In-depth Information for Sarcoptic Mange in Dogs
Sarcoptic mange is a contagious parasitic skin disease of dogs caused by Sarcoptes scabei. The mite is fairly host specific but can infest man and cause a transient pruritic papular eruption. In people lesions develop within 24 hours after exposure and spontaneously resolve in 12 to 14 days because the mite cannot reproduce on human skin.
The mite spends its entire life cycle on the host. The life cycle is complete in 17 to 21 days. Male mites live on the surface of the skin while females burrow into the superficial layers of the epidermis to lay eggs. Mites do not survive off the host longer than 48 hours in most conditions.
Incubation period for scabies varies from six to 30 days depending on previous exposure. If a dog has been exposed to the mite previously, clinical signs are more rapid and severe due to existent hypersensitivity.
Very few mites can cause severe clinical signs. This is most likely due to development of hypersensitivity from the host. Mite feces are the most likely source of antigenic stimulation.
Sarcoptic mange cannot be ruled out by the absence of clinical signs in other animals or people living in the same house. This is due to the limited number of parasites present in most affected animals.
Related Symptoms or Ailments The primary lesion is the pruritic erythematous papule, which is an itchy, red, raised skin bump. Later, these papules become associated with thick yellow-gray scale/crusts, especially on the ear. Sarcoptic mange has predilection for areas with sparse hair. Lesions are characteristically present at the edges of the pinnae, elbows, hocks and ventral chest and abdomen. It can become generalized. Secondary alopecia, skin thickening (lichenification) and hyperpigmentation can result from self-trauma. Excoriations are commonly seen. Erythema can become generalized.
Besides the classic presentation of scabies, there are two rarer syndromes: The first one is called “Scabies incognito” and is seen in well-groomed dogs. No skin lesions are seen in these dogs but intense pruritus is present. The second syndrome is called “Norwegian scabies” and is seen in young puppies, elderly patients or immunosuppressed dogs. In these cases pruritus is mild to non-existent but severe crusting and large numbers of mites are present. This presentation is probably caused by a lack of hypersensitivity reaction, which usually is the one that keeps the number of mites limited.
Diagnosis In-Depth of Canine Sarcoptic Mange
The diagnosis of sarcoptic mange is made on the basis of suggestive history, compatible clinical signs, microscopic examination of skin scrapings and response to therapy. Response to therapy sometimes is used as a diagnostic test because the sarcoptic mange mites can be very difficult to find on skin scrapings. Your veterinarian will probably recommend the following: Superficial skin scrapings. Most skin scrapings are positive for the sarcoptic mange mite in less than 50 percent of cases. Skin scrapings should be superficial and cover a broad expanse of skin. The best areas to scrape are the ear margins and elbows. Avoid areas of skin that the animal has mutilated. Areas with thick crusts are suitable areas. Fecal flotation. Mites may observed during microscopic examination of feces for parasites because the mites may be swallowed when the dog chews on its skin. Potassium hydroxide digestion of hair, crusts, and scales collected in large quantity. The material is digested in potassium hydroxide and centrifuged. This material is examined microscopically for mites and their eggs. Skin biopsy. Occasionally mites may be seen on microscopic examination of skin biopsy specimens, but this method is not a very sensitive. Papules are the best lesions to biopsy.
Treatment In-Depth of Sarcoptic Mange in Dogs
All extremely pruritic dogs with typical clinical symptoms should be treated. Dogs with non-seasonal pruritus that is poorly responsive to treatment with cortisone-like drugs (glucocorticoids) should be treated for sarcoptic mange to rule out this possibility.
All animals in the household should be treated. Various treatments may be used to eradicate sarcoptic mange mite infestation. They include: Lime sulfur (LymDip®) 2 to 4 percent: mix 4 to 6 ounces per gallon of water and apply once every 5 to 7 days for a total of 6 treatments. Lime sulfur is the treatment of choice for puppies less than 4 weeks old and animals that cannot be treated with ivermectin. Ivermectin should not be used in collies, shelties, Australian shepherds, or Old English sheepdogs due to the risk of serious and potentially life-threatening toxicity.
In dogs with long hair coats, the hair should be clipped to insure good contact of the product with the skin. Cleansing with a keratolytic (anti-dandruff) or antibacterial shampoo may advisable before using the lime sulfur dip. The dip should be applied thoroughly taking care not to miss any part of the body. Lime sulfur dip can dry the skin excessively and be irritating to some dogs. To decrease the drying effect of the dip, baby oil may be added to mixture.
Animals with white hair coats will turn yellow for a few days after treatment due to the presence of sulfur in the dip. The sulfur in the dip imparts a strong odor of “rotten eggs,” which may be very offensive. Lime sulfur also has an anti-pruritic effect, and temporary improvement even may be seen in dogs whose pruritus has a different cause. Ivermectin at a dosage of 300 micrograms/kg (0.3 mg/kg) given orally twice at 2-week intervals or given 4 times at weekly intervals can be used in some animals to treat sarcoptic mange. Treatment of sarcoptic mange with ivermectin represents an “off-label” use of the drug. Ivermectin should not be used in collies, shelties, Australian shepherds, Old English Sheep dogs. Ivermectin has been reported to cause life-threatening nervous system toxicity in these breeds.
In most dogs with sarcoptic mange, pruritus is reduced by at least 50 percent 7 to 10 days after the first treatment and pruritus gradually disappears within 4 weeks. Milbemycin (Interceptor®) at a dosage of 0.5 to 1 milligrams per pound of body weight once weekly for 4 weeks also is an effective treatment for sarcoptic mange. Milbemycin should be used with caution in ivermectin-sensitive breeds due to the potential of similar adverse effects. Amitraz (Mitaban®) also is an effective treatment for sarcoptic mange. It is not approved for this use however. To treat sarcoptic mange with amitraz, the drug is applied at the same concentration used for the treatment of demodectic mange (1 vial in 2 gallons of water) and administered as 3 to 4 dips given at 2 week intervals.
Amitraz should be used at 25 to 50 percent strength in toy breeds due to increased risk for toxicity in smaller breeds. Sedation is the most common adverse effect of amitraz. Amitraz should not be used in geriatric or sick animals and in those with diabetes mellitus because amitraz may cause a temporarily high blood sugar level. Selamectin (Revolution®) is an avermectin type drug that also can be used as treatment for sarcoptic mange. Selamectin is rapidly and completely absorbed through the skin and is safe for use in ivermectin-sensitive breeds. One treatment is sufficient to eradicate infestation. However, in severe cases a second application may be necessary. Bedding should be washed at high temperature or discarded. Vacuuming is recommended to eliminate possible reinfestation. Secondary bacterial skin infections are common and may require antibiotic therapy. Superficial bacterial infections often are treated for 4 weeks with antibiotics whereas deep infections may require treatment for 8 to 10 weeks.