Ear Mites in Dogs and Cats

24 05 2011

Ear Mites in Dogs and Cats

Is your cat or dog constantly scratching at their ears or shaking their head?  Do the ears contain a dark brown to black crusty discharge that resembles “coffee grounds” but yet has a waxy consistency?   Does your pet have a hot spot below one of their ears?   Then your cat or dog could be suffering from an infection due to an infectious mite called Otodectes cynotis, more commonly referred to as ear mites.

O. cynotis is a large white mite, approximately 03 to 0.5 mm long that moves about freely on the surface of the skin in the ear canal.  This particular mite does not burrow in the various skin layers and instead feeds on sloughed surface skin cells, debris and available inflammatory exudates present on the surface of the ear canal and skin.  Although these mites prefer the ear canal environment, they can infest any part of the body.   These mites have been known to colonize the hair on the side of a pet’s face near the ear or may find themselves on the rump and tail area when the pet curls up to sleep.  The colonization of areas other than the ear canal is especially common when inflammation is so severe that the ear canal itself is not conducive to mite survival.

Ear Mites have eight legs.  Male mites have cup-shaped suckers and their legs extend in length beyond the outer margin of their body.  Female mites have only one pair of legs containing these cup-shaped suckers while the fourth pair of legs is rudimentary (smaller in size).  Ear mites can be easily seen on an otoscopic examination or on a smear of ear exudate viewed under a light microscope.

These mites are highly contagious to others through direct content with an infested cat or dog.  They are a potential zoonotic pathogen (capable of infecting people).

Ear mites are actually hardy and may survive off the host for at least 12 days.  The entire life cycle of the parasite takes place in the ear canal or on the hair coat of the infected individual.  The infection is also termed ear canker or otoacariasis.  The life span of an individual mite is 2 months.

Symptoms of an ear mite infection include: shaking of the head, itchiness (puritis), ear canal inflammation, and the presence of a dark, nearly black discharge within the ear canal.  A positive pinnal-pedal reflex (when you scratch the back of the ear the rear leg on that side of the body starts moving constantly in a scratching motion) may be seen in cats but not in dogs.  The intense puritis is often due to a hypersensitivity to various antigenic (protein) components in the mite’s saliva.  Ear mite antigens may cause cross-reactivity to house dust when allergy testing a dog for atopy (allergies) or asthma.  This cross-reactivity in turn may cause a pet to be incorrectly diagnosed as allergic to dust mites.

There is a variety of products available for the treatment of ear mites, from medications applied in the ears to those that are applied topically to the coat which kill or prevent other parasites in addition to ear mites such as fleas and ticks.  Over the counter products are available from Farnam, Happy Jack and Hartz Mountain.  Prescription products are available from Bayer, Pfizer, Novartis and Idexx Laboratories.  It is always advantageous to have the correct etiology for a particular ear infection before instigating treatment.  For conformation of an ear mite infection see your veterinarian before treatment for ear mites is begun or you may alternatively be treating a yeast infection incorrectly believing it to be an ear mite infestation.

An example of a topical prescription treatment is that of Acarexx® a 0.01% ivermectin otic (ear) suspension produced by Idexx Laboratories.  Acarexx® is approved for use in cats and kittens four weeks of age and older.  This product is very effective against adults but its efficacy against eggs and immature stages has not been proven.  Best results are obtained when the ears are thoroughly cleaned before applying.  In practice, I have seen the best results when the dose was repeated once at a three week interval.

Several products available as a heartworm and flea preventatives in cats that are also very effective in the control of ear mites.  Two such products are Advantage Multi® available from Bayer Animal Health and Revolution® marketed by Pfizer.  Each product is applied topically at the back of the head after parting the hair and applied directly to the skin.  The back of the head is the preferred site of application thereby preventing the cat from licking the medication off. Two to three applications may be necessary at a two week interval for complete resolution of the problem.

References:

Blagburn, Byron.  “Canine and Feline Otoacariasis – Ear Mites Revisited.”  Veterinary Forum.  April 2009.  Pp. 33-36.

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