Small Mammals Q&A 05

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A mouse develops pruritus and hair loss over its dorsum. The skin appears reddened with multifocal crusts and patchy alopecia. Another mouse in the same cage is asymptomatic. There is also a 10-year-old Yorkshire terrier recently diagnosed with allergic dermatitis living in the same household.

Question	Answer		Article
What are the differential diagnoses for pruritus and alopecia in the mouse?	The causes of pruritus and alopecia in the mouse include ectoparasites, dermatophytosis, bacterial infections, barbering, pinworms and neoplasia. The more common ectoparasites include the parasitic mites Myobia musculi and Myocoptes musculinus. Less common species of mites include Radfordia affinis, Psorergates simplex, Otodectes bacoti, Sarcoptes scabiei, Notoedres muris and Trichoecius romboutsi. Other ectoparasites include fleas, primarily in households with dogs and cats. The louse, Polyplax serrata, is also considered. Dermatophytosis is an uncommon cause of pruritus in the mouse. Trichophyton mentagrophytes can be isolated from 60% of clinically normal pet shop mice. Bacterial dermatitis (i.e. Staphylococcus) is not typically pruritic but may cause skin crusting. Barbering, due to stress and overcrowding, causes alopecia but not pruritus. Pinworms cause a localized perianal pruritus. Neoplasia, such as epitheliotrophic lymphoma, occasionally causes alopecia and pruritus but generally is associated with scaly skin.		Link to Article
What diagnostic steps would you take to find the cause of the problem?	Perform skin scrapings, fungal cultures and skin biopsies to determine the cause.		Link to Article
What is the organism shown above and how would you treat it?	This Sarcoptes mite was found after a skin scraping. Two to three injections of ivermectin is usually sufficient to cause resolution of the signs. Insecticidal dips may be too toxic, even diluted, for mice. Use any insecticide product in mice with great caution.		Link to Article
What recommendations would you make regarding the other animals in the household?	Consider the other mouse an asymptomatic carrier and treat it with ivermectin. Since the dog may not be suffering from allergies but rather a mite infestation, it is important to examine all household pets and people for mites. The household environment should be thoroughly cleaned.		Link to Article