Mechanisms for a novel immune evasion strategy in the scabies mite sarcoptes scabiei: a multigene family of inactivated serine proteases

Evidence that Transcriptional Alterations in Sarcoptes scabiei Are under Tight Post-Transcriptional (microRNA) Control

Here, we explored transcriptomic differences among early egg (Ee), late egg (Le) and adult female (Af) stages of the scabies mite, Sarcoptes scabiei, using an integrative bioinformatic approach. We recorded a high, negative correlation between miRNAs and genes with decreased mRNA transcription between the developmental stages, indicating substantial post-transcriptional repression; we also showed a positive correlation between miRNAs and genes with increased mRNA transcription, suggesting indirect post-transcriptional regulation. The alterations in mRNA transcription between the egg and adult female stages of S. scabiei were inferred to be linked to metabolism (including carbohydrate and lipid degradation, amino acid and energy metabolism), environmental information processing (e.g., signal transduction and signalling molecules), genetic information processing (e.g., transcription and translation) and/or organismal systems. Taken together, these results provide insight into the transcription of this socioeconomically important parasitic mite, with a particular focus on the egg stage. This work encourages further, detailed laboratory studies of miRNA regulation across all developmental stages of S. scabiei and might assist in discovering new intervention targets in the egg stage of S. scabiei.

Comparative Genomics Reveals Insights into the Divergent Evolution of Astigmatic Mites and Household Pest Adaptations

Highly diversified astigmatic mites comprise many medically important human household pests such as house dust mites causing ∼1–2% of all allergic diseases globally; however, their evolutionary origin and diverse lifestyles including reversible parasitism have not been illustrated at the genomic level, which hampers allergy prevention and our exploration of these household pests. Using six high-quality assembled and annotated genomes, this study not only refuted the monophyly of mites and ticks, but also thoroughly explored the divergence of Acariformes and the diversification of astigmatic mites. In monophyletic Acariformes, Prostigmata known as notorious plant pests first evolved, and then rapidly evolving Astigmata diverged from soil oribatid mites. Within astigmatic mites, a wide range of gene families rapidly expanded via tandem gene duplications, including ionotropic glutamate receptors, triacylglycerol lipases, serine proteases and UDP glucuronosyltransferases. Gene diversification after tandem duplications provides many genetic resources for adaptation to sensing environmental signals, digestion, and detoxification in rapidly changing household environments. Many gene decay events only occurred in the skin-burrowing parasitic mite Sarcoptes scabiei. Throughout the evolution of Acariformes, massive horizontal gene transfer events occurred in gene families such as UDP glucuronosyltransferases and several important fungal cell wall lytic enzymes, which enable detoxification and digestive functions and provide perfect drug targets for pest control. This comparative study sheds light on the divergent evolution and quick adaptation to human household environments of astigmatic mites and provides insights into the genetic adaptations and even control of human household pests.

Serine pseudoproteases in physiology and disease

Serine proteases (SPs) constitute a very important family of enzymes, both physiologically and pathologically. The effects produced by these proteins have been explained by their proteolytic activity. However, the discovery of pharmacologically active SP molecules that show no enzymatic activity, as the so-called pseudo SPs or SP homologs (SPHs), has exposed a profoundly neglected possibility of nonenzymatic functions of these SP molecules. In this review, the most thoroughly described SPHs are presented. The main physiological domains in which SPHs operate appear to be in reproduction, embryonic development, immune response, host defense, and hemostasis. Hitherto unexplained actions of SPs should therefore be considered also as the result of the ligand-like attributes of SPs. The gain of a novel function by an SPH is a consequence of specific amino acid replacements that have resulted in a novel interaction interface or a 'catalytic trap'. Unraveling the SP/SPH interactome will provide a description of previously unknown physiological functions of SPs/SPHs, aiding the creation of innovative medical approaches.

Scabies itch: an update on neuroimmune interactions and novel targets

Frequently described as 'the worst itch' one can ever experience scabies itch is the hallmark of Sarcoptes scabiei mite infestation. Notably, the itchiness often persists for weeks despite scabicides therapy. The mechanism of scabies itch is not yet fully understood, and effective treatment modalities are still missing which can severely affect the quality of life. The aim of this review is to provide an overview of the scope of itch in scabies and highlight candidate mechanisms underlying this itch. We herein discuss scabies itch, with a focus on the nature, candidate underlying mechanisms and treatment options. We also synthesize this information with current understanding of the mechanisms contributing to non-histaminergic itch in other conditions. Itch is a major problem in scabies and can lead to grave consequences. We provide the latest insights on host-mite interaction, secondary microbial infection and neural sensitization with special emphasis on keratinocytes and mast cells to better understand the mechanism of itch in scabies. Also, the most relevant current modalities remaining under investigation that possess promising perspectives for scabies itch (i.e. protease-activated receptor-2 (PAR-2) inhibitor, Mas-related G protein-coupled receptor X2 (MRGPRX2) antagonist) are discussed. Greater understanding of these diverse mechanisms may provide a rational basis for the development of improved and targeted approaches to control itch in individuals with scabies.

A unique group of scabies mite pseudoproteases promotes cutaneous blood coagulation and delays plasmin-induced fibrinolysis

BACKGROUND

Scabies, a highly contagious skin disease affecting more than 200 million people worldwide at any time, is caused by the parasitic mite Sarcoptes scabiei. In the absence of molecular markers, diagnosis requires experience making surveillance and control challenging. Superficial microthrombi in the absence of vasculitis in scabies-affected skin are a recognised, yet unexplained histopathological differential of scabies infection. This study demonstrates that a family of Scabies Mite Inactivated Cysteine Protease Paralogues (SMIPP-Cs) excreted by the mites plays a role in formation of scabies-induced superficial microthrombi.

METHODOLOGY/PRINCIPAL FINDINGS

A series of in vitro and ex vivo experiments involving two representative recombinant SMIPP-Cs was carried out. In the presence of SMIPP-Cs, the thrombin clotting time (TCT), fibrin formation and plasmin induced fibrinolysis were monitored in vitro. The ultrastructure of the SMIPP-C-modulated fibrin was analysed by Scanning Electron Microscopy (SEM). Immuno-histological analyses were performed ex vivo, to localise the SMIPP-C proteins within scabies infected skin biopsies. SMIPP-Cs displayed pro-coagulant properties. They bound calcium ions, reduced the thrombin clotting time, enhanced the fibrin formation rate and delayed plasmin-induced fibrinolysis. The SMIPP-Cs associated with fibrin clots during fibrinogen polymerisation and did not bind to preformed fibrin. Scanning electron microscopy revealed that the fibrin clots formed in the presence of SMIPP-Cs were aberrant and denser than normal fibrin clots. SMIPP-Cs were detected in microthrombi which are commonly seen in scabietic skin.

CONCLUSIONS/SIGNIFICANCE

The SMIPP-Cs are the first scabies mite proteins found in sub-epidermal skin layers and their pro-coagulant properties promote superficial microthrombi formation in scabetic skin. Further research is needed to evaluate their potential as diagnostic or therapeutic target.

Molecular drug targets for scabies: a medicinal chemistry perspective

Sarcoptes scabiei is a causative organism for scabies that affects an estimated global population of 300 million and remains a disease of significant concern. Recently, a number of potential drug targets were identified for scabies, including hydrolytic enzymes, inactivated paralogues of hydrolytic enzymes, inhibitors of host proteolytic enzymes and other proteins of interest. These discoveries remain confined to academic laboratories and institutions, failing to attract interest from researchers in commercial drug development. Here, we summarize the latest developments in the scabies mite biology and the drug targets that were subsequently identified, and we propose several peptide and nonpeptide ligands targeting the hot spots for protein-protein interactions. We also identify gaps in the development of ligands as inhibitors or modulators of these macromolecules.

