IgE antibodies to house dust mite in patients with scabies

Scabies: a review of diagnosis and management based on mite biology

Scabies is a contagious parasitic dermatitis that is a significant cause of morbidity, especially outside of the United States. Scabies is diagnosed most often by correlating clinical suspicion with the identification of a burrow. Although scabies should be on the differential for any patient who presents with a pruritic dermatosis, clinicians must consider a wide range of diagnostic possibilities. This approach will help make scabies simultaneously less over- and underdiagnosed by clinicians in the community. Atypical or otherwise complex presentations may necessitate the use of more definitive diagnostic modalities, such as microscopic examination of KOH prepared skin scrapings, high-resolution digital photography, dermoscopy, or biopsy. Scabies therapy involves making the correct diagnosis, recognizing the correct clinical context to guide treatment of contacts and fomites, choosing the most effective medication, understanding how to use the agent properly, and following a rational basis for when to use and reuse that agent. Although the development of new therapeutic agents is always welcome, tried and true treatments are still effective today. Permethrin is the gold standard therapy, with malathion being an excellent topical alternative. Ivermectin is an effective oral alternative that is especially useful in crusted scabies, patients who are bed ridden, and in institutional outbreaks. Despite the availability of effective therapeutics, treatment failures still occur, mostly secondary to application error (ie, failure to treat the face and scalp or close contacts, failure to reapply medication) or failure to decontaminate fomites. Because increasing resistance to scabies treatments may be on the horizon, we propose that standard of care for scabies treatment should involve routine treatment of the scalp and face and re-treating patients at day 4 on the basis of the scabies life cycle to ensure more efficient mite eradication. Practitioners should attempt to treat all close contacts simultaneously with the source patient. To eradicate mites, all fomites should be placed in a dryer for 10 minutes on a high setting, furniture and carpets vacuumed, and nonlaunderables isolated for a minimum of 2 days, or, for those who wish to be rigorous, 3 weeks.

Recent developments in the diagnosis of ectoparasite infections and disease through a better understanding of parasite biology and host responses

Some conventional methods of diagnosis of ectoparasite infections can have low sensitivity and/or specificity. In addition, early infestations, sub-clinical and carrier hosts often go un-diagnosed, allowing infestations to spread. This review focuses on the important ectoparasites of human, livestock and companion animals for which improved diagnostic tools are either already in use, or in development. These advances in diagnostic technologies have resulted in improved treatment, control and preventative strategies for many ectoparasitic diseases. Immunodiagnostic methods have had a large impact, with the emergence of highly sensitive and specific enzyme-linked immunosorbent assays (ELISAs) for sarcoptic and psoroptic mange, with further improved tests in development. In the present review, the advantages and limitations of such tests are discussed and the potential for future development explored. The increasing use of molecular tools, for example, PCR and other molecular methods, has improved our understanding of the epidemiology of ectoparasitic diseases, with practical consequences for community-based control programmes. Recently, the identification of specific signalling pathways during the host response to ectoparasites has led to the identification of disease biomarkers which, along with new technologies, such as multiplexed assays and microfluidic platforms, could lead to more cost-effective, rapid and accurate diagnosis of infectious diseases.

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.

Problems in diagnosing scabies, a global disease in human and animal populations

Scabies is a worldwide disease and a major public health problem in many developing countries, related primarily to poverty and overcrowding. In remote Aboriginal communities in northern Australia, prevalences of up to 50% among children have been described, despite the availability of effective chemotherapy. Sarcoptic mange is also an important veterinary disease engendering significant morbidity and mortality in wild, domestic, and farmed animals. Scabies is caused by the ectoparasitic mite Sarcoptes scabiei burrowing into the host epidermis. Clinical symptoms include intensely itchy lesions that often are a precursor to secondary bacterial pyoderma, septicemia, and, in humans, poststreptococcal glomerulonephritis. Although diagnosed scabies cases can be successfully treated, the rash of the primary infestation takes 4 to 6 weeks to develop, and thus, transmission to others often occurs prior to therapy. In humans, the symptoms of scabies infestations can mimic other dermatological skin diseases, and traditional tests to diagnose scabies are less than 50% accurate. To aid early identification of disease and thus treatment, a simple, cheap, sensitive, and specific test for routine diagnosis of active scabies is essential. Recent developments leading to the expression and purification of S. scabiei recombinant antigens have identified a number of molecules with diagnostic potential, and current studies include the investigation and assessment of the accuracy of these recombinant proteins in identifying antibodies in individuals with active scabies and in differentiating those with past exposure. Early identification of disease will enable selective treatment of those affected, reduce transmission and the requirement for mass treatment, limit the potential for escalating mite resistance, and provide another means of controlling scabies in populations in areas of endemicity.

