Problems in Diagnosing Scabies, a Global Disease in Human and Animal Populations

Scabies is a common parasitic infection caused by the mite Sarcoptes scabiei. Infestations occur when the “itch” mite, S. scabiei, burrows into the skin and consumes host epidermis and sera. The predominant disease manifestations are mediated through inflammatory and allergy-like reactions to mite products, leading to intensely pruritic lesions. Scabies is a major global health problem in many indigenous and Third World communities. It causes outbreaks in nursing homes (99) and is recognized in those with human immunodeficiency virus and human T-cell leukemia virus type 1 infections (47, 48, 73, 97). Scabies is transmitted by skin-to-skin contact, as demonstrated in classical studies by Mellanby (79), who showed that direct person-to-person body contact was generally necessary for transmission of scabies. Thus, it is a disease of overcrowding and poverty rather than a reflection of poor hygiene (57). It has been estimated that 300 million people suffer from scabies infestation at any one time (102), although this number has been disputed (25). Scabies is an important disease of children, but it occurs in both sexes, at all ages, in all ethnic groups, and at all socioeconomic levels. Importantly, the associated mor bidity is frequently underestimated. In addition to the discomfort caused by the intensely pruritic lesions, infestations often become secondarily infected, especially with group A streptococci and Staphylococcus aureus. Epidemic acute poststreptococcal glomerulonephritis (APSGN) is often associated with endemic scabies in the affected community (29, 96). Despitethe availability of chemotherapy, repeated scabies infestations and the resultant recurrent pyoderma have now been identified as important cofactors in the extreme levels of renal and rheumatic heart disease observed in Aboriginal communities (30, 63, 112). Scabies is also a major problem among important livestock and companion animals, with, for example, approximately 25% of pigs in some areas of the United States experiencing scabietic mange, leading to major economic losses (22, 89). Moreover, many millions of wild animals worldwide suffer from sarcoptic mange. Even though this worldwide disease has been recognized throughout history, in the modern era there have been long interruptions and significant gaps in the research about scabies. Molecular studies of the parasite have been very limited, due to the generally low parasite burden and lack of an in vitro culture system. The first molecular studies of Sarcoptes scabiei var. hominis were enabled via the collection of large numbers of mites from the shed skin of crusted scabies patients in 1997 (107)