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

Comparative analysis of the allergenic characteristics and serodiagnostic potential of recombinant chitinase-like protein-5 and -12 from Sarcoptes scabiei

Background

Scabies is caused by burrowing of the mite Sarcoptes scabiei into the stratum corneum. Currently, diagnosis via routine skin scraping is very difficult, and information on the allergenic identification of S. scabiei remains limited.

Methods

We performed comparative analysis of the serological diagnostic potential of recombinant S. scabiei chitinase-like protein-5 (rSsCLP5) and recombinant S. scabiei chitinase-like protein-12 (rSsCLP12) by measuring the levels of serum-specific IgG and IgE antibodies (Abs) as diagnostic markers. In addition, the allergenic characteristics of rSsCLP5 and rSsCLP12 were evaluated using IgE-binding experiments and skin tests.

Results

The IgE Abs-based indirect enzyme-linked immunosorbent assay (ELISA) methods showed high sensitivity and specificity: the rSsCLP5-based assay had 93.5% sensitivity and 94.4% specificity; the rSsCLP12-based assay had 100% sensitivity and 98.1% specificity. The specific IgE Abs in infested mouse sera could bind rSsCLP5 and rSsCLP12. In skin tests, rabbits in the rSsCLP5 and rSsCLP12 groups and positive control (histamine) groups exhibited allergic reactions. Most test sites in the rSsCLP12 group had edema, bleeding spots, and even ulcers or scabs, but such allergy symptoms were rare in the rSsCLP5 group. Moreover, the allergic history rabbit group had more severe allergic reactions and lower levels of IgE Abs compared to the healthy rabbit group in the same protein group.

Conclusions

These findings validate the use of IgE Abs to rSsCLP5 and rSsCLP12 as potentially useful markers for diagnosing scabies. Moreover, both rSsCLP5 and rSsCLP12 have allergenic properties, and the potential allergen rSsCLP12 is a stronger allergen than rSsCLP5.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04654-0.

First description of sarcoptic mange in the endangered Iberian lynx (Lynx pardinus): clinical and epidemiological features

A 6-month-old female Iberian lynx (Lynx pardinus) cub that was severely affected by mange died in September 2016 in the Montes de Toledo (Spain) with crusts and fissures on its face, outer ears, nipples and footpads. The body condition of the cub was very poor, and it also had a mandibular abscess and a severely ankylosed luxation on its left knee. After confirming that the origin of the deceased cub’s dermal lesions was Sarcoptes scabiei, the subsequent search for ectoparasites and a comparison of histopathological and immunohistochemical findings in all sympatric lynxes handled (n = 30) and submitted for necropsy (n = 4) during 2016 and 2017 revealed the presence of S. scabiei mites and/or milder mange compatible lesions in five members of her family group, which was treated against mange together with two exposed contiguous family groups. An ELISA developed by the authors showed the presence of antibodies against S. scabiei in the deceased female cub and one brother. The presence of concomitant immunosuppressive factors in the dead female cub and the results obtained for the other sympatric lynxes studied since 2016 suggest that S. scabiei had a limited effect on immune-competent Iberian lynxes in the local population of the Montes de Toledo. However, a different evolution and relevance of sarcoptic mange in different populations—or even in the same one in the presence of immunosuppressive factors—cannot be ruled out, thus confirming the need for further research in order to attain a complete comprehension of the epidemiology and the real threat that this ectoparasitic disease may imply for L. pardinus.

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.

Evaluation of three enzyme-linked immunosorbent assays for sarcoptic mange diagnosis and assessment in the Iberian ibex, Capra pyrenaica

BACKGROUND

Sarcoptic mange is a contagious skin disease caused by the mite Sarcoptes scabiei, affecting different mammalian species worldwide including the Iberian ibex (Capra pyrenaica), in which mortalities over 90 % of the population have been reported. No efficient diagnostic methods are available for this disease, particularly when there are low mite numbers and mild or no clinical signs. In this study, three enzyme-linked immunosorbent assays (ELISA) developed for dog (ELISA A), Cantabrian chamois (Rupicapra pyrenaica parva) (ELISA B) and Alpine chamois (Rupicapra rupicapra) (ELISA C), were evaluated to detect specific antibodies (IgG) to sarcoptic mange in Iberian ibex sera.