Scabies: a ubiquitous neglected skin disease

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

Mite allergens

There is an increasing awareness of the health implications of mite sensitivity, as it is closely related to asthma. Mite allergy constitutes a complex worldwide problem, with sanitary and economical implications. Not only are mite species present in house dust, producing potent allergens, but other, less studied species are also responsible for significant allergic reactions in occupational settings. In this review, we focus on the growing number of mite species that are implicated in allergic cutaneous and respiratory diseases in humans. Mite allergy is not restricted only to the human "indoor" environment, because numerous reports clearly demonstrate that many species that can induce sensitization and symptoms are encountered in occupational settings. An important component of allergy research is the evaluation of the allergenic cross-reactivity to verify to what extent different mite species have unique, species-specific, or cross-reactive allergens. The results of these investigations have important clinical consequences for the diagnosis and treatment of allergic diseases. Internationally standardized mite extracts are needed to compare sensitization rates around the world and clearly establish risk factors associated with sensitization and asthma. In spite of recent controversial results, a significant reduction in the exposure to mite allergens continues to be an important challenge and one of the main goals in the treatment of mite-induced respiratory symptoms. In many cases, this reduction must be achieved in the workplace as well as in the home environment.

Atopy Patch Test Reactions to House Dust Mites in Patients with Scabies

It is well known that the house dust and the scabies mites are related phylogenetically. We therefore performed atopy patch tests with house dust mite antigens (Dermatophagoides pteronyssinus (Dp) and/or Dermatophagoides farinae (Df)) in scabies patients without atopy and healthy controls. We studied 25 men with active scabies and 25 healthy controls. Skin prick tests with standardized house dust mite extract were performed for all patients and controls. An intradermal test procedure was carried out in skin prick test-negative patients, and for controls showing positive atopy patch test to Dp and/or Df. While atopy patch tests were performed directly in all healthy controls, patients with scabies were first treated and on the next day, atopy patch tests were performed. Twenty-two of 25 patients with scabies (88%) had skin prick test and/or intradermal test positivity against house dust mites, whereas 17/25 patients (68%) had atopy patch test positivity against house dust mites (Dp and/or Df). There was no statistically significant difference between skin prick test and/or intradermal test positivity and atopy patch test positivity in a regression analysis (p=0.222). The only statistically significant correlation was between atopy patch test positivity and the extent of scabies involvement (p<0.05). Only few of the healthy controls had positive tests. In this study, we have shown that a positive atopy patch test to house dust mite antigens is not specific for patients with atopic dermatitis, but also occurs in scabies patients without a history of atopic dermatitis.

Scabies: New Future for a Neglected Disease

Scabies is a disease of global proportions in both human and animal populations, resulting from infestation of the skin with the "itch" mite Sarcoptes scabiei. Despite the availability of effective chemotherapy the intensely itching lesions engender significant morbidity primarily due to secondary sepsis and post-infective complications. Some patients experience an extreme form of the disease, crusted scabies, in which many hundreds of mites may infest the skin causin severe crusting and hyperkeratosis. Overcrowded living conditions and poverty have been identified as significant confounding factors in transmission of the mite in humans. Control is hindered by difficulties with diagnosis, the cost of treatment, evidence for emerging resistance and lack of effective vaccines. Historically research on scabies has been extremely limited because of the difficulty in obtaining sufficient quantities of the organism. Recent molecular approaches have enabled considerable advances in the study of population genetics and transmission dynamics of S. scabiei. However, the most exciting and promising development is the potential exploitation of newly available data from S. scabiei cDNA libraries and EST projects. Ultimately this knowledge may aid early identification of disease, novel forms of chemotherapy, vaccine development and new treatment possibilities for this important but neglected parasite.