Inactivated tetanus as an immunological smokescreen: A major step towards harnessing tetanus-based therapeutics

BACKGROUND AND PURPOSE

Tetanus neurotoxin has many potential therapeutic applications, due to its ability to increase localised muscle tone when injected directly into a muscle. It is a closely related molecule to botulinum neurotoxin (most commonly known as Botox), which has been widely used to release muscle tension for therapeutic and cosmetic applications. However, tetanus toxin has been relegated to the "maybe pile" for protein therapeutics - as most of the population is vaccinated, leading to highly effective antibody-mediated protection against the toxin. The potential for tetanus-based therapeutics remains substantial if the problem of pre-existing immunity can be resolved.

EXPERIMENTAL APPROACH

A well-established murine model of localised muscular contraction was utilised. We administered functional tetanus toxin combined with an immunogenic, but functionally inactive, decoy molecule.

KEY RESULTS

Incorporation of the decoy molecule greatly reduces the dose of active toxin required to induce a localised increase in muscle tone in mice vaccinated with the human toxoid vaccine.

CONCLUSION AND IMPLICATIONS

Our results clearly demonstrate that the barriers to developing a tetanus toxin therapeutic are not insurmountable and the technology presented here is the first major step towards realising the therapeutic potential of this powerful neurotoxin. Opening the therapeutic potential of tetanus toxin will have huge implications for the wide range of diseases caused by low-tone muscle.

Harnessing helminth-driven immunoregulation in the search for novel therapeutic modalities

Parasitic helminths have coevolved with humans over millennia, intricately refining and developing an array of mechanisms to suppress or skew the host’s immune system, thereby promoting their long-term survival. Some helminths, such as hookworms, cause little to no overt pathology when present in modest numbers and may even confer benefits to their human host. To exploit this evolutionary phenomenon, clinical trials of human helminth infection have been established and assessed for safety and efficacy for a range of immune dysfunction diseases and have yielded mixed outcomes. Studies of live helminth therapy in mice and larger animals have convincingly shown that helminths and their excretory/secretory products possess anti-inflammatory drug-like properties and represent an untapped pharmacopeia. These anti-inflammatory moieties include extracellular vesicles, proteins, glycans, post-translational modifications, and various metabolites. Although the concept of helminth-inspired therapies holds promise, it also presents a challenge to the drug development community, which is generally unfamiliar with foreign biologics that do not behave like antibodies. Identification and characterization of helminth molecules and vesicles and the molecular pathways they target in the host present a unique opportunity to develop tailored drugs inspired by nature that are efficacious, safe, and have minimal immunogenicity. Even so, much work remains to mine and assess this out-of-the-box therapeutic modality. Industry-based organizations need to consider long-haul investments aimed at unraveling and exploiting unique and differentiated mechanisms of action as opposed to toe-dipping entries with an eye on rapid and profitable turnarounds.

Isoforms of Cathepsin B1 in Neurotropic Schistosomula of Trichobilharzia regenti Differ in Substrate Preferences and a Highly Expressed Catalytically Inactive Paralog Binds Cystatin

Schistosomula (the post-infective stages) of the neurotropic schistosome Trichobilharzia regenti possess multiple isoforms of cathepsin B1 peptidase (TrCB1.1-TrCB1.6) with involvement in nutrient digestion. The comparison of substrate preferences of TrCB1.1 and TrCB1.4 showed that TrCB1.4 had a very narrow substrate specificity and after processing it was less effective toward protein substrates when compared to TrCB1.1. Self-processing of both isoforms could be facilitated by sulfated polysaccharides due to a specific binding motif in the pro-sequence. Trans-activation by heterologous enzymes was also successfully employed. Expression profiling revealed a high level of transcription of genes encoding the enzymatically inactive paralogs TrCB1.5 and TrCB1.6. The transcription level of TrCB1.6 was comparable with that of TrCB1.1 and TrCB1.2, the most abundant active isoforms. Recombinant TrCB1.6wt, a wild type paralog with a Cys29-to-Gly substitution in the active site that renders the enzyme inactive, was processed by the active TrCB1 forms and by an asparaginyl endopeptidase. Although TrCB1.6wt lacked hydrolytic activity, endopeptidase, but not dipeptidase, activity could be restored by mutating Gly29 to Cys29. The lack of exopeptidase activity may be due to other mutations, such as His110-to-Asn in the occluding loop and Asp224-to-Gly in the main body of the mature TrCB1.6, which do not occur in the active isoforms TrCB1.1 and TrCB1.4 with exopeptidase activity. The catalytically active enzymes and the inactive TrCB1.6 paralog formed complexes with chicken cystatin, thus supporting experimentally the hypothesis that inactive paralogs could potentially regulate the activity of the active forms or protect them from being inhibited by host inhibitors. The effect on cell viability and nitric oxide production by selected immune cells observed for TrCB1.1 was not confirmed for TrCB1.6. We show here that the active isoforms of TrCB1 have different affinities for peptide substrates thereby facilitating diversity in protein-derived nutrition for the parasite. The inactive paralogs are unexpectedly highly expressed and one of them retains the ability to bind cystatins, likely due to specific mutations in the occluding loop and the enzyme body. This suggests a role in sequestration of inhibitors and protection of active cysteine peptidases.

Phylogenetic Distribution and Diversity of Bacterial Pseudo-Orthocaspases Underline Their Putative Role in Photosynthesis

Orthocaspases are prokaryotic caspase homologs - proteases, which cleave their substrates after positively charged residues using a conserved histidine - cysteine (HC) dyad situated in a catalytic p20 domain. However, in orthocaspases pseudo-variants have been identified, which instead of the catalytic HC residues contain tyrosine and serine, respectively. The presence and distribution of these presumably proteolytically inactive p20-containing enzymes has until now escaped attention. We have performed a detailed analysis of orthocaspases in all available prokaryotic genomes, focusing on pseudo-orthocaspases. Surprisingly we identified type I metacaspase homologs in filamentous cyanobacteria. While genes encoding pseudo-orthocaspases seem to be absent in Archaea, our results show conservation of these genes in organisms performing either anoxygenic photosynthesis (orders Rhizobiales, Rhodobacterales, and Rhodospirillales in Alphaproteobacteria) or oxygenic photosynthesis (all sequenced cyanobacteria, except Gloeobacter, Prochlorococcus, and Cyanobium). Contrary to earlier reports, we were able to detect pseudo-orthocaspases in all sequenced strains of the unicellular cyanobacteria Synechococcus and Synechocystis. In silico comparisons of the primary as well as tertiary structures of pseudo-p20 domains with their presumably proteolytically active homologs suggest that differences in their amino acid sequences have no influence on the overall structures. Mutations therefore affect most likely only the proteolytic activity. Our data provide an insight into diversification of pseudo-orthocaspases in Prokaryotes, their taxa-specific distribution, and allow suggestions on their taxa-specific function.

Tackling scabies: novel agents for a neglected disease

The scabies mite, Sarcoptes scabiei var hominis, is an obligate ectoparasite of humans. It has been a source of distress for humanity since antiquity. The troublesome mite is emerging triumphant over current acaricidal agents with reports of emerging resistance and treatment failures. Scabies in endemic areas and crusted scabies offer additional management challenges. Exploration of indigenous plants and better understanding of mite biology and pathogenesis provide opportunities for the development of novel agents for this common pest. We review the recent diverse approaches to scabies, including the use of novel plant products with a better safety profile, translating the use of moxidectin from veterinary practice to human scabies, vaccination, immunotherapy, and development of drugs that directly target mite molecules.