METHODS

Serum samples from 131 Iberian ibexes (86 healthy and 45 scabietic) were collected from 2005 to 2012 in the Sierra Nevada Natural and National Parks (southern Spain). Based on visual inspection, ibexes were classified into one of three categories, namely healthy (without scabietic compatible lesions), mildly affected (skin lesions over less than 50 % of the body surface) and severely affected (skin lesions over more than 50 % of the body surface). The optimal cut-off point, specificity, sensitivity and the area under the curve (AUC) were calculated, and the agreement between tests was determined. Moreover, differences in the optical density (OD) related to scabies severity have been evaluated for the best test.

RESULTS

ELISA C showed better performance than the two other tests, reaching higher values of sensitivity (93.0 %) and specificity (93.5 %) against the visual estimation of the percentage of affected skin, chosen as the gold standard. Significantly higher concentrations of specific antibodies were observed with this test in the mildly and severely infested ibexes than in healthy ones.

CONCLUSIONS

Our results revealed that ELISA C was an optimal test to diagnose sarcoptic mange in the Iberian ibex. Further studies characterizing immune response during the course of the disease, including spontaneous or drug induced recovery, should follow in order to better understand sarcoptic mange in Iberian ibex populations.

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.

Evaluation of an ELISA using recombinant Ssλ20ΔB3 antigen for the serological diagnosis of Sarcoptes scabiei infestation in domestic and wild rabbits

An ELISA, based on the Sarcoptes scabiei Ssλ20ΔB3 inmunodominant antigen, was evaluated for the detection of antibodies to S. scabiei in experimentally infested (n=10), farm (n=109), and wild (n=78) rabbit sera. The S. scabiei antigen Ssλ20ΔB3, a major structural protein present over the entire mite's body, was produced as a recombinant protein in Escherichia coli and purified for its use in the ELISA. The resulting ELISA showed, in experimentally infested domestic rabbits, detectable specific antibody responses (IgG) above the cut off level from week three post-infestation indicating that the assay is able to detect positive rabbits very early during the course of the infestation. The ELISA was validated on a panel of 109 domestic breeding rabbit sera collected from 26 Spanish farms, of which 41 were obtained from rabbits with skin lesions compatible with sarcoptic mange, 26 with skin lesions compatible with psoroptic mange, and 42 from unexposed individuals from mange-free farms. The ELISA in this group was characterized by 95% sensitivity, 97% specificity, and a high degree of repeatability. In the psoroptic mange compatible lesions group, included in the study as control group for cross-reactivity with the closely related mite Psoroptes cuniculi, cross-reacting antibodies to Ssλ20ΔB3 S. scabiei antigen were detected in 42.30% of the rabbit sera. However, mean% OD values of the sarcoptic-mange group (55.61 ± 39.20%) were significantly higher (p<0.001) than OD values of the psoroptic-mange (3.64% ± 5.4%) and also of the free-mange (0.21% ± 0.67%) groups. In addition, the ELISA was also evaluated in serum samples obtained from both naturally infested and non-infested wild rabbits from Mallorca Island. The sensitivity of the assay for this group was 100% (4 out of the 4 rabbits with sarcoptic mange compatible lesions and presence of S. scabiei mites were seropositive) and the specificity was 90% (67 out of 74 wild rabbits without detectable mange lesions were seronegative). Although, the total number of tested samples from experimentally infested, farm and wild rabbits was limited, our study showed that the ELISA is able to differentiate between infested and non-infested animals in all tested groups with very high sensitivity and specificity indicating that recombinant Ssλ20ΔB3 is a reliable diagnostic antigen. This assay might be a cost-effective tool for detecting the presence of mangy animals and therefore helping prevent spread of mange among domestic rabbits, reducing potential transmission from female breeding rabbits to other farms, and detecting infestation with sarcoptic mange in the wild.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Autoantibodies to iron-binding proteins in pigs infested with Sarcoptes scabiei

