THE MERCK VETERINARY MANUAL
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Mite Infestations

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Sarcoptes scabiei is a common mange mite in pigs and dogs, and Notoedres cati is common in cats throughout the world (also see Mange). In the USA, sarcoptic mange is rare in horses and sheep and is considered a reportable disease. Papular eruptions progress to scaling, crusting, and excoriations of the ear margins and other parts of the body. Pruritus is severe. Transmission is by direct contact with infected animals or contaminated fomites. Diagnosis is based on clinical signs, history, and discovery of mites from multiple skin scrapings. Negative scrapings do not exclude the diagnosis, however, because mites are often difficult to find. If the diagnosis is suspected, treatment should be instituted. Mites are much easier to find on skin scrapings of cats with notoedric acariasis. Treatment options include 2%–4% lime sulfur dips (safe in all species) every 5 days for 4–6 treatments, amitraz dips at a strength of 250 ppm (in dogs only) applied weekly for 4 to 6 treatments, and ivermectin at 200–300 mcg/kg, PO or SC, every 1–2 wk for 3–4 treatments. Treatment response is not consistent when using lime sulfur dips or amitraz in small animals; therefore, these topicals are not good options for a treatment trial (ie, mites are not found on skin scrapings). Oral milbemycin oxime has been reported to be safe and effective in the treatment of sarcoptic mange in dogs but is not FDA approved for this purpose. The recommended treatment protocol is 2 mg/kg once weekly for 4 to 6 treatments or twice weekly for 3 wk. Selamectin, also extra-label, has also shown efficacy; the recommended protocol is four applications at 2-wk intervals. Moreover, imidacloprid 10%/moxidectin 2.5% spot-on applied twice at a 30-day interval or every 3 wk for three treatments has been shown to be efficacious. There are also anecdotal reports of efficacy of these treatment modalities for treatment of notoedric mange in cats. Because mites can survive off the host for a variable amount of time, all bedding, brushes, tack, and fomites should be treated as well. All in-contact animals also should be treated because of the contagious nature of these acarioses.

Ivermectin is widely used to treat sarcoptic mange in dogs and has been used to treat notoedric mange in cats, but it is not approved by the FDA for these indications. Therefore, every caution should be taken, and clients specifically informed of inherent risks with this drug. Dog breeds susceptible to ivermectin toxicity include Collies, Shetland Sheepdogs, Australian Shepherds, English Shepherds, Longhaired Whippets, McNabs, Silken Windhounds, and Old English Sheepdogs. Before using ivermectin in any of these breeds, a genetic test for the mutation of the ABCB1 (formerly MDR1) gene, which encodes for the multidrug transporter P-glycoprotein, should be performed. (This test is available at the University of Washington.)

Nonburrowing psoroptic mites cause otitis externa in horses and goats. Animals may be asymptomatic or present with pruritus, head shaking, and a drooping ear. Crusted papules, alopecia, and/or scaling are typically present on the pinnae. Diagnosis is confirmed by finding the mites on skin scraping or in otic exudate, but mites may be difficult to find in the ear canal. Ivermectin at 200 mcg/kg, PO, every 2 wk for two treatments has been shown to be effective.

Last full review/revision October 2013 by Sheila M. F. Torres, DVM, MS, PhD, DACVD

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