Phylogenetic relationships, stage-specific expression and localisation of a unique family of inactive cysteine proteases in Sarcoptes scabiei

Background

Scabies is worldwide one of the most common, yet neglected, parasitic skin infections, affecting a wide range of mammals including humans. Limited treatment options and evidence of emerging mite resistance against the currently used drugs drive our research to explore new therapeutic candidates. Previously, we discovered a multicopy family of genes encoding cysteine proteases with their catalytic sites inactivated by mutation (SMIPP-Cs). This protein family is unique in parasitic scabies mites and is absent in related non-burrowing mites. We postulated that the SMIPP-Cs have evolved as an adaptation to the parasitic lifestyle of the scabies mite. To formulate testable hypotheses for their functions and to propose possible strategies for translational research we investigated whether the SMIPP-Cs are common to all scabies mite varieties and where within the mite body as well as when throughout the parasitic life-cycle they are expressed.

Results

SMIPP-C sequences from human, pig and dog mites were analysed bioinformatically and the phylogenetic relationships between the SMIPP-C multi-copy gene families of human, pig and dog mites were established. Results suggest that amplification of the SMIPP-C genes occurred in a common ancestor and individual genes evolved independently in the different mite varieties. Recombinant human mite SMIPP-C proteins were produced and used for murine polyclonal antibody production. Immunohistology on skin sections from human patients localised the SMIPP-Cs in the mite gut and in mite faeces within in the epidermal skin burrows. SMIPP-C transcription into mRNA in different life stages was assessed in human and pig mites by reverse transcription followed by droplet digital PCR (ddPCR). High transcription levels of SMIPP-C genes were detected in the adult female life stage in comparison to all other life stages.

Conclusions

The fact that the SMIPP-Cs are unique to three Sarcoptes varieties, present in all burrowing life stages and highly expressed in the digestive system of the infective adult female life stage may highlight an essential role in parasitism. As they are excreted from the gut in scybala they presumably are able to interact or interfere with host proteins present in the epidermis.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2862-0) contains supplementary material, which is available to authorized users.

Sarcoptic mange in wombats-A review and future research directions

Sarcoptic mange is caused by the mite Sarcoptes scabiei and has recently been recognized as an emerging infectious disease of wildlife worldwide. The mite is one of the main causes of population decline in southern hairy-nosed (Lasiorhinus latifrons) and bare-nosed wombats (Vombatus ursinus). This review focuses on Sarcoptes scabiei infestations in wombats and provides insights into why the disease may be so prevalent in wombats. Current treatment practices and trials conducted in the field to reduce the incidence of sarcoptic mange in wombats are described and critically reviewed. Current and potential future avenues of research are discussed.

Identification of a novel PYP-1 gene in Sarcoptes scabiei and its potential as a serodiagnostic candidate by indirect-ELISA

Scabies is a parasitic disease caused by the ectoparasite Sarcoptes scabiei, affecting different mammalian species, including rabbits, worldwide. In the present study, we cloned and expressed a novel inorganic pyrophosphatase, Ssc-PYP-1, from S. scabiei var. cuniculi. Immunofluorescence staining showed that native Ssc-PYP-1 was localized in the tegument around the mouthparts and the entire legs, as well as in the cuticle of the mites. Interestingly, obvious staining was also observed on the fecal pellets of mites and in the integument of the mites. Based on its good immunoreactivity, an indirect enzyme-linked immunosorbent assay (ELISA) using recombinant Ssc-PYP-1 (rSsc-PYP-1) as the capture antigen was developed to diagnose sarcoptic mange in naturally infected rabbits; the assay had a sensitivity of 92·0% and specificity of 93·6%. Finally, using the rSsc-PYP-1-ELISA, the Ssc-PYP-1 antibody from 10 experimentally infected rabbits could be detected from 1 week post-infection. This is the first report of S. scabiei inorganic pyrophosphatase and the protein could serve as a potential serodiagnostic candidate for sarcoptic mange in rabbits.

Characterization of Sarcoptes scabiei Tropomyosin and Paramyosin: Immunoreactive Allergens in Scabies

Scabies is a human skin disease due to the burrowing ectoparasite Sarcoptes scabiei var. hominis resulting in intense itching and inflammation and manifesting as a skin allergy. Because of insufficient mite material and lack of in vitro propagation system for antigen preparation, scabies is a challenging disease to develop serological diagnostics. For allergen characterization, full-length S. scabiei tropomyosin (Sar s 10) was cloned, expressed in pET-15b, and assessed for reactivity with IgE antibodies from human sera. IgE binding was observed to Sar s 10 with sera collected from subjects with ordinary scabies, house dust mite (HDM)-positive and naive subjects and a diagnostic sensitivity of < 30% was observed. S. scabiei paramyosin (Sar s 11) was cloned, and expressed in pET-28a in three overlapping fragments designated Sspara1, Sspara2, and Sspara3. IgE and IgG binding was observed to Sspara2 and Sspara3 antigens with sera collected from ordinary scabies, and HDM-positive subjects, but no binding was observed with sera collected from naive subjects. Sspara2 displayed excellent diagnostic potential with 98% sensitivity and 90% specificity observed for IgE binding and 70% sensitivity for IgG. In contrast, the diagnostic sensitivity of Sspara3 was 84% for IgE binding and 40% for IgG binding. In combination, Sspara2 and Sspara3 provided an IgE sensitivity of 94%. This study shows that IgE binding to Sspara2 and Sspara3 is a highly sensitive method for diagnosis of scabies infestation in clinical practice. The developed enzyme-linked immunosorbent assay helps direct future development of a specific diagnostic tool for scabies.

Expression and characterisation of a Sarcoptes scabiei protein tyrosine kinase as a potential antigen for scabies diagnosis

Scabies is a disease that harms humans and other animals that is caused by the itch mite Sarcoptes scabiei burrowing into the stratum corneum of the skin. In the early stages of scabies, symptoms are often subclinical and there are no effective diagnostic methods. Herein, we cloned, expressed and characterised an S. scabiei protein tyrosine kinase (SsPTK) and evaluated its diagnostic value as a recombinant antigen in rabbit during the early stages of Sarcoptes infestation. The SsPTK protein is ~30 kDa, lacks a signal peptide, and shares high homology with a PTK from the rabbit ear mite Psoroptes ovis cuniculi. The protein was widely distributed at the front end of mites, particularly in the chewing mouthparts and legs. Indirect ELISA using recombinant SsPTK showed good diagnostic value, with 95.2% (40/42) sensitivity and 94.1% (48/51) specificity for detecting anti-PTK antibody in serum samples from naturally-infested rabbits. More importantly, PTK ELISA could diagnose infection in the early stages (infestation for 1 week) with an accuracy of 100% (24/24). SsPTK therefore shows potential as a sensitive antigen for the early diagnosis of parasitic mite infestation.

Allergen homologs in the Euroglyphus maynei draft genome

Euroglyphus maynei is a house dust mite commonly found in homes worldwide and is the source of allergens that sensitize and induce allergic reactions in humans. It is the source of species-specific allergens as well as allergens that are cross-reactive with the allergens from house dust mites Dermatophagoides farinae and D. pteronyssinus, and the ectoparasitic scabies mite Sarcoptes scabiei. The genomics, proteomics and molecular biology of E. maynei and its allergens have not been as extensively investigated as those of D. farinae, D. pteronyssinus, and S. scabiei where natural and recombinant allergens from these species have been characterized. Until now, little was known about the genome of E. maynei and it allergens but this information will be important for producing recombinant allergens for diagnostic and therapeutic purposes and for understanding the allergic response mechanism by immune effector cells that mediate the allergic reaction. We sequenced and assembled the 59 Mb E. maynei genome to aid the identification of homologs for known allergenic proteins. The predicted proteome shared orthologs with D. farinae and S. scabiei, and included proteins with homology to more than 30 different groups of allergens. However, the majority of allergen candidates could not be assigned as clear orthologs to known mite allergens. The genomic sequence data, predicted proteome, and allergen homologs identified from E. maynei provide insight into the relationships among astigmatid mites and their allergens, which should allow for the development of improved diagnostics and immunotherapy.

A review of Sarcoptes scabiei: past, present and future

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.