Despite the availability of effective treatments, Sarcoptes scabiei remains a major health problem in the pig industry. Unsuccessful control of the disease is often due to the lack of reliable detection methods, with current tests relying on skin scrapings and crude antigen ELISAs. A previous analysis of antigens in pig skin scrapings reported that anti-transferrin antibodies were present in S. scabiei infected animals and that this finding might be considered as a useful diagnostic tool. This paper confirms IgG autoantibodies against transferrin, including the first report of IgM autoantibodies, in both naturally and experimentally infected pigs using ELISA and dot blot assays. Autoantibodies were also detected in pigs to ferritin and to a lesser extent lactoferrin. Immunoblotting confirmed the presence of IgG and IgM autoantibodies in mange positive pigs, as well as IgM antibodies to transferrin and albumin in mange negative pigs. These findings suggest the presence of natural autoantibodies to transferrin and albumin in pigs. The development of the IgG autoimmune response may either be a host mechanism for limiting iron to the mite via antibody mediated clearance, the result of host exposure to mite iron-binding homologues or because of a mite-induced antigenic change to host transferrin. Further investigation into the formation of these autoantibodies may provide insights into the importance of iron in scabies infections and the development and perseverance of S. scabiei infections in pigs. The specificity and sensitivity of the anti-transferrin response reinforces its potential in the diagnosis of scabies in pigs.

Primary and secondary experimental infestation of rabbits (Oryctolagus cuniculus) with Sarcoptes scabiei from a wild rabbit: factors determining resistance to reinfestation

Studies of sarcoptic mange and immunity are hampered by lack of mite sources and natural infestation models. We have investigated the clinical and pathological signs, specific IgG response and acquired immunity in naïve New Zealand White rabbits (Oryctolagus cuniculus) experimentally infested with Sarcoptes scabiei originally isolated from a clinically affected free-living European wild rabbit. Twenty rabbits were infested using two methods, direct contact for a 24 h period with a seeder rabbit simulating the natural process of infestation and application of a dressing holding approximately 1800 live mites on each hind limb (foot area) for a 24h period. Eight weeks post infestation, rabbits were treated with ivermectin and infestation cleared. Eight weeks later seventeen previously infested and four uninfested naïve controls were then re-exposed to the same S. scabiei variety using the same methods and followed for another 8 weeks. The progress of the disease was markedly more virulent in the animals infested by contact, indicating that the effective dose of mites managing to thrive and infest each rabbit by this method was higher. Nevertheless, infestation by contact resulted in partial protection to reexposure, rabbits developed high non-protective antibody titres upon reinfestation and presented severe clinical signs. However, rabbits reinfested by dressing developed lower IgG titres, and presented high levels of resistance to reinfestation, which might be due to induction of a strong local cellular response in the inoculation point that killed the mites and resulted in a lower mite effective dose, with subsequent reduced lesion development. Statistical analysis showed that sex, method of infestation and previous exposure are key factors determining the ability of rabbits to develop immunity to this disease. The rabbit-mange model developed will allow the further study of immunity and resistance to this neglected pathogen using a natural host system.

Antibody responses to Sarcoptes scabiei apolipoprotein in a porcine model: relevance to immunodiagnosis of recent infection

No commercial immunodiagnostic tests for human scabies are currently available, and existing animal tests are not sufficiently sensitive. The recombinant Sarcoptes scabiei apolipoprotein antigen Sar s 14.3 is a promising immunodiagnostic, eliciting high levels of IgE and IgG in infected people. Limited data are available regarding the temporal development of antibodies to Sar s 14.3, an issue of relevance in terms of immunodiagnosis. We utilised a porcine model to prospectively compare specific antibody responses to a primary infestation by ELISA, to Sar s 14.3 and to S. scabiei whole mite antigen extract (WMA). Differences in the antibody profile between antigens were apparent, with Sar s 14.3 responses detected earlier, and declining significantly after peak infestation compared to WMA. Both antigens resulted in >90% diagnostic sensitivity from weeks 8-16 post infestation. These data provide important information on the temporal development of humoral immune responses in scabies and further supports the development of recombinant antigen based immunodiagnostic tests for recent scabies infestations.

