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 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

Sarcoptes scabiei and scabies

The disease scabies, caused by the ectoparasitic mite, Sarcoptes scabiei, causes significant morbidity in humans and other mammals worldwide. However, there is limited data available regarding the molecular basis of host specificity and host-parasite interactions. Therefore, we sought to produce a draft genome for S. scabiei and use this to identify molecular markers that will be useful for phylogenetic population studies and to identify candidate protein-coding genes that are critical to the unique biology of the parasite. S. scabiei var. canis DNA was isolated from living mites and sequenced to ultra-deep coverage using paired-end technology. Sequence reads were assembled into gapped contigs using de Bruijn graph based algorithms. The assembled genome was examined for repetitive elements and gene annotation was performed using ab initio, and homology-based methods. The draft genome assembly was about 56.2 Mb and included a mitochondrial genome contig. The predicted proteome contained 10,644 proteins, ~67 % of which appear to have clear orthologs in other species. The genome also contained more than 140,000 simple sequence repeat loci that may be useful for population-level studies. The mitochondrial genome contained 13 protein coding loci and 20 transfer RNAs. Hundreds of candidate salivary gland protein genes were identified by comparing the scabies mite predicted proteome with sialoproteins and transcripts identified in ticks and other hematophagous arthropods. These include serpins, ferritins, reprolysins, apyrases and new members of the macrophage migration inhibitory factor (MIF) gene family. Numerous other genes coding for salivary proteins, metabolic enzymes, structural proteins, proteins that are potentially immune modulating, and vaccine candidates were identified. The genes encoding cysteine and serine protease paralogs as well as mu-type glutathione S-transferases are represented by gene clusters. S. scabiei possessed homologs for most of the 33 dust mite allergens. The draft genome is useful for advancing our understanding of the host-parasite interaction, the biology of the mite and its phylogenetic relationship to other Acari. The identification of antigen-producing genes, candidate immune modulating proteins and pathways, and genes responsible for acaricide resistance offers opportunities for developing new methods for diagnosing, treating and preventing this disease.

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Draft genome of the scabies mite

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.

S. Achar

Papers

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