Otitis Externa - Cat and Dog

Introduction

Otitis Externa is a disease caused by the non-burrowing mite Otodectes cynotis. It is the most common mite of cats and dogs worldwide and is also seen in foxes and ferrets. The mite feeds on surface tissue in the ear and debris. Pruritus is caused by irritation and the saliva of the mites, which is immunogenic. Secondary bacterial infection is common, resulting in purulent otitis externa which will require more treatment.

The classical presentation of Otodectes mite is otitis externa, which affects the external ear canal. In cats, another presentation can be seen, which is that of an ectopic infection where signs are seen on other body parts such as the tail. This is due to contact e.g. cats sleeping in a curled position would allow mites to infest that area.

Clinical Signs

Clinical signs include head shaking, scratching of the ear and even the development of an aural haematoma because of the two above signs. The animal may often resent this area being touched. A brown waxy exudate is produced and this later becomes crusty. If secondary bacterial infection has occurred then pus will also be seen in the ear canal.

Diagnosis

Clinical signs and history are indicative of the disease.

Visualisation of the mites via an auroscope will provide definitive diagnosis.

Treatment

Topical ear drops usually contain acaricide, fungicide, antibiotics and steroids. These should be dropped into the ear and the base of the ear then massaged to help the drops disperse. In cases of severe wax build up, ceruminolytics may be useful.

Selamectin as a spot on also acts to prevent Otodectes.

All in contact animals should be treated in the household as these may be asymptomatic carriers.

References

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science.
Bond, R. (2008) Dermatology Study Guide, Royal Veterinary College.
Foster, A, and Foll, C. (2003) BSAVA small animal dermatology (second edition), British Small Animal Veterinary Association
Fox, M and Jacobs, D. (2007) Parasitology Study Guide Part 1: Ectoparasites, Royal Veterinary College

Also see: Ear Mites in Ferrets