IN ANIMALS continued
a
b
Adult Sarcoptes scabiei mite (a) and skin scraping showing mites and eggs (b)
• Clinical signs in dogs may be due to physical irritation caused by the presence of mites and/or hypersensitivity reactions to salivary antigens (type I, III and IV hypersensitivity reactions have been reported). 4 Type III hypersensitivity reactions may be associated with immune mediated glomerulonephritis. • Traumatic lesions due to self-mutilation can occur which vary in intensity from mild (uncommon) to severe. Secondary lesions including excoriations, erosions, crusts, lichenification and hyperpigmentation may follow the pruritus. Inappetence and weight loss can occur in severe and chronic infestations. Superficial secondary bacterial infections may develop, including pyoderma and Malassezia spp. dermatitis. 3,4 • Norwegian (or crusted) scabies, where large mite populations are present causing thick crusts on the face, lateral elbows
and other parts of the body, is a rare severe form of sarcoptic mange that can occur in animals with concurrent disease or immunosuppression. 4 DIAGNOSIS • Definitive diagnosis of canine sarcoptic mange is based on finding Sarcoptes mites in a skin scraping sample (sampling needs to be deep enough to examine the full thickness of the epidermis). A positive pinnal-pedal scratch reflex (rubbing of an ear margin triggers the ipsilateral hind leg to elicit a scratching reflex) is present in 75-90% of cases and is suggestive of sarcoptic mange in dogs with compatible clinical signs. 4,9 If no mites are visualised but lesions are strongly suggestive of sarcoptic mange, diagnosis can be based on a positive response to treatment with an effective acaricide. 3
TRANSMISSION
• Human infestation with Sarcoptes scabiei var. canis is via direct contact with infested animals or indirectly via contact with contaminated environments or fomites such as infested bedding. • Prolonged skin-to-skin contact between an infested animal and humans is a major source of transmission, with human lesions usually found in areas of direct contact. The transmission rate of Sarcoptes scabiei var. canis from dogs to humans is estimated at 10 to 50%. 10
IN HUMANS
PREVALENCE AND RISK FACTORS • Human scabies is mostly associated with the host adapted variety S. scabiei var. hominis; however, zoonotic disease caused by S. scabiei var. canis has been reported. A study in northern Australian communities where canine and human scabies are co-endemic demonstrated canine-derived
and human-derived S. scabiei populations are genetically distinct, however this finding has subsequently been questioned. 11,12 The role of dogs in the transmission of scabies in these communities remains unresolved. • Human scabies is more common in school-aged children, Indigenous communities and residential aged care facilities.
CONTENTS
77 Companion Animal Zoonoses Guidelines
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