Arthropod allergens and human health

Many species of arthropods are the sources of potent allergens that sensitize and induce IgE-mediated allergic reactions in humans. Most of these arthropod allergens are proteins, and the allergic response mechanism to these allergens is the same as it is for allergens from other sources such as plant pollens, molds, and foods. Aside from ingestion of crustaceans (shrimp, lobster), among arthropods, humans have the greatest contact with insects and mites, and as a result allergies to these two groups of arthropods have been the most frequently reported. Because of the large number of people affected by allergic reactions to stinging insects, cockroaches, and dust mites, many allergens of these organisms have been extensively studied, purified, and immunobiochemically characterized and for some recombinant allergens, produced. Cocktails of these recombinant allergens have the potential for use in diagnosis and immunotherapy. In this chapter, we review the insects and mites that induce allergic reactions. Where the information exists, the immunobiochemical characterization of the allergens and the frequency of sensitivity or clinical reactivity in the human population are also reviewed. As background, the beginning of this review includes sections that define allergens, explain the allergic reaction mechanism, and describe the methods for naming allergens.

Evaluation of an enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of sarcoptic mange in dogs

Canine scabies is a challenging disease to diagnose because sarcoptic mites are hard to find on skin scrapings. The purpose of this study was to evaluate a serologic enzyme-linked immunosorbent assay (ELISA) as an aid in the diagnosis of canine scabies. In addition, serum samples were obtained post treatment to determine the duration and persistence of circulating scabies antibodies after resolution of natural infection. Nineteen dogs diagnosed with sarcoptic mange and 38 control dogs were tested. Sixteen scabies-infested dogs showed positive pretreatment ELISA results (84.2% sensitivity). Thirty-four control dogs showed negative ELISA results (89.5% specificity). In the 11 scabies dogs from which multiple post treatment serum samples were obtained, detectable antibodies were not present 1 month after treatment in four cases, but were present for 1-4.5 months post treatment in seven dogs. Our results suggest that this scabies ELISA test is useful in the diagnosis of canine scabies.

Dust mites: update on their allergens and control

Mites are ubiquitous organisms, and as a result, humans come into contact with mites and mite products in a variety of situations. Molecules from many mite species can induce IgE-mediated reactions. Best known among the allergy-causing mites are the house dust and storage mites. However, allergists should be aware that, in specific situations, contact with products of many other less-known species of mites also may cause IgE-mediated reactions.

Serum antibody to Sarcoptes scabiei and house dust mite prior to and during infestation with S. scabiei

In this study, serum antibodies to Sarcoptes scabiei var. canis (SS), Dermatophagoides farinae (DF), and D. pteronyssinus (DP) were determined in 19 healthy, random-source dogs prior to infestation with scabies then again during a primary infestation, cure and challenge infestation with scabies. Prior to scabies infestation, serum of 11 dogs contained faintly detectable amounts of IgE and/or IgG to proteins in SS extract, probably resulting from sensitization to dust mites that share cross-reactive antigenic epitopes with SS. After becoming infested with scabies, the response to SS antigens became stronger with antibodies appearing to more antigens as the scabies infestation progressed. Three of the newly recognized proteins were 170, 155 and 142/133kD and could be used in a diagnostic test since antibodies to them appeared during the primary infestation. In addition, during the primary infestation, 14 of 15 dogs developed IgE to 1-11 new SS proteins in addition to an increase in IgE binding to those proteins recognized prior to infestation. Overall, the strongest antibody responses (IgE and IgG) were exhibited during cure of the first infestation, when dead mites were still present in the stratum corneum. As expected, the antibody response was strong and rapid during challenge when the infestation self-cured. The immunogenic SS proteins identified by serum antibody binding during challenge, when the hosts self-cured, are candidates for inclusion in a vaccine. These candidate proteins are 200, 185, 170, 155, 142/133, 112, 97, 74, 57, 45/42, 32 and 22kD. Some of the proteins in SS that exhibited new or increased antibody binding during the experiment also had IgE and IgG binding to proteins with similar molecular weights in DF and DP extracts. These results illustrate the difficulties involved in understanding and interpreting serum antibody for developing a serological test for the diagnosis of scabies, isolating relevant SS antigens that could be included in a vaccine for prevention of scabies, and for understanding the immune response mechanism to scabies.