Variable performance of a human derived Sarcoptes scabiei recombinant antigen ELISA in swine mange diagnosis

The performance of an indirect ELISA test based on Sarcoptes scabiei var hominis recombinant antigen Ssλ20ΔB3 (rec-ELISA), to diagnose pig mange was investigated in 15 experimentally infected and non-infected pigs and 692 commercial pigs from 16 herds in southeast Spain. These latter animals included 6-7 month old fatteners (13 herds), 11-12 month old replacement sows (1 herd) and ≥24 month old breeding sows (7 herds). All pigs were examined for mites in ear skin scrapings and the presence of S. scabiei-associated macroscopic dermatitis; moreover, fatteners were also tested for antibodies against porcine viruses including: Aujeszky disease virus (ADV), swine influenza virus (SIV), type 2 porcine circovirus (PCV2) and porcine respiratory and reproductive syndrome virus (PRRSV). S. scabiei and chronic hyperkeratotic dermatitis were detected in breeding sows from 6 herds. Mite prevalence in other pigs was 83% in replacement sows, 0% in 7 fattener's herds and 3-82% in other fattener's herds. All fattener herds had pigs with acute hypersensitivity dermatitis and the percentage of affected pigs and lesion area was significantly greater in S. scabiei infected ones. Rec-ELISA relative optical densities (RODs) were greater in older than in young pigs, as well as in infected compared to non-infected pigs. However, RODs differed significantly between infected individuals, regardless of age and origin (commercial or experimental) and the herd prevalence of S. scabiei. Low repeatability between ELISA microtiter plates, suggesting variable specific antibody binding to antigen, are likely partly responsible for ROD variation. Other potential causes of variation were examined in fatteners using random effects logistic regression analysis, after defining a seropositivity threshold value with receiver-operating characteristics (ROC) analysis. The logistic model indicated that seropositivity was associated with large dermatitis areas and with the only herd with low PCV2 seroprevalence. Pigs with more extensive dermatitis may have older infections and more rec-ELISA detectable antibodies. The possibility that PCV2, a recognized immunosupressor, depresses antibody production against S. scabiei infection merits further attention. In summary, results indicate some potential of the studied rec-ELISA as a complementary tool for herd-level swine mange diagnosis, and that work to reduce internal and external sources of assay variation is essential.

Scabies: important clinical consequences explained by new molecular studies

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

Widespread exposure to Sarcoptes scabiei in wild European rabbits (Oryctolagus cuniculus) in Spain

Sarcoptic mange was recently described in the wild European rabbit (Oryctolagus cuniculus) in north-eastern Mediterranean Spain, the first such infection reported in this species anywhere in the world. This finding has created concern in conservationists and game managers given that an outbreak of mange after a translocation would have catastrophic consequences for naïve rabbit populations in other parts of Spain. A retrospective serosurvey using an 'in house' ELISA test based on the use of a recombinant antigen aimed at determining the rates of contact with Sarcoptes scabiei was carried out on sera from 966 rabbits collected between 1993 and 2010 in Spain. Antibodies were found in 13% of wild rabbits in 60% of the 53 areas surveyed, as well as in 16 of the 17 Spanish provinces and islands studied. Seropositive rabbits were found amongst the oldest samples analyzed and in all studied years. Antibodies were also detected in 36% of rabbits from the protected island of Dragonera, where rabbits have probably not been released since the 1970s. On Mallorca, where 89 rabbits were inspected for both lesions and antibodies, the prevalence of lesions (5.6%) was much lower than the seroprevalence (22.5%), indicating that rabbits often survive infection or that ELISA detects infected rabbits before they develop visible lesions. Seroprevalence was higher in areas with medium levels of rabbit abundance, no restocking and high rainfall. The results show that mange is widespread in rabbits and that the mite is not a recent introduction. Thus, sarcoptic mange could be considered as an enzootic disease in the wild rabbit and so prophylactic measures implemented during rabbit translocations are to be encouraged to avoid local outbreaks in naïve populations.

Characterisation of recombinant immunoreactive antigens of the scab mite Sarcoptes scabiei

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

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.

