Problems in diagnosing scabies, a global disease in human and animal populations

Abstract

Scabies is a worldwide disease and a major public health problem in many developing countries, related primarily to poverty and overcrowding. In remote Aboriginal communities in northern Australia, prevalences of up to 50% among children have been described, despite the availability of effective chemotherapy. Sarcoptic mange is also an important veterinary disease engendering significant morbidity and mortality in wild, domestic, and farmed animals. Scabies is caused by the ectoparasitic mite Sarcoptes scabiei burrowing into the host epidermis. Clinical symptoms include intensely itchy lesions that often are a precursor to secondary bacterial pyoderma, septicemia, and, in humans, poststreptococcal glomerulonephritis. Although diagnosed scabies cases can be successfully treated, the rash of the primary infestation takes 4 to 6 weeks to develop, and thus, transmission to others often occurs prior to therapy. In humans, the symptoms of scabies infestations can mimic other dermatological skin diseases, and traditional tests to diagnose scabies are less than 50% accurate. To aid early identification of disease and thus treatment, a simple, cheap, sensitive, and specific test for routine diagnosis of active scabies is essential. Recent developments leading to the expression and purification of S. scabiei recombinant antigens have identified a number of molecules with diagnostic potential, and current studies include the investigation and assessment of the accuracy of these recombinant proteins in identifying antibodies in individuals with active scabies and in differentiating those with past exposure. Early identification of disease will enable selective treatment of those affected, reduce transmission and the requirement for mass treatment, limit the potential for escalating mite resistance, and provide another means of controlling scabies in populations in areas of endemicity.

FIG. 1.

Female scabies mite with egg, taken from skin scraping.

FIG. 2.

Scabies of the hand with secondary infection.

FIG. 3.

Crusted scabies of the feet.

FIG. 4.

Crusted scabies of the eyelid.

FIG. 5.

Crusted scabies in a patient with leprosy.

FIG. 6.

Crusted scabies with chronic secondary ulcers and depigmentation.

FIG. 7.

Crusts and alopecia in a dog with severe scabies.

FIG. 8.

Skin biopsy of crusted scabies showing mites in the epidermis with hyperkeratosis and inflammatory response.

FIG. 9.

Serial section of human scabies mite. Red shows binding of polyclonal S. scabiei anti-group 8 antibodies raised in rabbits to protein in vivo. (Courtesy of C. Willis, Queensland Institute of Medical Research, Brisbane, Queensland, Australia.)