by Barry B. Burtis D.V.M.
Ear infections are one of the most commonly diagnosed disorders in the dog. They have been reported to affect 10 to 20 percent of the canine population. Many dogs suffer recurrent ear infections. In the cat, ear infections are much less common with incidence reported to be somewhere between 2 to 10 percent. There are several possible predisposing causes for an ear infection. Predisposing factors do not cause infection but increase the chance of its development.
The conformation of the ear canal is quite similar in cats and dogs. They have ear canals that have a long vertical canal and slightly shorter horizontal canal. This relatively much longer canal than in a human ear is often thought to be a factor in leading to inflammation and infections in this part of an ear.
Stenosis or narrowing of the ear canal is probably a risk factor for infection. Narrowing of the canal may be something an individual is born with or it might be the result of injury or previous infections. Stenosis will prevent good air circulation in that long ear canal. It will make cleaning the canal more difficult.
Excessive hair in the ear may predispose to problems. Hair follicles are present and hair grows in the ear canals of most dogs. There are considerable breed differences in the amount of hair. Hair follicles are much less numerous in the feline ear canal. In my opinion, hair by itself, is not a significant risk for an ear infection but, if other predisposing causes exist, it may become a factor.
Pendulous pinnae are listed as another possible predisposition to ear infections. Basset hounds lead the league in those kinds of ears. Personally, I have not found them over-represented in patients I have treated for ear infections. However, theory states that those long ears have more opportunity to get dirty, get wet, get into trouble, in general, and therefore be more prone to infections.
The lining of the external ear canal in both dogs and cats contains many sebaceous glands and fewer ceruminous (wax-producing) glands. Research has shown there can be significant breed differences in the density of the ceruminous glands. If more wax and sebum is produced and accumulates in the canal, it definitely becomes a better place for both yeast and bacterial infections to develop.
Increased moisture, in and around the ear canal has long been thought to be an important ingredient in any recipe to make an ear infection. High environmental humidity and/or temperature seems increase the threat of an ear infection. Swimming or poor technique in bathing allows a chance for water to get down into the ear canal. Even strenuous head shaking may not dislodge all the wet. If wax or other debris is in the canal it may be even more difficult for the canal to dry.
A healthy ear has a normal pH and conditions important in resisting infection. Anything that disrupts that environment can predispose to infection. Over treatment with antibiotics or other drugs may set up conditions favouring more troublesome bacteria or other organisms. This may significantly increase the risk of recurring problems.
Finally, any systemic disease, a disease affecting the body, in general, can lower resistance to ear problems. It will be very important to be on the lookout for problems in the ears. Treatment of a problem in this site may be critical in helping the patient.
Now, having reviewed possible predisposing causes, next time we'll look at some primary and perpetuating causes for ear infections. Barry Burtis is a local companion animal veterinarian. Past Pet Tales can be found at www.baycitiesanimalhospital.ca