Ear Mites
April, 2000
Ear mites are common parasites of domestic dogs and cats.
Unlike mange mites, they do not burrow into the skin, but live on
the surface. They prefer the ear canal, but can also be located
on the neck, rump and tail. Ear mite infestation leads to itchy
ears, so the outward signs we see include shaking the head and
scratching the ears.
The ear mite, Otodectes Cynotis, completes a life cycle in only
three weeks. The egg is laid with a cement that holds it in the
ear. After incubating for 4 days, it hatches to form a larva. The
larva feeds for 3 - 10 days before becoming a pre-adult and then
an adult. The adult mite feeds on debris and tissue fluid from
the outer layer of the skin. As the mites feed, the ear canal
becomes irritated and fills with wax, blood, and the mites waste
material. This discharge has been compared to coffee grounds in
appearance. Some cats have massive amounts of this discharge, but
minimal itchiness. Most dogs tend to have obvious itchiness at
the first sign of discharge. As previously mentioned these mites
can be found outside the ear canal, but they rarely cause
problems at these other locations unless a true allergy exists.
Ear mites are highly contagious and especially prevalent in the
young. They are spread by close contact and can live on many
species. They have even been known to cause a rare short-term
dermatitis in humans.
Treating the disease usually involoves applying medication
directly in the ear canal. Several miticidal agents are
available. Ear mites seem to be developing resistance to
pyrethrins, which is the most common pesticide found in
over-the-counter ear mite medications. The most effective ones
usually contain ingredients called ceruminolytic agents that help
breaking up and remove waxy debris. Most of these medications
should be applied for three weeks straight (1 life cycle) to
effectively eliminate all mites. One topical preparation
available from veterinarians, Tresaderm, also contains
thiobendazole. This ingredient also kills mite eggs, so the
course of treatment can be shortened to about 2 weeks and still
be effective. The familiar drug Ivermectin is also effective at
treating ear mites in dogs and cats when given subcutaneously or
orally. Most animals receive 2 doses, separated by 2 weeks. The
monthly spot-on, the most recently marketed kills a number of
both external and internal parasites, but would be a costly
treatment for ear mites alone.