In vitro demonstration of specific immunological hypersensitivity to scabies mite

Scabies by Kenneth Mellanby

Background:

Epidemics of scabies are often associated with wars or other times of social upheaval. This was particularly evident during the Second World War when it was estimated that there were one to two million patients with scabies in Great Britain.

Objective:

This article reviews the work of the zoologist Kenneth Mellanby of England and evaluates his contribution to our knowledge of the diagnosis and treatment of scabies in the Second World War.

Conclusion:

Using humans, Mellanby studied the transmission and treatment of this disease. Among his contributions were knowledge of how many mites the average patient had, and where they were located. He clearly noted and described that the scabies rash was not limited to the location of the mites on the body; he attributed the rash in areas with no mites to “a true sensitization.” He found that “fomites were not the major method of transmissions.”

Group 10 allergens (tropomyosins) from house-dust mites may cause covariation of sensitization to allergens from other invertebrates

Group 10 allergens (tropomyosins) have been assumed to be a major cause of cross-reactivity between house-dust mites (HDMs) and other invertebrates. Despite all of the published data regarding the epidemiology, percent IgE binding and level of sensitization in the population, the role of tropomyosin as a cross-reactive allergen in patients with multiple allergy syndrome still remains to be elucidated. Homology between amino acid sequences reported in allergen databases of selected invertebrate tropomyosins was determined with Der f 10 as the reference allergen. The 66.9 and 54.4% identities were found with selected crustacean and insect species, respectively, whereas only 20.4% identity was seen with mollusks. A similar analysis was performed using reported B-cell IgE-binding epitopes from Met e1 (shrimp allergen) and Bla g7 (cockroach allergen) with other invertebrate tropomyosins. The percent identity in linear sequences was higher than 35% in mites, crustaceans, and cockroaches. The polar and hydrophobic regions in these groups were highly conserved. These findings suggest that tropomyosin may be a major cause of covariation of sensitization between HDMs, crustaceans, and some species of insects and mollusks.

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.

Generalized granuloma annulare associated with scabies

Granuloma annulare (GA) is a common dermatosis of unknown etiology, which, in 10%-15% of cases, presents as the generalized subtype. GA has been associated with infections, vaccines, and neoplasias. We describe a case of generalized GA arising in a 50-year-old man with a diffuse infestation by Sarcoptes scabiei.

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.

Treatment of Neotrombicula autumnalis dermatitis in dogs using two topical permethrin-pyriproxyfen combinations

Few data are available in the literature on the dermatological consequences and treatment of Neotrombicula autumnalis infestation in dogs and cats. In this study, 15 dogs naturally infested with Neotrombicula were affected with moderate to severe pruritic dermatitis. The dermatitis resolved with successful treatment of the parasitic infestation. In 14 dogs, treatment using a topical permethrin-pyriproxyfen combination (pump-spray or 'line-on') was effective within one to three weeks. Two applications were necessary in four dogs. Careful follow-up was conducted in all cases. Statistical analysis was performed to assess the impact of treatment on the parasite population and clinical signs over the three-week study period.

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

Parasitic infestation of the skin by the mite Sarcoptes scabiei is a significant problem worldwide, particularly in socially disadvantaged communities. A multigene family of at least 24 homologs of a serine protease allergen have been identified in S. scabiei. Surprisingly, the products of all but one of these genes are predicted to be catalytically inactive, due to mutations at a critical triad of amino acids at the active site. We discuss the possibility that these genes for inactivated proteases have been conserved because they mediate a novel host defense evasion strategy that the mite has evolved as an adaptation to parasitism of the epidermis. The identification of this family, and elucidation of its value to the parasite, may present an unanticipated approach to protective vaccination.

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.

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.

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.

An overview of sexually transmitted diseases. Part II

Sexually transmitted diseases are a persistent problem in the United States and throughout the world. Many of these infections involve the skin and may be encountered in the field of dermatology. This 3-part review highlights the cutaneous features, diagnosis, and treatment of 11 of the most common sexually transmitted diseases, other than AIDS. The second part of this series focuses on anogenital warts, chronic viral hepatitis, molluscum contagiosum, scabies, and pediculosis pubis. Additional features, such as epidemiology and transmission of the organism, are discussed when applicable. (J Am Acad Dermatol 1999;41:661-77.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be familiar with the clinical features, diagnosis, and treatment of sexually transmitted diseases (excluding AIDS) which have cutaneous presentations or involvement.

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.

The role of mast cells in treatment of scabies

OBJECTIVE

The purpose of this study was to recognize the role of mast cells in the pathogenesis of scabies.