Gene silencing by RNA interference in Sarcoptes scabiei: a molecular tool to identify novel therapeutic targets

BACKGROUND

Scabies is one of the most common and widespread parasitic skin infections globally, affecting a large range of mammals including humans, yet the molecular biology of Sarcoptes scabiei is astonishingly understudied. Research has been hampered primarily due to the difficulty of sampling or culturing these obligatory parasitic mites. A further and major impediment to identify and functionally analyse potential therapeutic targets from the recently emerging molecular databases is the lack of appropriate molecular tools.

METHODS

We performed standard BLAST based searches of the existing S. scabiei genome databases using sequences of genes described to be involved in RNA interference in Drosophila and the mite model organism Tetranychus urticae. Experimenting with the S. scabiei mu-class glutathione S-transferase (SsGST-mu1) as a candidate gene we explored the feasibility of gene knockdown in S. scabiei by double-stranded RNA-interference (dsRNAi).

RESULTS

We provide here an analysis of the existing S. scabiei draft genomes, confirming the presence of a double stranded RNA (dsRNA) - mediated silencing machinery. We report for the first time experimental gene silencing by RNA interference (RNAi) in S. scabiei. Non-invasive immersion of S. scabiei in dsRNA encoding an S. scabiei glutathione S-transferase mu-class 1 enzyme (SsGST-mu1) resulted in a 35% reduction in the transcription of the target gene compared to controls.

CONCLUSIONS

A series of experiments identified the optimal conditions allowing systemic experimental RNAi without detrimental side effects on mite viability. This technique can now be used to address the key questions on the fundamental aspects of mite biology and pathogenesis, and to assess the potential therapeutic benefits of silencing S. scabiei target genes.

Treatment and control of Trixacarus caviae infestation in a conventional guinea pig (Cavia porcellus) breeding colony

A case of sarcoptic mange caused by Trixacarus caviae in a conventional guinea pig breeding colony is reported. The infestation was reported in a large colony of guinea pigs during the month of July, 2013 affecting 30 breeder guinea pigs. Severely infested animals were treated individually with subcutaneous injection of ivermectin 1 % w/v (Neomec^®) at the rate of 400 µg/kg body weight 10 days apart. Three doses of ivermectin were sufficient to eliminate the parasite which tested negative after 30 days of the first treatment. The entire colony was given preventive dose of ivermectin spray (2 mg/ml solution) following the same schedule. Strict hygienic measures were followed. New hair growth in the severely affected animals was evidenced on 30th day of treatment.

Identification of the Mamestra configurata (Lepidoptera: Noctuidae) peritrophic matrix proteins and enzymes involved in peritrophic matrix chitin metabolism

The peritrophic matrix (PM) is essential for insect digestive system physiology as it protects the midgut epithelium from damage by food particles, pathogens, and toxins. The PM is also an attractive target for development of new pest control strategies due to its per os accessibility. To understand how the PM performs these functions, the molecular architecture of the PM was examined using genomic and proteomic approaches in Mamestra configurata (Lepidoptera: Noctuidae), a major pest of cruciferous oilseed crops in North America. Liquid chromatography-tandem mass spectrometry analyses of the PM identified 82 proteins classified as: (i) peritrophins, including a new class with a CBDIII domain; (ii) enzymes involved in chitin modification (chitin deacetylases), digestion (serine proteases, aminopeptidases, carboxypeptidases, lipases and α-amylase) or other reactions (β-1,3-glucanase, alkaline phosphatase, dsRNase, astacin, pantetheinase); (iii) a heterogenous group consisting of polycalin, REPATs, serpin, C-Type lectin and Lsti99/Lsti201 and 3 novel proteins without known orthologs. The genes encoding PM proteins were expressed predominantly in the midgut. cDNAs encoding chitin synthase-2 (McCHS-2), chitinase (McCHI), and β-N-acetylglucosaminidase (McNAG) enzymes, involved in PM chitin metabolism, were also identified. McCHS-2 expression was specific to the midgut indicating that it is responsible for chitin synthesis in the PM, the only chitinous material in the midgut. In contrast, the genes encoding the chitinolytic enzymes were expressed in multiple tissues. McCHS-2, McCHI, and McNAG were expressed in the midgut of feeding larvae, and NAG activity was present in the PM. This information was used to generate an updated model of the lepidopteran PM architecture.

Sarcoptes scabiei: genomics to proteomics to biology

BACKGROUND

The common scabies mite, Sarcoptes scabiei is a cosmopolitan parasite of humans and other mammals. An annotated genome of Sarcoptes scabiei var. canis has been deposited in the National Center for Biotechnology Information (NCBI) and VectorBase and a proteomic analysis of proteins in extracts of mite bodies and eggs from this strain has been reported. Here we mined the data to identify predicted proteins that are known to be involved in specific biological processes in other animals.

RESULTS

We identified predicted proteins that are associated with immunomodulation of the host defense system, and biological processes of the mite including oxygen procurement and aerobic respiration, oxidative metabolism, sensory reception and locating a host, neuronal transmission, stressors (heat shock proteins), molting, movement, nutrient procurement and digestion, and excretion and water balance. We used these data to speculate that certain biological processes may occur in scabies mites.

CONCLUSION

This analysis helps understand the biology of Sarcoptes scabiei var. canis and adds to the data already available in NCBI and VectorBase.

Draft genome of the scabies mite

Background

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.

Methods

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.

Results

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.

Conclusion

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.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1198-2) contains supplementary material, which is available to authorized users.

Pseudoproteases: mechanisms and function

Catalytically inactive enzymes (also known as pseudoproteases, protease homologues or paralogues, non-peptidase homologues, non-enzymes and pseudoenzymes) have traditionally been hypothesized to act as regulators of their active homologues. However, those that have been characterized demonstrate that inactive enzymes have an extensive and expanding role in biological processes, including regulation, inhibition and immune modulation. With the emergence of each new genome, more inactive enzymes are being identified, and their abundance and potential as therapeutic targets has been realized. In the light of the growing interest in this emerging field the present review focuses on the classification, structure, function and mechanism of inactive enzymes. Examples of how inactivity is defined, how this is reflected in the structure, functions of inactive enzymes in biological processes and their mode of action are discussed.

Parasitic scabies mites and associated bacteria joining forces against host complement defence

Scabies is a ubiquitous and contagious skin disease caused by the parasitic mite Sarcoptes scabiei Epidemiological studies have identified scabies as a causative agent for secondary skin infections caused by Staphylococcus aureus and Streptococcus pyogenes. This is an important notion, as such bacterial infections can lead to serious downstream life-threatening complications. As the complement system is the first line of host defence that confronts invading pathogens, both the mite and bacteria produce a large array of molecules that inhibit the complement cascades. It is hypothesised that scabies mite complement inhibitors may play an important role in providing a favourable micro-environment for the establishment of secondary bacterial infections. This review aims to bring together the current literature on complement inhibition by scabies mites and bacteria associated with scabies and to discuss the proposed molecular link between scabies and bacterial co-infections.

Parasitic mites of medical and veterinary importance--is there a common research agenda?

There are an estimated 0.5-1 million mite species on earth. Among the many mites that are known to affect humans and animals, only a subset are parasitic but these can cause significant disease. We aim here to provide an overview of the most recent work in this field in order to identify common biological features of these parasites and to inform common strategies for future research. There is a critical need for diagnostic tools to allow for better surveillance and for drugs tailored specifically to the respective parasites. Multi-'omics' approaches represent a logical and timely strategy to identify the appropriate mite molecules. Recent advances in sequencing technology enable us to generate de novo genome sequence data, even from limited DNA resources. Consequently, the field of mite genomics has recently emerged and will now rapidly expand, which is a particular advantage for parasitic mites that cannot be cultured in vitro. Investigations of the microbiota associated with mites will elucidate the link between parasites and pathogens, and define the role of the mite in transmission and pathogenesis. The databases generated will provide the crucial knowledge essential to design novel diagnostic tools, control measures, prophylaxes, drugs and immunotherapies against the mites and associated secondary infections.

