Vaccine against scabies: necessity and possibility

Evidence underscoring immunological and clinical pathological changes associated with Sarcoptes scabiei infection: synthesis and meta-analysis

BACKGROUND

Sarcoptes scabiei is one of the most impactful mammalian parasites. There has been much research on immunological and clinical pathological changes associated with S. scabiei parasitism across a range of host species. This rich body of literature is complex, and we seek to bring that complexity together in this study. We first (1) synthesise narrative reviews of immunopathological relationships to S. scabiei infection to construct overarching hypotheses; then (2) undertake a systematic meta-analysis of primary literature on immunological and clinical pathological changes; and lastly (3) contrast our findings from the meta-analysis to our synthesis from narrative reviews.

METHODS

We synthesised 55 narrative reviews into two overarching hypotheses representing type I and type IV immune responses to S. scabiei infection. We then systematically extracted all literature reporting immunological variables, acute phase proteins, oxidant/antioxidant status, and erythrocytic, hepatological and nephrological changes, calculating 565 effect sizes between controls and sarcoptic mange affected groupings, refining (simplifying) hypotheses from narrative reviews.

RESULTS

Immunological and clinical pathological parameters were most often studied in dogs (n = 12) and humans (n = 14). Combining immunological and clinical pathological information across mammalian species (n = 19) helped yield general insights into observed disease responses. This is evidenced by interspecific consensus in 27 immunological and clinical pathology variables (6/26 type I hypersensitivity, 3/20 type IV hypersensitivity, 6/10 oxidant/antioxidant status, 3/6 acute phase protein, 4/7 erythrocytic, and 5/10 hepatological/nephrological).

CONCLUSIONS

Elevated IgE, eosinophils and mast cells in type I hypersensitivity response corresponded to what was described in narrative reviews. Results from type IV hypersensitivity response suggested typical antibody response, however cell-mediated response was less evident. Some consensus of acute phase protein response and shifted oxidant/antioxidant balance and slight evidence of anemia. We highlight the need for mange/scabies studies to more routinely compare immunological and clinical pathological changes against controls, and include collection of a more standardised suite of variables among studies.

Mange in Rabbits: An Ectoparasitic Disease with a Zoonotic Potential

Mange in rabbits is a very important parasitic disease causing high losses. The disease is caused mainly by Sarcoptes scabiei, Psoroptes cuniculi, Cheyletiella parasitovorax, and Notoedres cati. Body mange and ear mange are the most common forms of this disease in rabbits. Animals can get mite infestation through direct contact with infected animals or contaminated fomites. This infestation is characterized by zoonotic nature and public health burden. The skin affection is characterized by pruritus, alopecia, severe cachexia, and sometimes death. Infestation is diagnosed mainly by skin scraping and microscopic examination. Control measures mainly depend on the use of different types of systemic and topical acaricides and the use of natural products and supportive elements. Vaccine is not commercially available and is still under investigation. Accordingly, this review article was designed to shed the light on the mange disease in rabbits in terms of mite's infestation and susceptibility, clinical manifestations, zoonosis, diagnosis, and control strategies.

Natural-Product-Based Solutions for Tropical Infectious Diseases

About half of the world's population and 80% of the world's biodiversity can be found in the tropics. Many diseases are specific to the tropics, with at least 41 diseases caused by endemic bacteria, viruses, parasites, and fungi. Such diseases are of increasing concern, as the geographic range of tropical diseases is expanding due to climate change, urbanization, change in agricultural practices, deforestation, and loss of biodiversity. While traditional medicines have been used for centuries in the treatment of tropical diseases, the active natural compounds within these medicines remain largely unknown. In this review, we describe infectious diseases specific to the tropics, including their causative pathogens, modes of transmission, recent major outbreaks, and geographic locations. We further review current treatments for these tropical diseases, carefully consider the biodiscovery potential of the tropical biome, and discuss a range of technologies being used for drug development from natural resources. We provide a list of natural products with antimicrobial activity, detailing the source organisms and their effectiveness as treatment. We discuss how technological advancements, such as next-generation sequencing, are driving high-throughput natural product screening pipelines to identify compounds with therapeutic properties. This review demonstrates the impact natural products from the vast tropical biome have in the treatment of tropical infectious diseases and how high-throughput technical capacity will accelerate this discovery process.

Scabies: Epidemiology, Diagnosis, and Treatment

BACKGROUND

Scabies is a skin infestation whose incidence is apparently rising.