Identification and heterologous expression of a Sarcoptes scabiei cDNA encoding a structural antigen with immunodiagnostic potential

The mite Sarcoptes scabiei causes sarcoptic mange (or scabies), a disease of considerable human and veterinary significance. An S. scabiei cDNA clone of about 2 kb was isolated from a S. scabiei var. hominis expression library by immunological screening using blood serum from a naturally infected chamois (Rupicapra rupicapra). The nucleotide sequence of the identified cDNA contains an open reading frame of 1930 bp that encodes a 642 amino acid polypeptide. This polypeptide shows tandem repeats of a glycine-serine rich 20 residue sequence followed by a unique C-terminal glutamate rich 54 residue sequence. The cDNA or the deduced polypeptide did not show significant similarities to any of the sequences in the databases. A carboxyl-terminal fragment of this polypeptide (residues 380 to 642) was efficiently expressed in Escherichia coli as a fusion with Glutathione S-transferase and then was used to produce a specific antiserum. The antigen encoded by the cDNA was located at the integument of the mite's epidermis and the cavities surrounding its vital organs. Western blot analysis of mite extracts using the specific antiserum against the recombinant protein identified antigens larger that 60 kDa indicating that the isolated cDNA did not contain the full ORF. Moreover, we designed a diagnostic assay based on the carboxyl-terminal fragment of the antigen for the identification of infected animals.

Immunoblot analysis of IgG antibody response to Sarcoptes scabiei in swine

This study was performed to determine the frequencies and specificities of IgG antibodies binding to component of Sarcoptes scabiei extracts in swine with hypersensitive and chronic mange. The hypersensitive form is characterised by pruritus and the presence of small red papules over the flanks and belly. The chronic form is characterised by crusts, which contain large numbers of mites and are attached to the skin; the lesions are most commonly found on the internal pinna extending into the auditory canal. S. scabiei mite extract was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with subsequent immunoblotting. IgG-binding proteins were detected with individual sera from 30 hypersensitive and 21 chronically infected pigs; eight "Specific Pathogen Free" pigs were used as negative controls. Seven protein bands with molecular weights ranging from >220 to 30 Kilodalton (KDD) (>220, 218, 110, 80, 66, 52, 36 KDD) strongly bound with IgG antibodies; five out of these seven components (218, 110, 80, 66, 52 KDD) bound also with sera from negative pigs. There is a statistically significant difference in the antigenic recognition spectra between hypersensitive and chronically infected pigs; component of >220 KDD is more frequently recognized by chronically infected pigs (P=0.0006, chi(2)=11.74), in contrast component of 36 KDD is more frequently recognized by hypersensitive pigs (P=0.001, chi(2)=10). Our results clearly indicate there is a difference in the reactivity to antigenic peptides/proteins of S. scabiei mite between hypersensitive and chronically infected pigs, and revealed that only two antigens may be considered S. scabiei-specific and used for diagnostic purposes in swine.

Identification of auto-antigens in skin scrapings from scabies-infected pigs

Sarcoptes scabiei continues to cause major health and economic problems in a large range of animals and humans. Although the inflammatory response to the mite and its antigens is known to cause the main pathology, little work has been carried out on this response at the site of infection. This report presents an initial analysis of the proteins found in skin scrapings and their antigenic responsiveness in pigs. Skin scrapings and mite extracts were isolated from chronically infected sows while infected and uninfected sera were isolated from pigs with confirmed infections or mange-free pigs, respectively. Electrophoresis and sequencing confirmed the main components of both the skin and mite extracts to be serum proteins. Immunoblotting then suggested that transferrin was the major antigen recognised by pooled infected sera in the skin and the mite extracts. Immunoassays confirmed that a majority of infected pigs produced antibodies to transferrin while mange-free pigs did not. A pool of IgG from infected dogs was then used to isolate another antigen from pig skin scrapings which was shown to be haptoglobin. This was also found to induce high titres of antibody in infected pigs as compared with mange-free pigs. The use of albumin as a control antigen showed no reactivity in either group of sera. The finding of two iron-binding molecules as strong auto-antigens in pig scabies has implications for the importance of iron during this infection and may help to explain the persistence and magnitude of the host inflammatory response.

