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External Ear Infection (External Otitis) in Dogs

External otitis is an infection of the ear canal. The ear canals are delicate structures and are easily infected. Eighty percent of infections occur in breeds with long, dropped ears. This is a function of lack of air circulation; open, erect ears dry out more easily than dropped ears and therefore provide less favorable conditions for bacterial growth.

Many factors contribute to the development of external otitis. Some breeds (such as the Chinese Shar-Pei) are predisposed because of narrow or stenotic ear canals. Other breeds may be predisposed because they have an abundance of hair that blocks the circulation of air. Many dogs with allergic skin diseases, particularly canine atopy and food hypersensitivity dermatitis, are predisposed to ear infections as part of the generalized skin response. Similarly, dogs with primary and secondary seborrhea often have ear canal involvement characterized by a buildup of yellowish oily wax that provides an excellent medium for bacterial growth. Foreign bodies such as grass seeds and foxtails, and growths in the ear canal, are other predisposing causes. Ear mites can precede bacterial otitis.

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Iatrogenic causes of infection include using cotton-tipped applicators to clean the deep recesses of the ears, allowing water to get into the ears during bathing, excessive and improper cleaning of the ears, and a grooming routine that calls for plucking or clipping hair in the external ear canals.

Signs of external otitis are head-shaking and scratching and rubbing at the affected ear. The ear is painful. The dog often tilts or carries her head down on the painful side and cries or whines when the ear is touched. An examination reveals redness and swelling of the skin folds. There usually is a waxy or purulent discharge with a bad odor. Hearing can be affected.

Ceruminous otitis occurs with primary seborrhea. There is an extensive buildup of oily, yellowish wax in the ear canals, which provides an excellent medium for bacteria and yeast. Treatment is directed toward control of the seborrhea. Regularly cleaning the ear canal may be necessary until this problem is controlled.

Bacterial otitis, in its acute form, is usually caused by Staphylococci. The discharge is moist and light brown. Chronic infections usually are caused by Proteus or Pseudomonas bacteria. The discharge is generally yellow or green, although there are exceptions. More than one species of bacteria may be involved, which complicates antibiotic treatment.

Yeast or fungal infections may follow antibiotic treatment of bacterial otitis. Yeast infections also occur commonly in dogs suffering from atopic dermatitis, food hypersensitive dermatitis, and seborrheic skin diseases. A brown, waxy discharge with a rancid odor is sometimes seen, or a very red, inflamed, moist ear with minimal discharge. These infections tend to persist until the underlying disease is controlled.

WebMD Veterinary Reference from "Dog Owner's Home Veterinary Handbook"

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