METHODS

This review is based on pertinent articles retrieved by a selective search of PubMed on diagnosis and treatment strategies.

RESULTS

Thread-like papules (burrows), new, intense pruritus, and dermatitis guide the suspected diagnosis which is confirmed by the microscopic or dermatoscopic demonstration of scabies mites. The first line therapy is topical application of permethrin, in accordance with the current recommendations for its use. Other treatment options include systemic ivermectin and topical crotamiton or benzyl benzoate. A combination of permethrin and ivermectin is used to treat otherwise intractable cases and is generally indicated for the treatment of crusted scabies. Known causes of treatment failure include improper application of the external agents, failure of repeated treatment with ivermectin, incomplete decontamination of furnishings and clothes, failure to simultaneously treat contact persons, absence of written documents explaining treatment modalities, and the patient's belonging to a risk group. Even though there has not yet been any direct proof of resistance of scabies mites to permethrin, there is a rising number of welldocumented cases of poor response to this agent. Moxidectin is a new substance now undergoing clinical testing.

CONCLUSION

Treatment of scabies according to the guidelines and the additional recommendations reported here should result in effective curing, even in cases that are thought to be intractable.

Scabies as a part of the World Health Organization roadmap for neglected tropical diseases 2021-2030: what we know and what we need to do for global control

Background

Scabies is an under-recognized global health problem with an unacceptably high prevalence in many settings worldwide. Fortunately, the World Health Organization (WHO) has formally designated scabies as a neglected tropical disease in 2017, in the hope of increasing awareness and encouraging efforts to eradicate it. Also, scabies has recently been included as part of the WHO roadmap for neglected tropical diseases 2021–2030, aimed at ending the neglect to attain the Sustainable Development Goals.

Main abstract body

This review article places scabies in focus. The literature was reviewed to explore discussions on controversial issues in scabies control, with the aim of clarifying whether global control of scabies is a feasible and worthwhile objective. The existing status of scabies and its burden are discussed along with future prospects for its global control. The article investigates the feasibility of scabies control and provides updates on the various impediments to this goal, such as challenges related to transmission, diagnosis, treatment, and vaccine development. Also examined are relevant research needs, success factors, and reasons for failure. This article aims to increase the global awareness of scabies and promote discussion, enhance coordinated international efforts, and ultimately, enact change at the national and worldwide levels toward the control of this preventable disease of the poor.

Conclusion

Despite the current challenges, scabies control is now within reach. With sustained interventions, continuous resources, and sincere commitment and support, scabies global control appears to be a worthwhile, realistic goal that is potentially achievable in the not so distant future.

Sarcoptes Infestation. What Is Already Known, and What Is New about Scabies at the Beginning of the Third Decade of the 21st Century?

Currently, there are three known subtypes of scabies: ordinary, crusted, and bullous. The worldwide prevalence of scabies remains high in the 21st century. To decrease the social, economic, and psychological impact on the enormous population infected, a lot of important work has been completed over the last 20 years concerning the management of scabies. For example, a standardization of guidelines for the treatment of scabies has been completed and programs have been designed for the prevention and treatment in endemic populations, called mass drug administrations. Unfortunately, these only apply to the ordinary form of scabies. Moreover, resistance to the drugs currently used in treatment is growing, which imposes the need to search for new treatments. For this purpose, new acaricides are being developed to enhance the therapeutic options for the patients' benefit and effectively treat this disease. There is also the necessity for prevention before the development of scabies. An effective vaccine has the potential to protect people before this disease, especially in endemic areas. Unfortunately, there are no such vaccines against Sarcoptes yet.

High-quality nuclear genome for Sarcoptes scabiei-A critical resource for a neglected parasite

The parasitic mite Sarcoptes scabiei is an economically highly significant parasite of the skin of humans and animals worldwide. In humans, this mite causes a neglected tropical disease (NTD), called scabies. This disease results in major morbidity, disability, stigma and poverty globally and is often associated with secondary bacterial infections. Currently, anti-scabies treatments are not sufficiently effective, resistance to them is emerging and no vaccine is available. Here, we report the first high-quality genome and transcriptomic data for S. scabiei. The genome is 56.6 Mb in size, has a a repeat content of 10.6% and codes for 9,174 proteins. We explored key molecules involved in development, reproduction, host-parasite interactions, immunity and disease. The enhanced 'omic data sets for S. scabiei represent comprehensive and critical resources for genetic, functional genomic, metabolomic, phylogenetic, ecological and/or epidemiological investigations, and will underpin the design and development of new treatments, vaccines and/or diagnostic tests.