Crossreacting IgG antibodies against fox mite antigens in human scabies

Scabies continues to be an important parasitic disease of mammals. There remain, however, major gaps in the understanding of the human host immune response, and a simple diagnostic test is lacking. In contrast to human mites, red fox mites (Sarcoptes scabiei var. vulpis) can be collected easily and have been used, due to crossreactivity, for enzyme-linked immunosorbent assay (ELISA) studies in dogs and pigs. We wanted to investigate the possibility that crossreactivity might also exist for the human mite, and determined titers against fox mite antigens by ELISA in 41 patients with scabies. Specific IgG was significantly higher in patients with scabies than in healthy controls (P=0.01). The sensitivity was, however, only 48%, although it increased slightly during treatment (P=0.86). A positive correlation was also noted between disease duration and severity of infestation (r=0.5), with specific IgG titers increasing in parallel with severity of symptoms (P=0.01). Patients with symptomatic scabies for more than 4 weeks had furthermore significantly higher IgG titers than patients with a shorter duration of disease (P=0.007). In conclusion, these findings demonstrate IgG antibodies in human scabies that crossreact with fox mite antigens, thus encouraging the search for improved ELISAs with more specific mite antigens to produce a more sensitive detection system for scabies in humans.

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.

Paramyosin from the parasitic mite Sarcoptes scabiei: cDNA cloning and heterologous expression

The burrowing mite Sarcoptes scabiei is the causative agent of the highly contagious disease sarcoptic mange or scabies. So far, there is no in vitro propagation system for S. scabiei available, and mites used for various purposes must be isolated from infected hosts. Lack of parasite-derived material has limited the possibilities to study several aspects of scabies, including pathogenesis and immunity. It has also hampered the development of high performance serological assays. We have now constructed an S. scabiei cDNA expression library with mRNA purified from mites isolated from red foxes. Immunoscreening of the library enabled us to clone a full-length cDNA coding for a 102.5 kDa protein. Sequence similarity searches identified the protein as a paramyosin. Recombinant S. scabiei paramyosin expressed in Escherichia coli was recognized by sera from dogs and swine infected with S. scabiei. We also designed a small paramyosin construct of about 17 kDa that included the N-terminal part, an evolutionary variable part of the helical core, and the C-terminal part of the molecule. The miniaturized protein was efficiently expressed in E. coli and was recognized by sera from immunized rabbits. These data demonstrate that the cDNA library can assist in the isolation of important S. scabiei antigens and that recombinant proteins can be useful for the study of scabies.

Eradication of porcine sarcoptic mange within a health declared production model

The success of a large-scale eradication programme against sarcoptic mange was evaluated in piglet producing herds belonging to the health class LSO 2000. These farms are monitored to be free from sarcoptic mange, swine enzootic pneumoniae, swine dysentery and progressive atrophic rhinitis. The local veterinarians were instructed to eradicate sarcoptic mange from the herds by 2 ivermectin injections 14 days apart or 3 treatments with phoxim pour-on 6 days apart before the farms were able to join the health class. The study consisted of a questionnaire administered to the farmers, farm visits and follow-ups associated with the regular control of the health class. A questionnaire was sent to all of the 379 accepted farrowing farms. Altogether 323 farmers had initiated an eradication programme at least 7 months before the questionnaire was distributed and 96% of them believed that the mange eradication programme had been successful. In most of the successful herds (90%), the local veterinarian had treated the animals by the recommended methods, and the majority of the farmers (88%) had cleaned and sprayed the pens with insecticides on the days of treatment. Three out of the 7 unsuccessful farms had employed methods other than those recommended. Twenty-five herds were randomly selected for an intensified control. The rubbing index was < or = 0.1 in all herds visited, indicating freedom from mange. Sows or gilts, 15-20 animals per farm, were skin scraped and no Sarcoptes scabiei was found. The same animals were blood sampled and serum antibodies to S. scabiei were measured by an indirect ELISA. All except 1 farm had low optical density (OD) values in most of the samples. The owner of that farm had become uncertain about the mange status of the herd and had recently retreated all animals with acaricides. The number of complaints about mange in the finishing units buying health class feeder pigs was low. The study demonstrates that it is possible to run an eradication programme against sarcoptic mange, in which a large number of farmers together with their veterinarians participate. It is possible to eradicate mange not only at the herd but also at the population level. The ELISA test employed proved to be a possible tool to monitor the efficacy of mange-eradication programmes.