Scabies mite inactive serine proteases are potent inhibitors of the human complement lectin pathway

Scabies is an infectious skin disease caused by the mite Sarcoptes scabiei and has been classified as one of the six most prevalent epidermal parasitic skin diseases infecting populations living in poverty by the World Health Organisation. The role of the complement system, a pivotal component of human innate immunity, as an important defence against invading pathogens has been well documented and many parasites have an arsenal of anti-complement defences. We previously reported on a family of scabies mite proteolytically inactive serine protease paralogues (SMIPP-Ss) thought to be implicated in host defence evasion. We have since shown that two family members, SMIPP-S D1 and I1 have the ability to bind the human complement components C1q, mannose binding lectin (MBL) and properdin and are capable of inhibiting all three human complement pathways. This investigation focused on inhibition of the lectin pathway of complement activation as it is likely to be the primary pathway affecting scabies mites. Activation of the lectin pathway relies on the activation of MBL, and as SMIPP-S D1 and I1 have previously been shown to bind MBL, the nature of this interaction was examined using binding and mutagenesis studies. SMIPP-S D1 bound MBL in complex with MBL-associated serine proteases (MASPs) and released the MASP-2 enzyme from the complex. SMIPP-S I1 was also able to bind MBL in complex with MASPs, but MASP-1 and MASP-2 remained in the complex. Despite these differences in mechanism, both molecules inhibited activation of complement components downstream of MBL. Mutagenesis studies revealed that both SMIPP-Ss used an alternative site of the molecule from the residual active site region to inhibit the lectin pathway. We propose that SMIPP-Ss are potent lectin pathway inhibitors and that this mechanism represents an important tool in the immune evasion repertoire of the parasitic mite and a potential target for therapeutics.

Vaccine against scabies: necessity and possibility

Scabies is an infectious disease that is endemic in poorly resourced communities, and also common in industrialized countries. Although the disease, which is caused by infestation of Sarcoptes scabiei, is generally mild, the need for a vaccine against S. scabiei is proposed. The immunological mechanisms that control S. scabiei infection are discussed and the current status of scabies vaccine development reviewed. Future directions for scabies vaccine development are also addressed.

An aspartic protease of the scabies mite Sarcoptes scabiei is involved in the digestion of host skin and blood macromolecules

Background

Scabies is a disease of worldwide significance, causing considerable morbidity in both humans and other animals. The scabies mite Sarcoptes scabiei burrows into the skin of its host, obtaining nutrition from host skin and blood. Aspartic proteases mediate a range of diverse and essential physiological functions such as tissue invasion and migration, digestion, moulting and reproduction in a number of parasitic organisms. We investigated whether aspartic proteases may play role in scabies mite digestive processes.

Methodology/Principle Findings

We demonstrated the presence of aspartic protease activity in whole scabies mite extract. We then identified a scabies mite aspartic protease gene sequence and produced recombinant active enzyme. The recombinant scabies mite aspartic protease was capable of digesting human haemoglobin, serum albumin, fibrinogen and fibronectin, but not collagen III or laminin. This is consistent with the location of the scabies mites in the upper epidermis of human skin.

Conclusions/Significance

The development of novel therapeutics for scabies is of increasing importance given the evidence of emerging resistance to current treatments. We have shown that a scabies mite aspartic protease plays a role in the digestion of host skin and serum molecules, raising the possibility that interference with the function of the enzyme may impact on mite survival.

Scabies is an infectious disease of the skin caused by infestation with the parasitic mite Sarcoptes scabiei. It is a disease that has a considerable impact on humans and other animals, including livestock, wildlife and companion animals. Scabies mites burrow into the skin of their host, consuming host skin and blood molecules. Aspartic proteases play a key role in invasion and digestion processes in many parasitic organisms. We have identified a scabies mite aspartic protease and have shown that it is capable of digesting human haemoglobin, serum albumin, fibrinogen and fibronectin in vitro, indicating that it plays a role in mite digestive processes. This raises the possibility that interfering with the function of this digestive enzyme may impact on mite survival.

Characterization and evaluation of a Sarcoptes scabiei allergen as a candidate vaccine

Background

Sarcoptic mange caused by the mite Sarcoptes scabiei is a worldwide disease affecting both humans and animals. Here we report the molecular characterization and evaluation of a recombinant S. scabiei tropomyosin (SsTm) protein in a vaccination trial in rabbits.

Methods

The full-length cDNA was cloned in a bacterial pET vector, and the recombinant protein was expressed in BL21 (DE3) cells and purified. Using specific rabbit antiserum, tropomyosin was localized immunohistochemically in mite tissue sections. Vaccination trials with the recombiant SsTm was carried out in New Zealand rabbits.

Results

The full-length open reading frame (ORF) of the 852 bp cloned gene from S. scabiei encodes a 32.9 kDa protein. The amino acid sequence showed 98.94%, 97.89% and 98.59% homology to Dermatophagoides farina and Dermatophagoides pteronyssinus group 10 allergens and Psoroptes ovis tropomyosin, respectively. Tropomyosin was localized immunohistochemically in mite tissue sections mainly in the mouthparts, legs and integument of the epidermis. The predicted cross-reactivity of SsTm indicated that it is an allergenic protein. While vaccination with the recombiant SsTm resulted in high levels of specific IgG (P < 0.01), a low IgE antibody response and no significant protection against S. scabiei challenge were observed. After challenge, specific IgG levels remained significantly higher than the control (P < 0.01), while changes of total IgE levels were not significant (P > 0.05). However, the lesion areas in the vaccination group decreased at the end of the experiment compared with controls.

Conclusions

Although vaccination with recombinant SsTm did not efficiently control sarcoptic mange in rabbits, the immunogenic properties of tropomyosin suggest it may be developed as a vaccine with alternative adjuvants or delivery methods.

Scabies in the developing world--its prevalence, complications, and management

Scabies remains one of the commonest of skin diseases seen in developing countries. Although its distribution is subject to a cycle of infection, with peaks and troughs of disease prevalence, this periodicity is often less obvious in poor communities. Scabies is a condition that affects families, particularly the most vulnerable; it also has the greatest impact on young children. Largely through the association with secondary bacterial infection caused by group A streptococci and Staphylococcus aureus, the burden of disease is compounded by nephritis, rheumatic fever and sepsis in developing countries. However, with a few notable exceptions, it remains largely neglected as an important public health problem. The purpose of this review is to provide an update on the current position of scabies with regard to its complications and control in resource-poor countries.

Complement inhibitors from scabies mites promote streptococcal growth--a novel mechanism in infected epidermis?

Background

Scabies is highly prevalent in socially disadvantaged communities such as indigenous populations and in developing countries. Generalized itching causes discomfort to the patient; however, serious complications can occur as a result of secondary bacterial pyoderma, commonly caused by Streptococcus pyogenes (GAS) or Staphylococcus aureus. In the tropics, skin damage due to scabies mite infestations has been postulated to be an important link in the pathogenesis of disease associated with acute rheumatic fever and heart disease, poststreptococcal glomerulonephritis and systemic sepsis. Treatment of scabies decreases the prevalence of infections by bacteria. This study aims to identify the molecular mechanisms underlying the link between scabies and GAS infections.

Methodology/Principal Findings

GAS bacteria were pre-incubated with blood containing active complement, phagocytes and antibodies against the bacteria, and subsequently tested for viability by plate counts. Initial experiments were done with serum from an individual previously exposed to GAS with naturally acquired anti-GAS antibodies. The protocol was optimized for large-scale testing of low-opsonic whole blood from non-exposed human donors by supplementing with a standard dose of heat inactivated human sera previously exposed to GAS. This allowed an extension of the dataset to two additional donors and four proteins tested at a range of concentrations. Shown first is the effect of scabies mite complement inhibitors on human complement using ELISA-based complement activation assays. Six purified recombinant mite proteins tested at a concentration of 50 µg/ml blocked all three complement activation pathways. Further we demonstrate in human whole blood assays that each of four scabies mite complement inhibitors tested increased GAS survival rates by 2–15 fold.

