Otitis Externa

As in human beings, the skin disorders are widespread in dogs. Dogs are especially susceptible to dermatoses. Among dermatoses in dogs, ear infection is one of the major constraints causing discomfort to the animal. An inflammatory condition of skin regardless of the cause is described as "Dermatitis". Skin and ear affections are most common clinical manifestations among dogs, though not usually fatal, these are aesthetically disagreeable to the owner and cause discomfort both to the dog and the owner. Ear infection (otitis) is an inflammation of the epithelial lining of the external auditory canal which is the portion of the external ear located between the pinna (ear flap) and the tympanic membrane.

The external ear is considered to be a specialized region and its infection (otitis) is thus considered as one of the skin diseases. The external ear canal of the dog is long and narrow and halfway along its length it turns from a vertical to a horizontal direction. The ear canal is lined by squamous epithelium which contains sebaceous and modified apocrine glands (the ceruminous glands). The ceruminous glands secrete a white, odourless fluid. Along with desquamated epithelial cell, these secretions combine to form cerumen.

Canine cerumen has been reported to enhance the growth of an yeast Malassezia pachydermatis, an organism frequently found resident on the ear skin. Besides, the normal microflora of skin is a mixture of resident and transient organisms which live in symbiosis. Bacteria and yeast are found in small numbers in normal ears of dogs and cats.

Bacteria commonly found in normal canine ears include Staphylococcus epidermidis, Staphylococcus intermedius, Micrococcus spp. and occasionally coliforms. Malassezia pachydermatis yeast commonly inhabit the oral cavity, lip commissures, external ear canals, interdigital webs, perineum and anal sacs. These yeasts belong to the normal cutaneous microflora but may behave as opportunistic pathogens whenever alterations in the microclimate of skin occur. It can be dangerous to immunocompromised humans.

Otitis is very common in dogs and causes a lot of distress and discomfort to the affected animals. Otitis externa has been traditionally described using terms such as reactive, inflammatory, and allergic or infectious.

Causes of Otitis

Primary factors are those that are capable of initiating inflammation in otherwise normal ears which include:

• Parasites
• Foreign bodies
• Hypersensitivity disorders
• Keratinization disorders
• Auto-immune skin disease
• Glandular disorders
• Viral diseases
• Miscellaneous conditions

Perpetuating factors are those that are responsible for continuing the inflammatory response even though the original primary factors may no longer be present or active:

• Bacteria
• Yeasts
• Otitis media
• Progressive pathologic changes in the ear canal

Predisposing Factors of Otitis

Conformation of the Ear Canal

The ear type is an important factor in determining an animal's risk of developing otitis externa. Faulty ear conformation has been considered to be the most important etiological factor in dogs. The pendulous pinnae of many breeds of dog restrict free circulation of air within the ear canal and may inhibit the radiation and convection of heat from the external ear canal.

Stenosis or swelling of the opening of the external ear canal is a real problem in some breeds, e.g. Pug, Chow Chow, English bulldog and Chinese Shar-Pei which suffer from otitis. The lack of a significant opening into the canal may reduce air circulation in the external canal.

Dense hairs found within the external auditory meatus of some breeds, such as the Poodles and Maltese terriers, impair ventilation and clearance of normal secretions.

Environment

Dogs when swim frequently or get wet by bathing, it stimulates activity of the ceruminous glands thus obstructing the ear canal with secretions and eventually favouring microbial proliferation.

Climate

The micro- environment of the ear canal becomes more suitable for bacterial and yeast growth with any alteration in the environmental heat and humidity.

Treatment Factors

Traumatic use of cotton-tipped applicators for removing exudates from the ear canal and vigorous plucking of hairs from the meatus, necessary or unnecessary, can lead to swelling and erosions of the otic epithelium, predisposing it to opportunistic infections. The overuse of certain otic cleansing solutions and strong antiseptics causes maceration of the ear canal (Bass, 2004). Improper use of topical antimicrobial preparations causes colonization of the ear canal with opportunistic gram-negative bacteria, such as Pseudomonas aeruginosa or Proteus mirabilis.

Anal Sac Disease

The correction of anal sac disease and recurrent otitis externa in dogs.

Main Causes of Otitis Externa

Parasites

A number of parasites such as Otodectes cyanotes, Demodex canis, Sarcoptes scabiei, Notoedres cati, ticks (e.g. Otobius megnini, the spinous ear tick of dogs), flies (e.g. Stomoxys calcitrans) and fleas (e.g. Echidnophaga gallinacea) have been associated with otitis externa.

Hypersensitivity Disorders

The hypersensitivity disorders such as atopy, food allergy and contact-allergic dermatitis, have been commonly associated with otitis in dogs.

Signs of Otitis Externa

The clinical signs include inflammation, increased discharge (with or without odor), and pawing at the ear.

Treatment of Otitis Externa

Treatment The prime target of therapy of otitis externa aims at elimination of the underlying cause, cleaning the ear canals and middle ear, applying topical therapies and administering systemic medication. A number of antibacterials have been suggested for use and have been found to be effective in the treatment of otitis externa and these include gentamicin, sulphadiazine in combination with trimethoprim, ampicillin, ampicillin in combination with cloxacillin, enrofloxacin, amoxycillin, cephalexin and cefadroxil.

Treatment regimen for fungal ear infections includes ketoconazole, and miconazole both topically as well as orally. However, despite the advancement in the therapeutic approaches, otitis externa can be resistant to antifungal antibiotics. Emergence of drug resistance is an important contributing factor. In view of these facts, herbal ear preparations may be of therapeutic efficacy in the treatment of otitis externa in dogs.

Apart from antimicrobials, ear infection require treatment for associated itichiness and other inflammation related signs using steroidal drugs like prednisolone, dexamethasone and non-steroidal anti-inflammatory drugs (NSAIDs) like clemastine fumarate, diphenhydramine hydrochloride, pheniramine maleate et cetera.

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