on the ear and other parts of the body. If the infestation is not treated, the disease may extend over the whole body, leading to severe weight loss, general weakness, and unwillingness to eat. The diagnosis is based on signs, history, and the discovery of the mite within skin scrapings. However, the mites can be difficult to find, so multiple scrapes or a biopsy may be necessary. Your veterinarian will prescribe a medication to eliminate the mites. Because mites can survive off of the host animal, all bedding, brushes, and tack should be treated as well. Your veterinarian may also recommend that other animals in contact with an infected horse be treated for this contagious mite.
Fly strike (irritation of the ears caused by biting flies) is a worldwide problem in horses caused by stable flies, black flies, and biting midges (Culicoides species). The fly bite causes small, hard, round bumps and raised, reddened areas with central bloody crusts that itch. Tissue changes are found on the tips of the ears. In horses, the fly bites can cause a hypersensitivity reaction or severe inflammation of the skin, resulting in tissue changes on the hind and/or lower part of the body and face in addition to the outer ear. Treatment includes fly repellents, controlling the fly population with environmental cleanup (for example, removing manure), and insecticides.
Equine aural plaques are raised, pinkish bumps and patches on the inner surface of the ear. They are caused by a papillomavirus that is likely transmitted by black flies. These flies are active at dawn and dusk, when they attack the head, ears, and lower abdomen of horses. The thickened, hard, round bumps and patches eventually grow together. Often, both ears are affected. The plaques do not usually cause signs, but in some cases the direct effect of the fly bite causes skin inflammation and discomfort. Treatment includes frequent applications of fly repellent and stabling the horse during the hours when black flies are active. The plaques typically do not go away.
Frostbite may occur in animals poorly adapted to cold climates and is more likely in wet or windy conditions. It typically affects body regions that are not well insulated, including the tips of the ears. The skin may be pale or red, swollen, and painful. In severe cases, death to tissue and shedding of the ear tips may follow. Treatment consists of rapid, gentle warming and supportive care. Amputation of affected regions may be required but is usually delayed until the extent of living tissue is determined.
Several immune-mediated diseases may affect the outer ear and ear canal. Other areas of the body are typically affected and may include mucous membranes or skin. Immune-mediated diseases are confirmed with a biopsy of the abnormal tissue.
Also see professional content regarding diseases of the pinna.