Conclusions/Significance

We propose that local complement inhibition plays an important role in the development of pyoderma in scabies infested skin. This molecular link between scabies and bacterial infections may provide new avenues to develop alternative treatment options against this neglected disease.

Australian Aborigines experience streptococcal invasive diseases at a five times greater rate than the general Australian population [1], contributing to an estimated life expectancy gap of currently 13 years [2] with infectious diseases being the major cause in remote areas. Alternative approaches to control skin infection and associated complications in Aboriginal communities are imperative [3]. A clear link between scabies and bacterial pyoderma has been recognised as an underlying factor of Aboriginal cases of rheumatic fever and heart disease (RF/RHD), skin sepsis and renal disease [4]. Aiming to elucidate the causal molecular mechanisms we identified multiple scabies intestinal protein families functioning as inhibitors of human complement pathways, thereby preventing complement-mediated gut damage. The work presented here is at the forefront of a new agenda, looking at the interactions between scabies mites, bacteria and the host. We show that scabies mite proteins act as complement inhibitors and enhance GAS growth in whole blood assays, presumably by inhibition of host innate immunity. Based on this groundwork data we hypothesize that the complement-inhibitory functions of excreted gut molecules promote the growth of bacterial pathogens in the microenvironment of the epidermal burrows.

Novel scabies mite serpins inhibit the three pathways of the human complement system

Scabies is a parasitic infestation of the skin by the mite Sarcoptes scabiei that causes significant morbidity worldwide, in particular within socially disadvantaged populations. In order to identify mechanisms that enable the scabies mite to evade human immune defenses, we have studied molecules associated with proteolytic systems in the mite, including two novel scabies mite serine protease inhibitors (SMSs) of the serpin superfamily. Immunohistochemical studies revealed that within mite-infected human skin SMSB4 (54 kDa) and SMSB3 (47 kDa) were both localized in the mite gut and feces. Recombinant purified SMSB3 and SMSB4 did not inhibit mite serine and cysteine proteases, but did inhibit mammalian serine proteases, such as chymotrypsin, albeit inefficiently. Detailed functional analysis revealed that both serpins interfered with all three pathways of the human complement system at different stages of their activation. SMSB4 inhibited mostly the initial and progressing steps of the cascades, while SMSB3 showed the strongest effects at the C9 level in the terminal pathway. Additive effects of both serpins were shown at the C9 level in the lectin pathway. Both SMSs were able to interfere with complement factors without protease function. A range of binding assays showed direct binding between SMSB4 and seven complement proteins (C1, properdin, MBL, C4, C3, C6 and C8), while significant binding of SMSB3 occurred exclusively to complement factors without protease function (C4, C3, C8). Direct binding was observed between SMSB4 and the complement proteases C1s and C1r. However no complex formation was observed between either mite serpin and the complement serine proteases C1r, C1s, MASP-1, MASP-2 and MASP-3. No catalytic inhibition by either serpin was observed for any of these enzymes. In summary, the SMSs were acting at several levels mediating overall inhibition of the complement system and thus we propose that they may protect scabies mites from complement-mediated gut damage.

Quantitative PCR-based genome size estimation of the astigmatid mites Sarcoptes scabiei, Psoroptes ovis and Dermatophagoides pteronyssinus

Background

The lack of genomic data available for mites limits our understanding of their biology. Evolving high-throughput sequencing technologies promise to deliver rapid advances in this area, however, estimates of genome size are initially required to ensure sufficient coverage.

Methods

Quantitative real-time PCR was used to estimate the genome sizes of the burrowing ectoparasitic mite Sarcoptes scabiei, the non-burrowing ectoparasitic mite Psoroptes ovis, and the free-living house dust mite Dermatophagoides pteronyssinus. Additionally, the chromosome number of S. scabiei was determined by chromosomal spreads of embryonic cells derived from single eggs.

Results

S. scabiei cells were shown to contain 17 or 18 small (< 2 μM) chromosomes, suggesting an XO sex-determination mechanism. The average estimated genome sizes of S. scabiei and P. ovis were 96 (± 7) Mb and 86 (± 2) Mb respectively, among the smallest arthropod genomes reported to date. The D. pteronyssinus genome was estimated to be larger than its parasitic counterparts, at 151 Mb in female mites and 218 Mb in male mites.

Conclusions

This data provides a starting point for understanding the genetic organisation and evolution of these astigmatid mites, informing future sequencing projects. A comparitive genomic approach including these three closely related mites is likely to reveal key insights on mite biology, parasitic adaptations and immune evasion.

Scabies: important clinical consequences explained by new molecular studies

In 2004, we reviewed the status of disease caused by the scabies mite Sarcoptes scabiei at the time and pointed out that very little basic research had ever been done. The reason for this was largely the lack of availability of mites for experimental purposes and, to a degree, a consequent lack of understanding of its importance, resulting in the trivial name 'itch mite'. Scabies is responsible for major morbidity in disadvantaged communities and immunocompromised patients worldwide. In addition to the physical discomfort caused by the disease, scabies infestations facilitate infection by bacterial pathogens such as Streptococcus pyogenes and Staphylococcus aureus via skin lesions, resulting in severe downstream disease such as in a high prevalence of rheumatic fever/heart disease in affected communities. We now have further evidence that in disadvantaged populations living in tropical climates, scabies rather than 'Strep throat' is an important source of S. pyogenes causing rheumatic fever and eventually rheumatic heart disease. In addition, our work has resulted in two fundamental research tools that facilitate much of the current biomedical research efforts on scabies, namely a public database containing ~45,000 scabies mite expressed sequence tags and a porcine in vivo model. Here we will discuss novel and unexpected proteins encountered in the database that appear crucial to mite survival with regard to digestion and evasion of host defence. The mode(s) of action of some of these have been at least partially revealed. Further, newly discovered molecules that may well have a similar role, such as a family of inactivated cysteine proteases, are yet to be investigated. Hence, there are now whole families of potential targets for chemical inhibitors of S. scabiei. These efforts put today's scabies research in a unique position to design and test small molecules that may specifically interfere with mite-derived molecules, such as digestive proteases and mite complement inhibitors. The porcine scabies model will be available to trial in vivo treatment with potential inhibitors. New therapies for scabies may be developed from these studies and may contribute to reduce the spread of scabies and the subsequent prevalence of bacterial skin infections and their devastating sequelae in the community.

Scabies mite peritrophins are potential targets of human host innate immunity

BACKGROUND

Pruritic scabies lesions caused by Sarcoptes scabiei burrowing in the stratum corneum of human skin facilitate opportunistic bacterial infections. Emerging resistance to current therapeutics emphasizes the need to identify novel targets for protective intervention. We have characterized several protein families located in the mite gut as crucial factors for host-parasite interactions. Among these multiple proteins inhibit human complement, presumably to avoid complement-mediated damage of gut epithelial cells. Peritrophins are major components of the peritrophic matrix often found in the gut of arthropods. We hypothesized that a peritrophin, if abundant in the scabies mite gut, could be an activator of complement.

METHODOLOGY/PRINCIPAL FINDINGS

A novel full length scabies mite peritrophin (SsPTP1) was identified in a cDNA library from scabies mites. The amino acid sequence revealed four putative chitin binding domains (CBD). Recombinant expression of one CBD of the highly repetitive SsPTP1 sequence as TSP-hexaHis-fusion protein resulted in soluble protein, which demonstrated chitin binding activity in affinity chromatography assays. Antibodies against a recombinant SsPTP1 fragment were used to immunohistochemically localize native SsPTP1 in the mite gut and in fecal pellets within the upper epidermis, co-localizing with serum components such as host IgG and complement. Enzymatic deglycosylation confirmed strong N- and O-glycosylation of the native peritrophin. Serum incubation followed by immunoblotting with a monoclonal antibody against mannan binding lectin (MBL), the recognition molecule of the lectin pathway of human complement activation, indicated that MBL may specifically bind to glycosylated SsPTP1.