Scabies: A comprehensive review and current perspectives

Human scabies is a contagious skin infestation caused by the parasitic mite Sarcoptes scabiei var. hominis. It is a common skin disease worldwide that occurs not only in the underprivileged sections of society but also in developed countries. In 2009, World Health Organization (WHO) recognized scabies as "neglected tropical disease (NTD)" or NTD thus emphasizing the need for community awareness and proper treatment strategies. This review attempts to summarize the varied clinical presentation of the disease and describes the advances in diagnosis and management including the ongoing search for novel agents to overcome the problems associated with conventional treatments. The literature research includes peer-reviewed articles (clinical trials or scientific reviews). Studies were identified by searching electronic databases (MEDLINE and PubMed) till February 2020 and reference lists of respective articles. Only articles published in English language were included.

An Antibody Persistent and Protective Two rSsCLP-Based Subunit Cocktail Vaccine against Sarcoptes scabiei in a Rabbit Model

Scabies is a highly contagious disease caused by Sarcoptes scabiei which burrows into stratum corneum of host's skin. In this study, after optimizing vaccination schedule, a vaccination trial is comprised of three test groups of rabbits (n = 10/group) by immunization with (1) rSsCLP5; (2) rSsCLP12; or (3) a mixture of rSsCLP5 and rSsCLP12, three biological replicates groups (n = 10/group) and three control groups (n = 10/group). Levels of specific IgG, total IgE and cytokines in sera were detected and histopathologically analyzed as indicators of vaccine effects. The results showed that 85% (17/20) of rabbits exhibited no detectable skin lesions of S. scabiei infestation in mixed protein groups compared to single protein groups with 75% (15/20) and 70% (14/20), respectively. Moreover, the deworming rates of mixed groups are increased by 10%-20% compared with that of single groups. Each of six groups immunized with rSsCLP displayed significant increases of specific IgG, total IgE, IL-10, and TNF-α. The degree of skin damage in test groups also significantly lower than that of control groups. Thus, purified rSsCLP5 and rSsCLP12 subunit cocktail vaccine induced robust immune protection and could significantly decrease mite populations to reduce the direct transmission between rabbits.

The Challenge of Developing a Single-Dose Treatment for Scabies

Scabies is a common skin disease with an estimated worldwide incidence of 200 million people infected per year. Its morbidity and mortality is principally due to secondary bacterial infections, a link now well recognized and prompting the recent inclusion of this disease-complex in the WHO list of neglected tropical diseases. The few treatments available are poorly effective against Sarcoptes scabiei eggs and appear to induce resistance in the parasite. An ideal alternative would be a single-dose regimen that kills all developmental stages, including eggs. Drugs used in the veterinary field and applied to other arthropods could be tested experimentally in an established pig-scabies model. Moreover, functional genomics combined with target validation through biochemical research should assist in identifying new drugs.

The public health control of scabies: priorities for research and action

Scabies is a parasitic disease of the skin that disproportionately affects disadvantaged populations. The disease causes considerable morbidity and leads to severe bacterial infection and immune-mediated disease. Scientific advances from the past 5 years suggest that scabies is amenable to population-level control, particularly through mass drug administration. In recognition of these issues, WHO added scabies to the list of neglected tropical diseases in 2017. To develop a global control programme, key operational research questions must now be addressed. Standardised approaches to diagnosis and methods for mapping are required to further understand the burden of disease. The safety of treatments for young children, including with ivermectin and moxidectin, should be investigated. Studies are needed to inform optimum implementation of mass treatment, including the threshold for intervention, target, dosing, and frequency. Frameworks for surveillance, monitoring, and evaluation of control strategies are also necessary.

Infected with Scabies Again? Focus in Management in Long-Term Care Facilities

Scabies is a significant public health condition in long-term care facilities, plaguing even developed countries. Although treatments are available, eradication and control of scabies cases still remain a challenge due to delays in diagnosis and difficulties in maintaining preventive and surveillance measures. Prompt treatment of patients and their contacts that are affected, along with concomitant education of health staff and family members, are paramount. Environmental disinfestation is also a concern.

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.

