Clinical Signs and Diagnosis

Most of the symptoms of lice infestation are secondary to skin irritation, including nonspecific pruritus, excoriations, an unkempt hair coat, seborrhea, and self-induced alopecia. In severe cases, anemia and weakness may occur, especially in young animals. In cats, a crusted papular dermatitis (miliary dermatitis) may develop. Pediculosis in both dogs and cats can be asymptomatic. The diagnosis is made by careful observation and visualization of adult lice on the skin or eggs (nits) attached to hair shafts. In some instances, taking an acetate tape impression of hair and debris may be necessary.

Treatment

Table 98-2 lists the various treatment options for pediculosis in dogs and cats. Pruritus may persist for 2 to 4 weeks after treatment. Environmental treatment usually is not required because lice do not survive off the host; however, thorough cleansing of bedding and grooming tools is recommended. Treatment of contact animals is recommended since some may be asymptomatic carriers. Lice are species specific and do not present a significant zoonotic risk to owners.

Clinical Signs and Diagnosis

Canine scabies is characterized by intense pruritus. It classically affects the pinnae, elbows, and hocks but also can affect sparsely haired areas of the body such as the ventral abdomen and limbs. Early erythematous papules progress rapidly to yellowish crusts, alopecia, excoriations, lichenification, hyperpigmentation, and seborrhea. Secondary bacterial pyoderma is common.

In some instances, dogs may have intense nonseasonal pruritus but minimal lesions (scabies incognito) at presentation. Minimally pruritic, crusted scabies (Norwegian scabies) caused by S. scabiei var. canis also has been reported in rare cases in immunosuppressed patients.

Demonstration of scabies mites on superficial skin scrapings is diagnostic of canine scabies. However, finding mites on scrapings often is difficult. Taking multiple wide, superficial scrapings from areas with crusting provides the best chance of observing adult mites, eggs, or feces. However, because adults may be present in very low numbers, negative findings on scrapings do not rule out this disease. The pinnal-pedal reflex (rubbing the convex portion of the pinna or ear margin against itself causes scratching with the back leg) may be present in more than 75% of dogs with scabies. An enzyme-linked immunosorbent assay for canine scabies antibodies has been evaluated and shown to have high sensitivity and specificity. Dogs with persistent intense pruritus should be considered for empirical treatment. In some studies, 30% of dogs with scabies have shown some response to corticosteroid treatment, so steroid responsiveness should not be considered to rule out scabies.

Treatment

In the author’s experience, systemic treatments are generally safe, highly effective, and easier for owners to administer than topical treatments. Only selamectin has a label claim for the treatment of sarcoptic mange in the dog. See Table 98-3 for treatment options for canine scabies.