Case 12


Because Wyatt's pruritus did not resolve with resolution of the bacterial and yeast infections and a short course of prednisone to address allergic inflammation, it is now imperative to consider other pruritic flare factors such as occult sarcoptic mange and food allergy before changing Wyatt's therapy for atopic dermatitis.

Identifying the organism is the best way to diagnose sarcoptic mange. However, this can be difficult because only small numbers of mites may be present (the severe pruritus results from a common hypersensitivity to the mite), and skin scraping results are often negative. Thus, in cases in which you still suspect this infection and want to rule it out, using response to therapy as a diagnostic tool is recommended. (An indirect ELISA for the detection of IgG antibodies to Sarcoptes scabeii is available commercially in Europe, but this test is not currently offered in the United States.)


Match the parasiticide to its appropriate description.

A. Ivermectin

B. Selamectin

C. Spinosad



1. Topical insecticide with alpha2-adrenergic receptor agonist activity; not recommended for scabies treatment because of the possibility of mite resistance; toxic in cats

2. Can be used orally or by subcutaneous injection; enhances release of GABA, which blocks postsynaptic stimulation of the adjacent neuron in nematodes or muscle fiber in arthropods

3. Semi-synthetic avermectin applied topically every two weeks for three applications for treatment of sarcoptic mange1

4. Interferes with passage of chloride ions in GABA-regulated chloride channels, disrupting the insect's central nervous system activity

5.Causes hyperexcitation of the insect nervous system, leading to involuntary muscle contractions, prostration tremors, and, finally, paralysis and death

a) A-2, B-3, C-5, D-1, E-4

b) A-3, B-2, C-5, D-1, E-4

c) A-2, B-3, C-4, D-5, E-1

d) A-4, B-2, C-3, D-1, E-5

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