Otitis Externa (Ear Infections)

Otis Externa is the technical name for inflammation of the external ear and is infection of the external ear canal (outer ear) by bacteria or yeast. It is one of the most common types of infections seen in dogs. Some breeds, particularly those with floppy or hairy ears like Cocker Spaniels, Miniature Poodles or Old English Sheepdogs, seem more prone to ear infections, but they can occur in any breed and owning a cocker does not automatically mean you will have a dog plagued with ear infections.

Good ear health (regardless of breed) is all about good ear management! Any dog with dirty and hair filled ear canals will be prone to ear infections.

Signs & Symptoms

A cocker spaniel with an ear infection is uncomfortable & the ear canals are sensitive to touch. The dog will shake its head and scratch its ears trying to get the debris and fluid out & ease the irritation. The ears often become red & inflamed and normally develop an offensive odour. A yellowish moist discharge is often seen or indeed a dark brown crumbly discharge is evident (sometimes both!). Signs of infection by ear mites are generally a dark brown discharge which is crumbly like coffee grounds.

Causes

There may be several causes of ear infection, commonly ear mites or allergies are the cause or bacteria or yeast infection (Micro Organisms) is to blame. To bacteria, yeast & ear mites, the ear canal seems the ideal place to set up home. It's dark, warm, moist and often with a poor air flow, all ideal conditions! Typical yeast infection arise from Malassezia Pachydermatis.

Ear mites are small parasites which are a subspecies of the spider (they are very small and have 8 legs), commonly found mites in the ear canal of dogs are Otodectes cynotis. Despite the name 'ear' mite they can in fact live anywhere on the animal's body. Ear mites are very common, but still serious. Left untreated, they severely damage the ear canals & eardrum and can cause permanent hearing loss.

In cases of bacterial infection, the bacteria involved is usually Staphylococcus Intermedius, Proteus Mirabilis, and Pseudomonas Aeruginosa. The former usually clear up well with a course of antibiotics, however Pseudomonas bacteria infections are very resistant to antibiotics & often notoriously difficult to control.

Pseudomonas ear infections normally exude a fluidic discharge which is pus (yellow/green discharge), there is usually ulceration/inflammation of the ear canal and the discharge has a characteristic odour which smells very much like 'swamp/pond' water.

Ear infections can also be related to skin allergies, especially food hypersensitivity, it is important to address the allergy problem in addition to the infection so as to minimise recurring ear infections.

In the case of allergy induced ear infection, the allergen will cause the dog to scratch, the scratching then causes inflammation and heat and this provides an ideal breeding ground for the organisms that cause ear infections.

Dogs with Hypothyroidism (insufficient Thyroxine produced by the dog's thyroid gland) can suffer skin infections including chronic ear infections, symptoms of this condition include: dry hair coat, dry skin/dandruff, intolerance of cold weather, loss of hair, skin infections and regular unexplained ear infections.

If a dog has recurrent ear infections without an obvious cause it may be worth having a blood test done to determine the levels of circulating thyroid hormones (T4/T3). If hypothyroidism is diagnosed this can be treated inexpensively with replacement thyroxine tablets (Levothyroxine Sodium) and all symptoms associated with the condition should resolve. Treatment of hypothyroidism needs to be continued throughout the life of the dog.

Treatment

For ear mite infection the normal course of action is to use commercial ear preparations (drops) to kill the mites.  These are available from pet shops, however our preference would be to use a product purchased from the owners vet.  These products contain an insecticide, usually pyrethrin.

Many of the topical 'Spot On' flea/tick type preparations available from vets are also effective against ear mites, therefore a product such as "Advocate" may be beneficial (placed on the skin of the dog as recommended and NOT instilled into the ear!).

When treating a dog for ear mites, the lifecycle of the mite must be considered and treatment repeated as appropriate until all stages of the mites lifecycle have been covered. As previously mentioned, many ear mites live all over the body, including the feet and tail and therefore unless using a 'Spot-On' product, any topical drops should also be applied to the base of the tail & possibly between the toes (favourite hiding places!). Ear mites are also highly contagious (between cats & dogs) therefore ideally other pets in the household should receive treatment regardless of whether infestation is obvious.

For bacterial or yeast infections trim away excess hair from the opening to the ear canal (so fresh air can flow into the ear canal) and keep the ear canal clean. Gentle ear cleansers that remove the wax & alter the acid balance - pH level of the ear (depending on which type of bacteria is found on culture) should be used.

Topical (with or without steroids) and/or oral antibiotics should also be used as recommended by the owners vet. The choice of medication should be based on the culture results.

If yeast is the culprit, with or without bacterial infection, medication specifically targeted at treating yeast infections (coupled with antibacterial medication) should be used. It is thought that topical medication is more effective than systemic medication as the potency of systemic treatment is not fully utilized with ear infections therefore systemic treatment with antibiotics is an adjunct to topical treatment where the concentration of the dose is higher.

If the ear drum is intact i.e. not perforated, the ear canal can be periodically (prior to other treatment initially then every few days) flushed with a commercial flush (TrizULTRA - kills yeast & bacteria or TrizEDTA - kills bacteria) about 30 mins before any medications are instilled into the ear canal as this helps to remove debris/discharge to allow the medication to penetrate the skin without being diluted or being prevented from reaching the surface of the skin - if it sits on top of the discharge it is virtually useless!

If Pseudomonas is suspected Baytril or Marbocyl antibiotics often work, however some Pseudomonas infections are resistant in which case Antirobe may be tried.  Treatment for Pseudomonas needs to be lengthy.

Antirobe can only be safely used for a limited time but both Baytril or Marbocyl should probably be continued for a minimum of four weeks, preferably eight weeks as it is a tough bacteria to destroy.  Stopping antibiotic treatment too soon, even if the dog seems better i.e. symptoms have gone, leads to almost immediate reoccurrence and the likelihood of antibiotic resistance and further difficulties in treating the reoccurring infection.

The recommended dose of Baytril (to treat Pseudomonas) is a much higher dose than the standard dose based on 50 mg per 10kg of body weight (for Medium sized breeds). It is suggested that a dose of "150 mg per 10kg of body weight is the most appropriate dosing regime. The instillation of Baytril antibiotic drops is also beneficial in conjunction with oral Baytril treatment." - Vale Veterinary Referrals, Dursley, Gloucestershire.

Once medication is discontinued, flushing the ear with tromethamine (Tris)-ethylenediaminetetraacetic acid (EDTA) buffer solution a few times a week can help prevent relapse of Pseudomonas infections.

In severe ear infections, particularly with Pseudomonas, the use of none steroid anti-inflammatory medication to control pain is advisable.

Any ear infection that does not clear up easily with standard veterinary treatments should be further investigated by culture of the ears, this will pin point the causative agent and help an owner's vet work out the most appropriate medications.  The exception to this rule is when infection is caused by Pseudomonas.  Infection from this bacteria is normally obvious (see above) and a culture should automatically be performed (rather than trying basic medications first) as this organism needs treating quite aggressively from the outset with the 'right' antibiotic rather then broad-spectrum antibiotics commonly used as a first line of treatment.