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.

Validation of ELISAs for the detection of antibodies to Sarcoptes scabiei in pigs

An Enzyme-linked ImmunoSorbent Assay (ELISA) was developed for the detection of antibodies to Sarcoptes scabiei. This 'Animal Health Service'-ELISA (AHS-ELISA) was compared with a commercial test (Checkit(R) Sarcoptest) using experimental and field sera. The experimental study was a contact infestation experiment. Eighty piglets were randomly divided between the experimental and control group. After introduction of three Sarcoptes scabiei var. suis infested pigs in the experimental group, both groups were monitored by determining scratching indices, taking ear scrapings and blood samples in Weeks 0, 2, 4, 6, 8, 12 and 16. Four pigs in the control group were immunised with either Dermatophagoides pteronyssinus (Dp) antigens (n=2), or Acarus siro (As) antigens (n=2). In the control group all (non-immunised) pigs were negative in all tests. In the experimental group only slightly elevated scratching indices were observed, with a maximum in Week 8. After 2 weeks for the first time an ear scraping was positive (2.5%). In Week 8 the highest number of positive ear scrapings were found (25.0%). Positive results in the Sarcoptest were first obtained in Week 12 (10.5% positive), while eventually 29.0% of the finishing pigs were positive after 16 weeks. The AHS-ELISA first detected a serological response after 6 weeks (5. 0% positives), increasing until after 16 weeks a large proportion (74.2%) of the finishing pigs were seropositive, making the AHS-ELISA the most sensitive test. In the AHS-ELISA one As-immunised pig remained seronegative, but the other hyper-immunised pigs crossreacted. In the Sarcoptest, only Dp-immunised pigs had elevated Optical Densities (OD's) albeit below the cut-off level. Although hyper-immunisation is not a representation of field conditions, it cannot be excluded that the AHS-ELISA is not 100% specific.Field samples were taken from 20 sows in 30 herds, classified as mange-free, suspect, or infested. On a herd level there was high agreement among the ELISAs. Both serological tests were suitable to distinguish mange-free herds from infested herds. In one infested herd the decline of maternal antibody in piglets was studied by sampling 40 piglets from 20 different litters. The lowest average OD using the AHS-ELISA was found at 5 weeks of age, followed by a significant increase at 7 weeks. The average OD with the Sarcoptest was at a minimum level at 3 weeks, but no increase was found later. For screening of herds, interference of maternal antibodies is avoided by sampling at an age of 7 weeks or older.

Eradication of sarcoptic mange from a Belgian pig breeding farm with a combination of injectable and in-feed ivermectin

Sarcoptes scabiei var suis was eradicated from a Belgian pig farm by using a combination of injections of ivermectin and ivermectin in the feed. The detection of mites in ear scrapings, and calculations of an average dermatitis score and a scratching index were used to evaluate the mange status of the pigs before and after the treatment. Before the treatment 28 per cent of ear scrapings of finishers were positive for the presence of mites, their average dermatitis score (ADS) was 0.92 and their scratching index was 2.0. There was a significant decrease in all three measurements during the year after the treatment, and one year after treatment, no mites were found in the ear scrapings; the ADS of the finishers was 0.31 and their scratching index was 0.16. Adult animals were negative for the presence of mites at all times, the ADS was below the cut-off level before and after treatment, and the scratching index decreased after treatment There was an economic improvement among the breeding sows and the fattening pigs. The feed consumption of the sows decreased by 5 per cent; rebreeding decreased by 4.55 per cent; average litter size increased by 0.33 live piglets born per litter and the farrowing index increased by 0.075 litters per sow per year. As a result, the production index increased by 1.34 more piglets weaned per sow per year. There was an immediate improvement in feed conversion during the five months after the treatment. The costs of the treatment were recovered within 3.7 months.