CONCLUSIONS/SIGNIFICANCE

This study adds a new aspect to the accumulating evidence that complement plays a major role in scabies mite biology. It identifies a novel peritrophin localized in the mite gut as a potential target of the lectin pathway of the complement cascade. These initial findings indicate a novel role of scabies mite peritrophins in triggering a host innate immune response within the mite gut.

Sarcoptes-World Molecular Network (Sarcoptes-WMN): integrating research on scabies

Parasites threaten human and animal health globally. It is estimated that more than 60% of people on planet Earth carry at least one parasite, many of them several different species. Unfortunately, parasite studies suffer from duplications and inconsistencies between different investigator groups. Hence, groups need to collaborate in an integrated manner in areas including parasite control, improved therapy strategies, diagnostic and surveillance tools, and public awareness. Parasite studies will be better served if there is coordinated management of field data and samples across multidisciplinary approach plans, among academic and non-academic organizations worldwide. In this paper we report the first 'Living organism-World Molecular Network', with the cooperation of 167 parasitologists from 88 countries on all continents. This integrative approach, the 'Sarcoptes-World Molecular Network', seeks to harmonize Sarcoptes epidemiology, diagnosis, treatment, and molecular studies from all over the world, with the aim of decreasing mite infestations in humans and animals.

Monoclonal antibodies against recombinant Der f 3 reveal localization of Der f 3 in the gut and faecal pellets of Dermatophagoides farinae

Home dust mite derived materials are known to be a major source of problematic inhalant allergens. The aim of this study was to determine the localization of the group 3 allergen, Der f 3, within Dermatophagoides farinae, in order to assess the relative importance of excreted materials and nonexcreted body components as allergen sources. Recombinant Der f 3 (rDer f 3) was expressed in bacteria and purified as an immunogen for production of monoclonal antibodies (mAb) against it. Dermatophagoides farinae mites and their faecal pellets were embedded in paraffin, and serial sections were immunoprobed with mAb clone 3D3 against Der f 3. D. farinae midgut mucosa, gut contents and faecal pellets were strongly immunopositive for Der f 3. Der f 3 immunoreactive products were not detected in any other internal organs of the mite. These results suggest that Der f 3 allergen may be synthesized in and secreted from the digestive tract and excreted from the mite's body in the faecal pellets.

A tractable experimental model for study of human and animal scabies

BACKGROUND

Scabies is a parasitic skin infestation caused by the burrowing mite Sarcoptes scabiei. It is common worldwide and spreads rapidly under crowded conditions, such as those found in socially disadvantaged communities of Indigenous populations and in developing countries. Pruritic scabies lesions facilitate opportunistic bacterial infections, particularly Group A streptococci. Streptococcal infections cause significant sequelae and the increased community streptococcal burden has led to extreme levels of acute rheumatic fever and rheumatic heart disease in Australia's Indigenous communities. In addition, emerging resistance to currently available therapeutics emphasizes the need to identify potential targets for novel chemotherapeutic and/or immunological intervention. Scabies research has been severely limited by the availability of parasites, and scabies remains a truly neglected infectious disease. We report development of a tractable model for scabies in the pig, Sus domestica.

METHODOLOGY/PRINCIPAL FINDINGS

Over five years and involving ten independent cohorts, we have developed a protocol for continuous passage of Sarcoptes scabiei var. suis. To increase intensity and duration of infestation without generating animal welfare issues we have optimised an immunosuppression regimen utilising daily oral treatment with 0.2 mg/kg dexamethasone. Only mild, controlled side effects are observed, and mange infection can be maintained indefinitely providing large mite numbers (> 6000 mites/g skin) for molecular-based research on scabies. In pilot experiments we explore whether any adaptation of the mite population is reflected in genetic changes. Phylogenetic analysis was performed comparing sets of genetic data obtained from pig mites collected from naturally infected pigs with data from pig mites collected from the most recent cohort.

CONCLUSIONS/SIGNIFICANCE

A reliable pig/scabies animal model will facilitate in vivo studies on host immune responses to scabies including the relations to the associated bacterial pathogenesis and more detailed studies of molecular evolution and host adaptation. It is a most needed tool for the further investigation of this important and widespread parasitic disease.

Increased allergic immune response to Sarcoptes scabiei antigens in crusted versus ordinary scabies

Scabies, a parasitic skin infestation by the burrowing "itch" mite Sarcoptes scabiei, causes significant health problems for children and adults worldwide. Crusted scabies is a particularly severe form of scabies in which mites multiply into the millions, causing extensive skin crusting. The symptoms and signs of scabies suggest host immunity to the scabies mite, but the specific resistant response in humans remains largely uncharacterized. We used 4 scabies mite recombinant proteins with sequence homology to extensively studied house dust mite allergens to investigate a differential immune response between ordinary scabies and the debilitating crusted form of the disease. Subjects with either disease form showed serum IgE against recombinant S. scabiei cysteine and serine proteases and apolipoprotein, whereas naive subjects showed minimal IgE reactivity. Significantly (P < 0.05) greater serum IgE and IgG4 binding to mite apolipoprotein occurred in subjects with crusted scabies than in those with ordinary scabies. Both subject groups showed strong proliferative responses (peripheral blood mononuclear cells) to the scabies antigens, but the crusted scabies group showed increased secretion of the Th2 cytokines interleukin 5 (IL-5) and IL-13 and decreased Th1 cytokine gamma interferon (IFN-gamma) in response to the active cysteine protease. These data confirm that a nonprotective allergic response occurs in the crusted disease form and demonstrate that clinical severity is associated with differences in the type and magnitude of the antibody and cellular responses to scabies proteins. A quantitative IgE inhibition assay identified IgE immunoreactivity of scabies mite antigens distinct from that of house dust mite antigens, which is potentially important for specific scabies diagnosis and therapy.

The effect of diet on the expression of lipase genes in the midgut of the lightbrown apple moth (Epiphyas postvittana Walker; Tortricidae)

We have identified lipase-like genes from an Epiphyas postvittana larval midgut EST library. Of the 10 pancreatic lipase family genes, six appear to encode active lipases and four encode inactive lipases, based on the presence/absence of essential catalytic residues. The four gastric lipase family genes appear to encode active proteins. Phylogenetic analysis of 54 lepidopteran pancreatic lipase proteins resolved the clade into five groups of midgut origin and a sixth of non-midgut lipases. The inactive proteins formed two separate groups with highly conserved mutations. The lepidopteran midgut lipases formed a ninth subfamily of pancreatic lipases. Eighteen insect and human gastric lipases were analysed phylogenetically with only very weak support for any groupings. Gene expression was measured in the larval midgut following feeding on five artificial diets and on apple leaves. The artificial diets contained different levels of triacylglycerol, linoleic acid and cholesterol. Significant changes in gene expression (more than 100-fold for active pancreatic lipases) were observed. All the inactive lipases were also highly expressed. The gastric lipase genes were expressed at lower levels and suppressed in larvae feeding on leaves. Together, protein motif analysis and the gene expression data suggest that, in phytophagous lepidopteran larvae, the pancreatic lipases may function in vivo as galactolipases and phospholipases whereas the gastric lipases may function as triacylglycerol hydrolases.