Metazoan Parasite Vaccines: Present Status and Future Prospects

Eukaryotic parasites and pathogens continue to cause some of the most detrimental and difficult to treat diseases (or disease states) in both humans and animals, while also continuously expanding into non-endemic countries. Combined with the ever growing number of reports on drug-resistance and the lack of effective treatment programs for many metazoan diseases, the impact that these organisms will have on quality of life remain a global challenge. Vaccination as an effective prophylactic treatment has been demonstrated for well over 200 years for bacterial and viral diseases. From the earliest variolation procedures to the cutting edge technologies employed today, many protective preparations have been successfully developed for use in both medical and veterinary applications. In spite of the successes of these applications in the discovery of subunit vaccines against prokaryotic pathogens, not many targets have been successfully developed into vaccines directed against metazoan parasites. With the current increase in -omics technologies and metadata for eukaryotic parasites, target discovery for vaccine development can be expedited. However, a good understanding of the host/vector/pathogen interface is needed to understand the underlying biological, biochemical and immunological components that will confer a protective response in the host animal. Therefore, systems biology is rapidly coming of age in the pursuit of effective parasite vaccines. Despite the difficulties, a number of approaches have been developed and applied to parasitic helminths and arthropods. This review will focus on key aspects of vaccine development that require attention in the battle against these metazoan parasites, as well as successes in the field of vaccine development for helminthiases and ectoparasites. Lastly, we propose future direction of applying successes in pursuit of next generation vaccines.

Scabies in the age of increasing drug resistance

Scabies is an infestation of the skin by the mite Sarcoptes scabiei. It manifests with pruritic erythematous papules and excoriations, in addition to the pathognomonic burrows. Multiple drugs can be used for treatment, but resistance to conventional therapy is increasing throughout the years. This paper will review the mechanisms of resistance proposed in the literature and some of the potential solutions to this problem.

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.

Molecular characteristics and serodiagnostic potential of chitinase-like protein from Sarcoptes scabiei

Scabies, caused by the mite Sarcoptes scabiei, is an allergic skin disease that affects millions of people and other mammals worldwide. This highly contagious parasitic disease is among the top 50 epidemic disease and is regarded as a neglected tropical disease. Diagnosis of scabies is difficult in the early stage, and the pathogenesis of scabies is not currently clear. Here, we expressed, identified and located the chitinase-like protein of S. scabiei (SsCLP), and evaluated its potential as an early-stage diagnostic antigen for rabbit scabies. Indirect ELISA using recombinant SsCLP (rSsCLP) exhibited diagnostic sensitivity of 94.4% (17/18) and specificity of 86.7% (26/30). Early diagnostic test after artificial infection of rabbits with S. scabiei for 1 week showed a positive detection rate of 96.7% (29/30). Immunolocalization assays showed that fluorescence signals were localized on the surface of mites and, in infected rabbits, were observed in keratinized skin and embedded mites. Intradermal skin tests of rabbits by injecting rSsCLP showed a wheal, flare and erythema reaction. These results suggest that S. scabiei chitinase-like protein is conducive to host invasion, participates in inducing the allergic response of the host, and is an effective antigen for the diagnosis of S. scabiei.

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.

Transcriptome-microRNA analysis of Sarcoptes scabiei and host immune response

Scabies is a parasitic disease, caused by the mite Sarcoptes scabiei, and is considered one of the top 50 epidemic diseases and one the most common human skin disease, worldwide. Allergic dermatitis, including an intense itch, is a common symptom, however diagnosis is difficult and there is currently no effective vaccine. The goal of this study was to examine the immune interaction mechanism of both S. scabiei and infected hosts. mRNA-seq and microRNA-seq were conducted on the S. scabiei mite and on infected and uninfected hosts. We focused on differential expression of unigenes and microRNAs, as well as the real targets of unigenes in enriched immune signaling pathways. S. scabiei enhanced host immune function and decreased metabolism after infection, while the immune response of the host inhibited S. scabiei proliferation and metabolism signaling pathways. Differentially expressed unigenes of S. scabiei were enriched in the JAK-STAT signaling pathway and the Toll-like receptor signaling pathway. The differential expression analysis indicated that microRNAs of S. scabiei and hosts have major roles in regulating immune interactions between parasites and hosts.

Vaccination of rabbits with immunodominant antigens from Sarcoptes scabiei induced high levels of humoral responses and pro-inflammatory cytokines but confers limited protection

BACKGROUND

Vaccination is an attractive ecological alternative to the use of acaricides for parasite control. However, effective anti-parasite vaccines against sarcoptic mange have not yet been developed. The purpose of this study was first to identify Sarcoptes scabiei immunodominant antigens and second to evaluate them as vaccine candidates in a rabbit/S. scabiei var. cuniculi model.

