Efficacy of selamectin administered topically in the treatment of feline otoacariosis.

The efficacy of a novel avermectin, selamectin (Stronghold, Pfizer), was evaluated against naturally acquired aural infestations of Otodectes cynotis. Selamectin was administered topically in a single spot to the skin of each animal's back at the base of the neck in front of the scapulae at a minimum dosage of 6mgkg(-1). Thirty cats of a cattery of 120 animals with an endemic infestation were treated on days 0 and 30. Including untreated control cats was therefore not possible because of animal welfare consideration. Clinical examination and visualization of mites by otoscopic examination of the external ear canal and microscopic examination of aural debris/exudate were performed twice weekly from days 0 to 30. On day 0 (and day 28 if the ears canals were erythematous), a swab was taken from each canal and sent to bacteriology and mycology units for detection and identification of bacteria (Staphylococcus mainly) and yeast (Malassezia pachydermatis only). Selamectin was safe, parasites were killed before day 3 and eliminated before day 17. Selamectin was 100% effective against natural aural infestations, even if erythema (26-33% of cats) and scratch reflex (23-40% of cats) persisted for 2 weeks after the cats tested negative for mites.