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.