Characterization of a serine protease homologous to house dust mite group 3 allergens from the scabies mite Sarcoptes scabiei

The scabies mite, Sarcoptes scabiei var. hominis, infests human skin, causing allergic reactions and facilitating bacterial infection by Streptococcus sp., with serious consequences such as rheumatic fever and rheumatic heart disease. To identify a possible drug target or vaccine candidate protein, we searched for homologues of the group 3 allergen of house dust mites, which we subsequently identified in a cDNA library. The native protein, designated Sar s 3, was shown to be present in the mite gut and excreted in fecal pellets into mite burrows within the upper epidermis. The substrate specificity of proteolytically active recombinant rSar s 3 was elucidated by screening a bacteriophage library. A preference for substrates containing a RS(G/A) sequence at the P1-P2' positions was revealed. A series of peptides synthesized as internally quenched fluorescent substrates validated the phage display data and high performance liquid chromatography/mass spectrometry analysis of the preferred cleaved substrate and confirmed the predicted cleavage site. Searches of the human proteome using sequence data from the phage display allowed the in silico prediction of putative physiological substrates. Among these were numerous epidermal proteins, with filaggrin being a particularly likely candidate substrate. We showed that recombinant rSar s 3 cleaves human filaggrin in vitro and obtained immunohistological evidence that the filaggrin protein is ingested by the mite. This is the first report elucidating the substrate specificity of Sar s 3 and its potential role in scabies mite biology.

Scabies mite inactivated serine protease paralogs inhibit the human complement system

Infestation of skin by the parasitic itch mite Sarcoptes scabiei afflicts 300 million people worldwide and there is a need for novel and efficient therapies. We have previously identified a multigene family of serine proteases comprising multiple catalytically inactive members (scabies mite-inactivated protease paralogs (SMIPPs)), which are secreted into the gut of S. scabiei. SMIPPs are located in the mite gut and in feces excreted into the upper epidermis. Scabies mites feed on epidermal protein, including host plasma; consequently, they are exposed to host defense mechanisms both internally and externally. We found that two recombinantly expressed SMIPPs inhibited all three pathways of the human complement system. Both SMIPPs exerted their inhibitory action due to binding of three molecules involved in the three different mechanisms which initiate complement: C1q, mannose-binding lectin, and properdin. Both SMIPPs bound to the stalk domains of C1q, possibly displacing or inhibiting C1r/C1s, which are associated with the same domain. Furthermore, we found that binding of both SMIPPs to properdin resulted in prevention of assembly of the alternative pathway convertases. However, the SMIPPs were not able to dissociate already formed convertases. Immunohistochemical staining demonstrated the presence of C1q in the gut of scabies mites in skin burrows. We propose that SMIPPs minimize complement-mediated gut damage and thus create a favorable environment for the scabies mites.

Structural mechanisms of inactivation in scabies mite serine protease paralogues

The scabies mite (Sarcoptes scabiei) is a parasite responsible for major morbidity in disadvantaged communities and immuno-compromised patients worldwide. In addition to the physical discomfort caused by the disease, scabies infestations facilitate infection by Streptococcal species via skin lesions, resulting in a high prevalence of rheumatic fever/heart disease in affected communities. The scabies mite produces 33 proteins that are closely related to those in the dust mite group 3 allergen and belong to the S1-like protease family (chymotrypsin-like). However, all but one of these molecules contain mutations in the conserved active-site catalytic triad that are predicted to render them catalytically inactive. These molecules are thus termed scabies mite inactivated protease paralogues (SMIPPs). The precise function of SMIPPs is unclear; however, it has been suggested that these proteins might function by binding and protecting target substrates from cleavage by host immune proteases, thus preventing the host from mounting an effective immune challenge. In order to begin to understand the structural basis for SMIPP function, we solved the crystal structures of SMIPP-S-I1 and SMIPP-S-D1 at 1.85 A and 2.0 A resolution, respectively. Both structures adopt the characteristic serine protease fold, albeit with large structural variations over much of the molecule. In both structures, mutations in the catalytic triad together with occlusion of the S1 subsite by a conserved Tyr200 residue is predicted to block substrate ingress. Accordingly, we show that both proteases lack catalytic function. Attempts to restore function (via site-directed mutagenesis of catalytic residues as well as Tyr200) were unsuccessful. Taken together, these data suggest that SMIPPs have lost the ability to bind substrates in a classical "canonical" fashion, and instead have evolved alternative functions in the lifecycle of the scabies mite.

Immunization of proteins from Toxascaris leonina adult worm inhibits allergic specific Th2 response

Recently, the influence of parasitic infections on the incidence of allergic diseases has become the focus of increased attention. In order to ascertain whether parasite-derived proteins could inhibit the allergic specific Th2 response, we applied excretory-secretory protein (Tl-ES) or total protein (Tl-TP) of the adult worm Toxascaris leonina to asthma model mice prior to or simultaneously with OVA challenge, after which we assessed the OVA-specific Th2 responses. The group subjected to immunization with Tl-ES and Tl-TP (immunized group) evidenced a thinning of the bronchial epithelial and muscle layer, a disruption and shedding of epithelial cells, a reduction in the number of goblet cells, and a reduction in mucus production as compared to the group treated with Tl-ES coupled with OVA challenge (challenge with OVA groups) and the OVA-induced asthma group. The administration of Tl-ES and Tl-TP, regardless of injection time, was shown to inhibit the recruitment of inflammatory cells into the airway, and in particular, macrophages, neutrophils, and lymphocytes were significantly reduced as the result of the parasite proteins. However, the total number of eosinophils was slightly reduced as the result of the administration of parasite proteins. Sensitization and OVA challenge was shown to accelerate the secretion of Th2 cytokines (IL-4 and IL-5) within the lung, but in the immunized groups, those levels were lower. The administration of Tl-TP and OVA challenge group also evidenced a significant reduction in IL-4 levels as compared to the OVA-challenged group. The concentrations of Th2 cytokines in the Tl-ES and OVA challenge group were more similar to those observed in the OVA-challenged group. The concentration of IL-10 and TGF-beta in the lung was decreased substantially in the OVA-only challenge group, but the Tl-TP immunized group exhibited significantly induced IL-10 cytokine. OVA-specific IgG2a, IgG1, and IgE levels in the immunized groups were significantly lower than those detected in the OVA-challenged group. In conclusion, parasite-derived protein is able to inhibit OVA-specific Th2 responses, and in particular, immunization with parasite proteins exerts a more profound protective effect than is seen with the treatment of allergic reactions. The results of our study are encouraging in terms of our further understanding of the molecular basis of immune evasion by nematodes.

Serine proteases identified from a Costelytra zealandica (White) (Coleoptera: Scarabaeidae) midgut EST library and their expression through insect development

Costelytra zealandica larvae are pests of New Zealand pastures causing damage by feeding on the roots of grasses and clovers. The major larval protein digestive enzymes are serine proteases (SPs), which are targets for disruption in pest control. An expressed sequence tag (EST) library from healthy, third instar larval midgut tissue was constructed and analysed to determine the composition and regulation of proteases in the C. zealandica larval midgut. Gene mining identified three trypsin-like and 11 chymotrypsin-like SPs spread among four major subgroups. Representative SPs were examined by quantitative PCR and enzyme activity assayed across developmental stages. The serine protease genes examined were expressed throughout feeding stages and downregulated in nonfeeding stages. The study will improve targeting of protease inhibitors and bacterial disruptors of SP synthesis.

Characterisation of recombinant immunoreactive antigens of the scab mite Sarcoptes scabiei

Sarcoptic mange (or scabies) is an important skin disease which can affect a variety of species including humans, cattle, goats, sheep, horses, pigs, rabbits, and dogs. Approximately 300 million people are affected worldwide and in lifestock animals the infestation may lead to substantial economic losses caused by depression in growth and feed conversion rates. Diagnosis of Sarcoptes infestation is difficult and only a few serological tests have been developed using whole mite antigen for diagnosis of mange in animals. Here we describe the isolation and characterisation of cDNAs of several immunoreactive clones and their recombinant expression in Escherichia coli. Three of the proteins contain repetitive sequences which suggests that they might be involved in immune evasion. The application of these antigens in serodiagnosis and the suitability for diagnosis is discussed.