METHODS

One hundred and fifty patients and 10 controls were included in the study. Group 1 included 20 patients without previous treatment. In group 2, 80 patients were treated with antiscabietic drugs. Group 3 had 50 patients who received an antiscabietic drug followed by 3 days of crotamiton. Diurnal and nocturnal skin biopsies were taken from group 1. In groups 2 and 3, the biopsies were taken after 2 weeks of treatment. Sections were cut and stained by hematoxylin and eosin and Giemsa stains.

RESULTS

Mast cells were increased in diurnal and nocturnal biopsies. Evident degranulation of mast cells was detected in nocturnal biopsies. The mast cell number decreased to half its pretreatment number in patients treated with antiscabietic drugs and to its normal number in patients treated with antiscabietic drugs followed by 3 days with crotamiton.

CONCLUSION

The number of mast cells are increased in scabietic lesions. This plays a role in the pathogenesis of the clinical and histologic picture of scabies. We recommend that an antiscabietic drug should be followed by 3 days of crotamiton in the treatment of scabies.

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.

Density of itch mite, Sarcoptes scabiei (Acari: Sarcoptidae) and temporal development of cutaneous hypersensitivity in swine mange

Experimental infestations of Sarcoptes scabiei (De Geer) were established to study development of cutaneous hypersensitivity in pigs. Forty-eight pigs in six isolation rooms were used in two trials lasting 51 and 65 days, respectively. Treatments of 0 (control), 100 (low dose), and 1000 mites (high dose) per pig were randomly assigned to rooms. Intradermal skin tests with a sterile mite extract were done weekly to assess hypersensitivity. Control pigs never responded to the extract, whereas most infested pigs progressed through phases of (1) no response, (2) delayed hypersensitivity alone, (3) immediate and delayed hypersensitivity together, and (4) immediate hypersensitivity alone. High-dose pigs developed delayed and immediate hypersensitivity sooner than low-dose pigs (P less than 0.005). When related to cumulative mite-days, a measure of exposure to mite antigens, low-dose and high-dose pigs developed delayed responses after experiencing the same level of exposure. Thereafter, immediate responses developed sooner in low-dose pigs, suggesting that immediate hypersensitivity develops at a rate that is independent of rate of antigen exposure.

The effect of sarcoptic mange on growth performance, leukocytes and lymphocyte proliferative responses in pigs

The effects of a single artificial infestation with sarcoptic mite (Sarcoptes scabiei var. suis DeGeer) on weight gain and lymphocyte blastogenic responses were studied in untreated and fenvalerate-treated pigs. Average daily feed intake, average daily gain and feed efficiency were monitored for 5 weeks in 32 infested and 16 uninfested pigs. Total and differential leukocyte counts were determined and lymphocyte proliferative responses, using a mitogen-stimulated lymphocyte blastogenesis assay, were evaluated in 24 pigs. Sarcoptic mite infestation or treatment for sarcoptic mange did not affect total or differential leukocyte counts (P greater than 0.10). Differences were not observed in weight gain or lymphocyte blastogenic responses between infested and uninfested pigs.

Scabies and lice

Scabies and pediculosis, two commonly encountered infestations both having an incidence that is on the rise, are discussed in detail in this article with special emphasis given to their symptomatology, pathogenesis, and treatment.

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.

Cross infestivity of Sarcoptes scabiei

Sarcoptes scabiei var. canis was successfully transferred from the dog to New Zealand White Rabbits, Oryctologus cuniculus. Natural and experimental transfers were accomplished between rabbits. The dog strain transferred to rabbits showed no morphologic changes and was readily transferred back to dogs. Experimental transfer of var. canis to guinea pigs and pigs resulted in only temporary infestation. Attempts to infest haired and hairless mice, thymus-deficient (nude) mice, and rats were unsuccessful. The unsuccessful or transient nature of cross-infestations between some host species and complete cross-infestation in others leads to the conclusion that all S. scabiei varieties are not host-specific but that they do possess some degree of host preference and that physiologic differences between varieties exist.

Scabies and systemic lupus erythematosus

There is little information in the literature concerning scabies in patients with systemic lupus erythematosus. Scabies in our five patients appeared to be more severe than usual, and two of them developed crusted scabies, probably on an immunologic basis.

Antibodies to Dermatophagoides pteronyssinus allergen Dpt 12 contaminating rabbit antisera to human and mouse anti-immunoglobulins

Antibodies to the allergen Dpt 12 from Dermatophagoides pteronyssinus have been demonstrated in commercially obtained rabbit anti-human IgE, IgG and IgA antisera and in a commercially obtained rabbit anti-mouse IgG1 antiserum using either double or triple antibody radioimmunoassays. Where measurable, the titre of anti-Dpt 12 antibodies varied both between different anti-isotypes and between batches of the same anti-isotype as judged by the dilution of antiserum required to bind 50% of the radiolabelled Dpt 12. The titres ranged from 1/23-1/360. In contrast, a specific rabbit anti-Dpt antiserum gave a titre of 1/4500.

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.