The development of protective immunity in canine scabies

Seven of eight dogs that had been previously infested with Sarcoptes scabiei var. canis and then cured, expressed protective immunity when experimentally reinfested with scabies. All seven dogs that expressed resistance were spontaneously cleared of scabies by 64 days after they were experimentally reinfested. Five of the eight dogs were free of scabies by 24 days. The sequential changes in the inflammatory/immune cellular infiltrate in the scabietic lesions of each dog were determined during the sensitizing infestation, cure and the subsequent experimental reinfestation (challenge). During the initial infestation and in the subsequent challenge reinfestation, dogs developed mixed cellular infiltrates in their scabietic lesions that contained mononuclear cells, neutrophils, plasma cells and mast cells. Reinfestation induced more rapid increases in the densities of these cells than had occurred during the sensitizing infestation. Mononuclear and mast cells were the most numerous infiltrating cells during the sensitizing phase. During the challenge phase the most numerous infiltrating cells were mononuclear cells and neutrophils. The sensitizing and challenge infestations induced circulating scabies-specific antibody responses, but the response was more rapid during the reinfestation challenge. Both the cell-mediated response in the skin and the circulating antibody response waned in parallel with clearing of the mites following reinfestation.

House-dust mite content in mattresses in relation to residential characteristics and symptoms in atopic and nonatopic children living in northern Norway

The occurrence of house-dust mites (HDMs) was investigated in the mattresses of 19 children previously found to be skin prick test (SPT) positive to HDM and in 19 nonatopic children derived from an extensive survey of 424 schoolchildren, all living in northern Norway. Domestic mites were counted and identified microscopically. Mite counts ranging from 10 to 1800 mites per gram mattress dust were found in 10 of the 19 HDM-sensitized children compared to none in the control group, corresponding to an odds ratio of more than 20. Of the 540 domestic mites found, 70 were identified by species. Dermatophagoides pteronyssinus (Dpt) was the only HDM species identified (64 mites), while five were storage mites and one was a Tarsonemus species. Positive radioallergosorbent tests (RAST) to Dpt were demonstrated in 9/10 children with and in 5/9 without mite infestation compared to none in the control group. Elevated IgE levels were also found more frequently in children with mite-infested mattresses than in those without. IgE levels were within normal levels in all 19 children in the control group. Latent atopy was found in four children, three with and one without mite infestation. There was no correlation between the concentration of mites and the degree of sensitization. Poor ventilation, increased humidity, and water leak(s) were associated with the presence of domestic mites in mattresses. As HDM growth is highly dependent on humidity and microhabitat, it should be possible to avoid HDM exposure and allergy in this region.

Scabietic nodules: a dermatopathologic and immunofluorescent study

Mites and their eggs were thought to be rarely found in nodular lesions of scabies. However, serial sections from 27 scabietic scrotal papules or nodules revealed mite parts in 22% (6/27). This supports the contention that scabietic nodules may result from persisting antigens of mite parts. In contrast to previous studies, vasculitis with fibrinoid degeneration was uncommon (3/27) in our series. This discrepancy may be due to the timing of the biopsies: 2 of 3 cases with vasculitis were associated with diffuse dense infiltration, and vasculitis may be a late event in the development of scabietic nodules. The specificity of immunoreactant deposits along the epidermodermal junction (EDJ) in scabies is controversial. In our study, direct immunofluorescence (DIF) was performed on 13 scabietic nodules. Four (31%) showed immunoreactants at the EDJ and two on blood vessels. Because of the relatively low positive rate, the low intensity of fluorescence, and 3 of 4 cases with positive immunoreactants having only a single class of immunoglobulin, the deposition may only be secondary to inflammation instead of a specific type II immunologic reaction to scabies.

Responses of immunoglobulin-secreting cells in the skin of pigs during Sarcoptes scabiei infestation

Investigations using immunofluorescence and immunoperoxidase techniques revealed a gradual, but marked, increase in the numbers of immunoglobulin-secreting cells in the skin of pigs during the development of lesions of sarcoptic mange. This was followed by a marked decrease as the lesions regressed. The rise and fall in numbers of these immunoglobulin-secreting cells were observed in both newborn and older animals as they developed signs of cutaneous disease. IgG-secreting cells were the major immunoglobulin-containing cells, followed by IgM- and then IgA-containing cells in the skin of newborn animals. In older pigs, IgM-secreting cells were most prevalent, followed by IgG- and IgA-secreting cells. In multiple infestations, immunoglobulin-secreting cells in the dermis showed very little increase in numbers following the second infestation. Third, fourth and fifth infestations produced little or no increase.

Serum IgE antibodies to the scabies mite

Porcine scabies mites, Sarcoptes scabiei var. suis are more readily available in sufficient quantities than are human scabies mites. Circulating IgE antibodies specific to porcine scabies mites were found in 6 (30%) of 20 scabies patients with an RAST score of at least 2. Seven patients had elevated serum total IgE levels. Correlation between the RAST values, the duration of pruritus, and the IgE levels was not found. The results do not prove the existence of antibodies specific to porcine scabies mites but strongly support this assumption.

