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.

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

Scabies has been a scourge among human beings for thousands of years. Its worldwide occurrence with epidemics during war, famine, and overcrowding is responsible for an estimated 300 million people currently infested. Scabies refers to the various skin lesions produced by female mites, and their eggs and scybala that are deposited in the epidermis, leading to delayed-type hypersensitivity reaction. Recent immunological findings such as cross-reactivity with house dust mite allergens and an altered T-helper-1/T-helper-2 pattern contribute to a better understanding of the pathomechanism. Furthermore, progress in molecular biology and cloning of relevant antigens could enable the development of a diagnostic ELISA system and candidate vaccines in the near future. Typical and atypical clinical presentations with pruritus as a hallmark of scabies occur in young, pregnant, immunocompromised, and elderly patients and include bullous and crusted (Norwegian) manifestations as well as those masked by steroid use (scabies incognito). This article reviews scabies management strategies in developed countries and resource-poor communities as well as typical complications, including the emergence of resistance and drug-related adverse events. Other problems such as post-scabies eczema and reinfestation, and newer treatments such as ivermectin are also discussed.

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Scabies: a ubiquitous neglected skin disease

Scabies continues to be an important parasitic disease of humans, and other mammals. Suprisingly for a disease that has afflicted humans since antiquity, little is directly known about the basic biology of the parasite, the host-parasite interactions, the host immune response, and host susceptibility. Much more research in these areas is needed if we are to understand fully the occurrence, transmission, and epidemiology of both human and animal scabies.

Biology, Host Relations, and Epidemiology of Sarcoptes scabiei

The past several years have witnessed an upsurge of genomic data pertaining to the Mycobacterium avium complex (MAC). Despite clear advances, problems with the detection of MAC persist, spanning the tests that can be used, samples required for their validation, and the use of appropriate nomenclature. Additionally, the amount of genomic variability documented to date greatly outstrips the functional understanding of epidemiologically different subsets of the organism. In this review, we discuss how postgenomic insights into the MAC have helped to clarify the relationships between MAC organisms, highlighting the distinction between environmental and pathogenic subsets of M. avium. We discuss the availability of various genetic targets for accurate classification of organisms and how these results provide a framework for future studies of MAC variability. The results of postgenomic M. avium study provide optimism that a functional understanding of these organisms will soon emerge, with genomically defined subsets that are epidemiologically distinct and possess different survival mechanisms for their various niches. Although the status quo has largely been to study different M. avium subsets in isolation, it is expected that attention to the similarities and differences between M. avium organisms will provide greater insight into their fundamental differences, including their propensity to cause disease.

http://lib.ajaums.ac.ir/booklist/81827.pdf

Mycobacterium avium in the Postgenomic Era

The disease scabies is one of the earliest diseases of humans for which the cause was known. It is caused by the mite, Sarcoptes scabiei, that burrows in the epidermis of the skin of humans and many other mammals. This mite was previously known as Acarus scabiei DeGeer, 1778 before the genus Sarcoptes was established (Latreille 1802) and it became S. scabiei. Research during the last 40 years has tremendously increased insight into the mite’s biology, parasite-host interactions, and the mechanisms it uses to evade the host’s defenses. This review highlights some of the major advancements of our knowledge of the mite’s biology, genome, proteome, and immunomodulating abilities all of which provide a basis for control of the disease. Advances toward the development of a diagnostic blood test to detect a scabies infection and a vaccine to protect susceptible populations from becoming infected, or at least limiting the transmission of the disease, are also presented.

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A review of Sarcoptes scabiei: past, present and future.

Serum from seven patients with ordinary scabies and six with crusted scabies were screened by immunoblotting for IgE- and IgG-specific proteins in an extract of the mite, Sarcoptes scabiei variety canis. Sera from atopic individuals without sensitivity to house dust mites were used as controls. Serum from all of the patients with crusted scabies showed strong IgE binding to 11-21 and IgG binding to 1-7 scabies proteins. In contrast, three of the seven patients with ordinary scabies showed IgE binding to one to six scabies proteins, and their antibody binding was much weaker. Patients with crusted scabies had serum antibody that reacted with larger molecular weight proteins compared with patients with ordinary scabies. The results of this study indicate that patients with crusted scabies showed a pronounced IgE response to scabies mites, whereas patients with ordinary scabies did not.

Circulating IgE in patients with ordinary and crusted scabies

Adult female Sarcoptes scabiei var canis mites were applied to human skin for 96 hours in an experimental chamber Clinical lesions produced during this period were studied histologically, The organisms burrowed, defecated, and laid up to nine eggs that developed normally Two eggs hatched after removal from the host A life cycle was not completed during this short experiment, but these results suggest canine scabies are capable of such activities on human skin

Experimental canine scabies in humans

This study examines the energy relationship between the host and the ectoparasitic mite Sarcoptes scabiei var. canis. Parasitized rabbits during the first 14-wk, post-initial infestation gained weight at approximately the same rate, but they consumed more food and water than uninfested control rabbits. During weeks 17–42 after the initial infestation, infestation levels increased until 10–30% of the body area was heavily parasitized. During this time, infested rabbits steadily lost weight even though there was no marked difference in food consumption between infested and control rabbits. Oxygen consumption rates were 0.00206 and 0.00076 μl O2/h/mite for female and male mites, respectively, at 75% RH and 34°C. Based on these rates, mite density on the host, and the infested host body surface area, the energy demand by the mites on a heavily parasitized host was insignificant relative to the metabolic rate of the host. Parasite energy demand was not responsible for the weight loss or reduced weight gains exhibited by the parasitized hosts. All of the infested rabbits became free of mites within 2 wk after treatment with an acaricide and rapidly regained the lost weight.

Stephen A. Estes

Papers

Circulating IgE in patients with ordinary and crusted scabies

Experimental canine scabies in humans

Energetic relationships of Sarcoptes scabiei var. canis (Acari: Sarcoptidae) with the laboratory rabbit.