METHODS

The S. scabiei Ssλ15 immunodominant antigen was selected by immunoscreening of a S. scabiei var. hominis cDNA. The full-length cDNA was sequenced and cloned into the pGEX vector and the recombinant protein expressed in BL21 (DE3) cells and purified. A vaccination trial was performed consisting of a test group (n = 8) immunised with recAgs (a mix of two recombinant antigens, Ssλ15 and the previously described Ssλ20∆B3) and a control group (n = 8) immunised with PBS. All analyses were performed with R Statistical Environment with α set at 0.050.

RESULTS

The full-length open reading frame of the 1,821 nt cloned cDNA encodes a 64 kDa polypeptide, the sequence of which had 96 % identity with a hypothetical protein of S. scabiei. Ssλ15 was localised by immunostaining of skin sections in the tegument surrounding the mouthparts and the coxa in the legs of mites. Rabbit immunisation with recAgs induced high levels of specific IgG (P < 0.010) and increased levels of total IgEs. However, no significant clinical protection against S. scabiei challenge was detected. Unexpectedly, the group immunised with the recAgs mix had significantly higher lesion scores (P = 0.050) although lower mean mite densities than those observed in the control group. These results might indicate that the lesions in the recAgs group were due not only to the mites density but also to an exacerbated immunological response after challenge, which is in agreement with the specific high levels of pro-inflammatory cytokines (IL-1 and TNFα) detected after challenge in this group.

CONCLUSIONS

The selected antigens delivered as recombinant proteins had no clinical protective efficacy against S. scabiei infestation although immunisation reduced mite density. However, these results pave the way for future studies on alternative production systems, adjuvants, delivery methods and combinations of antigens in order to manage stimulation of clinical protective immune responses.

Prospective study in a porcine model of sarcoptes scabiei indicates the association of Th2 and Th17 pathways with the clinical severity of scabies

Background

Understanding of scabies immunopathology has been hampered by the inability to undertake longitudinal studies in humans. Pigs are a useful animal model for scabies, and show clinical and immunologic changes similar to those in humans. Crusted scabies can be readily established in pigs by treatment with the glucocorticoid dexamethasone (Dex).

Methodology/ Principal Findings

Prospective study of 24 pigs in four groups: a) Scabies+/Dex+, b) Scabies+/Dex-, c) Scabies-/Dex+ and d) Scabies-/Dex-. Clinical symptoms were monitored. Histological profiling and transcriptional analysis of skin biopsies was undertaken to compare changes in cell infiltrates and representative cytokines. A range of clinical responses to Sarcoptes scabiei were observed in Dex treated and non-immunosuppressed pigs. An association was confirmed between disease severity and transcription of the Th2 cytokines IL-4 and IL-13, and up-regulation of the Th17 cytokines IL-17 and IL-23 in pigs with crusted scabies. Immunohistochemistry revealed marked infiltration of lymphocytes and mast cells, and strong staining for IL-17.

Conclusions/ Significance

While an allergic Th2 type response to scabies has been previously described, these results suggest that IL-17 related pathways may also contribute to immunopathology of crusted scabies. This may lead to new strategies to protect vulnerable subjects from contracting recurrent crusted scabies.

Scabies is a neglected tropical skin disease caused by the tiny parasitic mite Sarcoptes scabiei. Scabies is common in developing countries, and scabies outbreaks also occur in institutional settings worldwide. Scabies often underlies secondary bacterial skin infection and resulting complications, and is thus associated with considerable morbidity. Crusted scabies is a an extremely severe and debilitating clinical form of the disease, but host immune responses leading to the development of crusted or ordinary scabies are poorly understood. This is largely due to limited access to clinical samples, and the difficulty in monitoring the progression of infestation in human patients. We have overcome this challenge by using a pig model of scabies infestation, since pigs and humans with scabies display clinical and immunological similarities. In this study, we undertook longitudinal analysis of clinical, histological and molecular immunological changes in pigs experimentally infected with scabies. We confirmed that disease severity was associated with a pronounced allergic, Th2 immune response, as previously reported. In a novel finding, we showed that the Th17 associated cytokines interleukin-17 and interleukin-23 were also associated with the development of crusted scabies. This may lead to new immunotherapeutic strategies to protect vulnerable subjects from contracting recurrent crusted scabies.

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.