Immunomodulation of host responses to ectoparasite infestation--an overview

Immune reactivity stimulated by ectoparasites and other arthropods has received increased attention in recent years. It is clear that a broad range of host responses are elicited, and immune effector mechanisms appear to be active in limiting infestation with blood-feeding arthropods. Host immune responsiveness appears to be altered as a consequence of infestation by certain arthropods, and the impact of these alterations on vector-borne pathogen transmission remains to be determined. Successful techniques have been developed by a number of investigators for the artificial induction of resistance to blood-feeding arthropods. These areas are examined in this paper.

Host-parasite relationships in hyperkeratotic (Norwegian) scabies: pathological and immunological findings

The dynamics of intraepidermal penetration of the scabies mite and the host's responses to the invaders have been studied in hyperkeratotic scabies. Contrary to the generally accepted view, the mites progressed not only through the stratum corneum but also into the underlying epidermis and even occasionally to the dermo-epidermal interface. Morphological evidence of reactive processes included parakeratosis surrounding the burrows, psoriasiform hyperplasia with increased basal cell labelling indices and exocytosis of mononuclear cells. 3H-Thymidine labelling indices of immunocompetent cells of the dermal infiltrate reached levels found in allergic patch test reactions and were in both cases higher than in non-immune-specific inflammatory processes. The labelling index of peripheral blood lymphocytes showed an increased ratio of B cells to T cells as compared to controls or patients with allergic contact dermatitis. Serum CIq fixation was higher than in untreated patients with common scabies. These results support our previous findings of immunological activation in host infested by the scabies mite.

Immunologic studies in scabies

Various materials related to the life physiology of the scabies mite in and on the human skin have been identified by morphology. The role they could play as possible activators of both cellular and humoral arms of the host's immune system is discussed. Subtle aberrations of this reactive process could be basically responsible for the wide spectrum of clinical and histological aspects reported in scabies. Possible lines for future research on host-parasite relationship in scabies are proposed.

Antigens Common to Scabies and House dust Mites

Twenty-five antigens were demonstrated in a crude Dermatophagoides farinae (DF) extract by means of crossed immunoelectrophoresis (CIE), using a rabbit anti-DF serum. With the same antiserum, four antigens were demonstrated in a scabies mite preparations, indicating an immunological relationship between these scabies antigens and some of the DF antigens. In tandem CIE experiments the DF antigens were found to be partly identical to three of the scabies antigens. No IgE activity against any of these scabies antigens was evident in pooled sera from patients with house dust mite allergy by crossed radioimmunoelectrophoresis. However, one such patient had IgE antibodies to a DF antigen and a partial identical scabies antigen.

Serum IgE before and after treatment for scabies

In 120 patients, treated for scabies infection, the serum IgE concentrations fell from high levels in 54 and normal levels in 66 to lower levels 12 months after treatment. The specific IgE antibodies to Dermatophagoides pteronyssinus (RAST) were also reduced 12 months after treatment. The decrease in both IgE concentrations and IgE antibodies was most conspicuous in non-atopic patients. These findings confirm previous observations of specific immunological hypersensitivity to scabies mite, and that scabies infection stimulates the production of IgE antibodies.

HLA antigens in patients with scabies

Sixty patients with scabies were typed for thirty-three antigens of the HLA-A, -B and -C series. A significantly increased frequency was found for HLA-AII (28.3%), compared to healthy controls (10.4%). This deviation was only found in those of the patients without signs of atopic disease.

In vitro demonstration of specific immunological hypersensitivity to scabies mite

An extract prepared from 200 adult female scabies mites was used for prick and intracutaneous testing in twelve patients with previous scabies infestation, as well as in six healthy controls and three persons with skin sensitivity to Dermatophagoides pteronyssinus who had never had scabies before. Seven individuals who had had scabies less than a year prior to the testing had positive intracutaneous (immediate type) reactions, whereas all the five who had had scabies more than a year before had negative reactions. The prick tests were negative in all cases. No skin reactions could be evoked in the controls. The passive transfer, or Prausnitz-Küstner, test was positive with the scabies mite extract and serum from three of five patients tested on one healthy individual, and with both of two sera tested on a second healthy individual. These findings indicate that immediate type hypersensitivity reactions may occur with scabies infection.