Always keep scabies in mind as a differential in your pruritic canine patient, and, remember, very few cases are typical.
Photo 1: Scabies eggs from a skin scraping in oil viewed under low power. (PHOTO COURTESY OF DR. ALICE JEROMIN)
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Canine scabies, or Sarcoptes scabiei var. canis is a transmissible infestation of the skin of dogs that is transferable to
other species. Scabies have a 17- to-21-day life cycle. The female mite excavates a burrow in the skin and lays her eggs behind
her (Photo 1).
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Photo 2: Canine scabies mite viewed under low power. (PHOTO COURTESY OF DR. ALICE JEROMIN)
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Mites prefer hairless skin. Canine scabies mites have a terminal anus vs. dorsal anus found in feline Notoedres cati (Photo
2). Preferred hosts include members of the canis species such as foxes, wolves, coyotes and dogs, but can cause disease in
other species such as cats and humans. Lesions on people consist of papules within 24 hours of exposure accompanied by pruritus.
Canine scabies mites on a person are difficult to isolate. Although they burrow, they will only remain on the unpreferred
host for a few hours to a few days. Pruritus can persist for several weeks following eradication of the mite.
Canine scabies have been found living on cats affected with mites. The off-host survival time is temperature and humidity
dependent. At room temperature, all mite stages can survive two to six days. Female mites at low temperature and high humidity
can survive off-host for four to 21 days. The incubation period is unknown but severe pruritus is evident at 21-30 days. Clinical signs and symptoms
Photo 3: Crusty ear edge of a Poodle with scabies mites. (PHOTO COURTESY OF DR. ALICE JEROMIN)
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Pruritus is usually nonresponsive to antipruritic or even immunosuppressive doses of steroids. If the dog is itchy despite
a high dose of steroids, be sure to consider scabies. Since the mite prefers nonhaired areas, affected areas include one or
more of the following: elbows, hocks, ventral abdomen and/or ear edges. Lesions range from none with just pruritus to crusting
(Photo 3) (be aware that owners sometimes "pick off" the crusts), excoriations, alopecia, lymphadenopathy, corneal ulceration
or aural hematomas.
Differential diagnoses
Differentials can include other ectoparasitic diseases such as Cheyletiella, atopy, Malassezia dermatitis, and food allergy.
Photo 4: Hypothyroid dog with scabies mites. (PHOTO COURTESY OF DR. ALICE JEROMIN)
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Suspect scabies if the dog has been exposed to other dogs via kennel or grooming; exposed to foxes, wolves, or coyotes; if
several dogs in the household are pruritic; if a new puppy comes into the household and pruritus starts; and in patients on
immunosuppressive doses of steroids for other internal medicine problems. Hypothyroid patients may have large numbers of mites
and not seem to be all that pruritic particularly if they are profoundly hypothyroid (Photo 4).
Diagnosis
Skin scrapings can yield mites, fecal pellets or eggs. (Keep in mind that scrapings may be negative up to 70 percent of the
time).
Other diagnostic techniques include:
» Skin biopsies (alluding to allergic dermatitis sometimes found with eosinophils)
» Positive ear-edge/rear-leg reflex (pinnal-pedal reflex) in atopic patients.
» Positive skin test reaction to house dust mites
» Serological test (available in Europe)
» A response to therapy ("Ivermectin response test")
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