Sarcoptic Mange

Sarcoptic mange is a cosmopolitan, transmissible, nonseasonal, highly pruritic, generalized dermatosis of dogs caused by Sarcoptes scabiei var cani. It is contagious among dogs and can cause transient lesions on humans because sarcoptic mange is a zoonosis.

The pinna is one of the favorite habitats of the mite. Early pinnal lesions are abun­dant, with yellowish crusts that adhere between hairs. The entire border of the pinna may be involved. Pruritus is usually intense and results in pinnal trauma, hair loss, excoriation, and erythema. Because the pathogenesis of scabies involves a hyper­sensitivity reaction, some dogs may experience only mild pruritus. An anergic form is described where affected animals are almost nonpruritic in spite of the presence of hundreds of mites.⁵ More commonly, clinical signs of scabies can be more subtle or have a different localization in dogs treated for fleas and ticks with drugs used against acarids (permethrin, other pyrethroids, fipronil, amitraz) that are not completely efficient due to their spectrum, the formulation used (spot-on, collars, shampoo), the amount used, or the frequency of application.

Differential diagnosis includes otodectic dermatitis, trombiculosis, pediculosis, cheyletiellosis, contact dermatitis, Malassezia dermatitis, and atopic dermatitis. Definitive diagnosis is based on finding Sarcoptes scabiei mites. Multiple skin scrap­ings are sometimes necessary and should involve at least both pinnae and both elbows. Pinnae should be sampled preferentially in areas where thin crusts are present. They feel like sand when the pinnal margins are palpated between the fingers. Nevertheless, mites can be difficult to find. If sarcoptic mange is suspected, a complete treatment should be instituted regardless of skin scraping results.

The pinnal-pedal reflex is often positive. When the pinnal margin is scratched with a fingernail, a reflexive rear leg scratch is initiated. Most pruritic conditions of the pinna and even pruritic otitis externa can also induce a positive response. False-negative reactions are also encountered.

Treatment for scabies should involve the whole body, even if lesions are localized. Systemic treatments (selamectin, ivermectin) are usually preferred because they are easy to use, have minimal side effects, and are environmentally safe. In case of treat­ment failure or for cost considerations, especially in kennels, acaricidal rinses are a good alternative (lime sulfur, amitraz, rotenone, phosmet). Hair clipping is mandatory if the hair coat is thick and/or long. Lime sulfur rinses can be used on young dogs.