Scabies can take on many 'faces'

Canine scabies is often missed (reportedly 70 percent of the time) and should always be considered.

The signs of scabies can be subtle and include hock involvement.

Even though sarcoptic mange is a nonseasonal source of pruritus, in the Midwest this disease seems to surface most often in the summer and fall. Here are some tips for diagnosis and treatment.

Many faces

What is often misleading about scabies is the many "faces" with which it can present.

Classically the papular, crusty, ear edges, hocks, ventral abdomen, and/or elbows is the type of presentation we all wish to see. However, sometimes subtle clinical signs such as pruritus without lesions, weight loss, pruritus with peripheral lymphadenopathy, a patient with an "itchy" face often resulting in a corneal ulcer, or aural hematomas are clues to the diagnosis. When looking for crusty ear edges, beware of the owner who picks off the crusts during grooming as they will not be present.

Subtle signs of scabies include facial pruritus due to ear ridge involvement.

Without question the most difficult clinical presentation is the canine patient that is pruritic without lesions. Many differentials such as other ectoparasites, food allergy, Malassezia dermatitis, or atopy need to be considered. However if scabies is suspected, treatment should be undertaken before pursuing workups for allergy. Other clues to a possible diagnosis of scabies include exposure to other dogs either via kenneling or grooming, stray dogs roaming the neighborhood, exposure to a wolf, fox, or coyote (they carry canine scabies mites), an older dog that just started with pruritus, several dogs in the family that are pruritic, a new addition to the family that results in pruritus of the other pets, or a pruritic patient where immunosuppressive doses of steroid are needed to control the pruritus. We will occasionally see patients on chemotherapy protocols that contract scabies due to exposure to other pets with their immunocompromised status. One study indicated that hypothyroid patients may harbor large numbers of scabies mites, again possibly due to their reduced immune status.

A pruritic young Labrador Retriever with evidence of face rubbing and pedal pruritus. Differentials include atopy, food allergy, Malassezia dermatitis and scabies.

Challenging diagnosis

Not only can the clinical presentation of the patient with scabies be somewhat difficult, but the diagnosis can even be more of a challenge! To confirm the diagnosis, deep skin scrapings yielding blood need to be performed preferably on the ear edges, hocks, elbows or ventral abdomen, i.e. any of the papular, crusty areas. Confirmation of the mite, eggs, or fecal pellets observed under low power in oil is what we all wish to see. However, scabies can be present yet undetectable anywhere from 30-70 percent of the time. Other methods of diagnosis include fecal samples yielding mites or eggs, skin biopsies - somewhat suggestive of an ectoparasite hypersensitivity if the mite is not captured at the biopsy site, a positive ear edge/rear leg reflex (not specific and may be negative if there is no ear edge involvement), a serum ELISA test for scabies available in Europe, or positive reaction to house dust mite on skin testing (cross reactivity between mites). Aside from actually finding evidence of the mite on skin scrapings, perhaps the other most definitive method of diagnosis is response to therapy.

Whichever therapy is undertaken, it is important to remember to treat the environment where the scabies-affected patient or those exposed to that patient reside. The mite can live up to 21 days off the patient if temperature and humidity conditions are favorable. Treatment of the environment includes professional extermination or a house and carpet insecticide spray. Also consider treatment of other dogs exposed to the affected patient. Asymptomatic carriers may exist.

A Miniature Poodle never out of the house except for grooming has scabies affecting the ear ridge.

One report claimed the dog's pruritus did not subside until the household cat was treated. Reportedly the mite is transferable to other species including humans and can live on humans for up to six days. Since the mite prefers the canine species, pruritus in humans usually resolves once treatment for the dog is undertaken. Methods of treatment for canine patients include topicals such as amitraz dips every two weeks for a total of two dips, lime sulfur dips every five to seven days for at least one month, fipronil spray–l spritz/lb body weight every three weeks for two applications, or weekly Paramite dips for a total of four dips. Unfortunately topical therapies may result in treatment failures due to the application technique of the person applying the topical and the deep burrowing activity of the mite. Anecdotally, there have been reported pockets of Paramite "resistance" in some areas of the country. Again this may not be due to the actual "resistance" to the product but to other factors such as the dipping technique, re-exposure to the mite, or lack of treatment of the environment.

Hypothyroid patients may harbor large numbers of scabies mites due to their reduced immune status.

Systemic therapies for scabies include: Ivermectin 200ug/kg/week SQ or PO for three to six doses after testing negative for heartworm. It should not be used in herding breeds or mixes thereof. Ivermectin is not FDA approved for this use. Ivermectin should be used cautiously in elderly patients due to a possible increased incidence of neurological side effects such as ataxia. The subcutaneous method of administration may be irritating and result in abscesses (however the latter may be due to using contaminated solution from multiple use). Some report possible erratic absorption of ivermectin administered orally although that is my usual method of administration. Milbemycin, also not FDA approved for use for scabies, has been used at doses of l mg/kg every other day for 16 days or l mg/lb body weight once weekly for four weeks after first testing negative for heartworm. The advantage of milbemycin over ivermectin is that milbemycin appears to be safer to use in herding breeds. Revolution has been used once monthly for three doses or every 15 days for three doses as a treatment for scabies. Whichever of the above systemic treatments are used it is best to use one and not a combination. Since secondary bacterial infection is usually present due to the intense pruritus, antibiotics and antibacterial bathing will be helpful in controlling any pruritus associated with the pyoderma. Antipruritic doses of prednisone for a two- week period may be helpful while treating for eradication of the mite.

Scabies mites, eggs and fecal pellets as observed in oil, under low power.

Since part of the diagnostics for canine scabies is response to therapy, do not hesitate to treat for the mite should you suspect it and not find it. Often this is confusing when explained to the client. However most understand that the next step involves more expensive and time-consuming diagnostics that may not be needed should the patient respond to antimite therapy.

Suggested Reading

• C. Griffin, K. Kwochka, J. MacDonald, Current Veterinary Dermatology, Mosby, St. Louis, MO, 1993.

• D. Scott, W. Miller, C. Griffin, Muller & Kirk's Small Animal Dermatology, 6th Ed, Saunders, Philadelphia, PA, 2001.