Sheep Scab Mite Research Articles

In silico identification of neurohormones and neuropeptides and their G protein-coupled receptors in the sheep scab mite Psoroptes ovis: potential targets for alternative control strategies

ABSTRACT The genome of the sheep scab mite, Psoroptes ovis, was analysed for the presence of neuropeptide and neurohormone precursors and their G protein-coupled receptors (GPCRs). Many of these showed significant similarities to those known or predicted from other Acaridae and also insect species. Similarities to orthologous precursors and receptors from the sheep Ovis aries, host for P. ovis, were also evaluated. The roles of neuropeptides and neurohormones in the control of behavioural and physiological processes such as osmoregulation, reproduction, growth and development are discussed. The GPCRs for these neuropeptides and neurohormones offer potential targets for the development of next-generation acaricides. Modification of normal receptor function by new chemistries that either block or over-stimulate the GPCRs can result in the death of the mite or alter its normal development and reproductive ability thereby suppressing populations. This work provides the information required to select potential GPCR targets in P. ovis for future development of new acaricides.

Screening for antibodies against the sheep scab mite (Psoroptes ovis) Pso o 2 antigen in experimentally infested Swifter sheep may fail to identify affected animals

Sheep scab, caused by Psoroptes ovis mites, represents a significant threat to sheep health and welfare. Infestations are diagnosed by parasite identification in skin scrapings, and more recently with a commercial ELISA against serum antibodies to the Pso o 2 mite allergen. However, little is known about the performance of the ELISA in non-UK sheep populations. In this study, six Swifter sheep were experimentally infested with P. ovis. Lesion sizes were monitored and serum IgG against Pso o 2 and the novel Pso-EIP-1 antigens were measured by ELISA. Although all sheep showed signs of infestation, serum from two animals failed to react with Pso o 2. However, they did react to Pso-EIP-1. This indicates that cases of sheep scab in (Swifter) sheep may remain undetected using the Pso o 2 ELISA, which may have implications for routine screening of non- UK sheep breeds.

Multiple resistance to macrocyclic lactones in the sheep scab mite Psoroptes ovis

The astigmatid mite Psoroptes ovis (Acari: Proroptidae) causes the highly contagious and debilitating ovine disease, sheep scab. This ectoparasitic infection has a high economic and animal welfare impact on British sheep farming. Following recent work demonstrating resistance of Psoroptes mites to moxidectin, a widely used macrocyclic lactone (ML) treatment for scab, the current study compared the toxicity of three of the commonly administered macrocylic lactone therapeutic treatments (moxidectin, ivermectin and doramectin) to P. ovis from outbreak populations that had appeared unresponsive to treatment. These outbreak populations were from Wales and south west England. The data presented demonstrate that there is resistance to all three available ML compounds in populations of Psoroptes mites. However, considerable variation in response suggested that resistance alone was not responsible for the reported lack of efficacy in all of the submitted cases; lack of response in others may be associated with inappropriate treatment application or management. These data highlight the importance of the appropriate use of these compounds to manage national scab incidence at levels that are consistent with acceptable animal welfare standards, while attempting to reduce the development and spread of resistance.

First evidence of resistance to macrocyclic lactones in Psoroptes ovis sheep scab mites in the UK

Ovine psoroptic mange (sheep scab) is an infection of substantial economic and animal welfare concern in the UK. Its prevalence has increased rapidly over the last 20 years and management...

Der f 35: An MD-2-like house dust mite allergen that cross-reacts with Der f 2 and Pso o 2.

Dermatophagoides farinae is a source of airborne house dust mite (HDM) allergens. We elucidated IgE-reactive allergens from D.farinae by two-dimensional immunoblotting-based allergenome analysis, and identified one new allergen, named Der f 35, that possesses IgE-binding capacity comparable to that of Der f 2. The aim of this study was to clarify the allergenic capacity of new HDM allergen Der f 35. We cloned der f 35 from D.farinae mRNA and produced recombinant Der f 35 in Escherichia coli. The IgE-binding capacity of Der f 35 and its cross-reactivity with group 2 allergens from D.farinae and Psoroptes ovis were determined by enzyme-linked immunosorbent assay (ELISA) and ELISA inhibition assays, respectively. The deduced amino acid sequence for der f 35, which possesses the MD-2-related lipid-recognition domain, showed higher identity with group 2 allergens from P.ovis (61.5%) and Blomia tropicalis (50.7%) than with Der f 2 (40.8%). Der f 35 showed IgE-binding frequencies of 77.5% (31/40) for the native form upon allergenome analysis and 51.4% (18/35) for recombinant structure by ELISA. Der f 35 showed cross-reactivity with Der f 2 and Pso o 2 in reaction with HDM-allergic patients' IgE by ELISA inhibition assay. Der f 35 is a candidate major allergen from D.farinae, which is more similar to group 2 allergens from sheep scab mite and storage mites. Der f 35 could be responsible for the cross-reactivity among group 2 mite allergens.

Primary screen for potential sheep scab control agents

The efficacy of potential acaricidal agents were assessed against the sheep scab mite Psoroptes ovis using a series of in vitro assays in modified test arenas designed initially to maintain P. ovis off-host. The mortality effects of 45 control agents, including essential oils, detergents, desiccants, growth regulators, lipid synthesis inhibitors, nerve action/energy metabolism disruptors and ecdysteroids were assessed against adults and nymphs. The most effective candidates were the desiccants (diatomaceous earth, nanoclay and sorex), the growth regulators (buprofezin, hexythiazox and teflubenzuron), the lipid synthesis inhibitors (spirodiclofen, spirotetramat and spiromesifen) and the nerve action and energy metabolism inhibitors (fenpyroximate, spinosad, tolfenpyrad, and chlorantraniliprole).

Comparative immune responses against Psoroptes ovis in two cattle breeds with different susceptibility to mange.

The sheep scab mite, Psoroptes ovis, is a major problem in the beef cattle industry, especially in Belgian Blue (BB) cattle. This breed is naturally more predisposed to psoroptic mange but reasons for this high susceptibility remain unknown. Different immune responses could be a potential cause; thus in this study, the cutaneous immune response and in vitro cellular immune response after antigen re-stimulation were examined in naturally infested BB. Cytokine production in the skin and in circulating re-stimulated peripheral blood mononuclear cells (PBMC) demonstrated a mixed pro-inflammatory Th2/Th17 profile, with transcription of IL-4, IL-13, IL-6 and IL-17. Strong IL-17 up-regulation in the skin of BB was associated with an influx of eosinophils and other immune cells, potentially leading towards more severe symptoms. Virtually no changes in cutaneous IFN-γ transcription were detected, while there was substantial IFN-γ up-regulation in re-stimulated PBMC from infested and uninfested animals, potentially indicating a role of this pro-inflammatory cytokine in the innate immune response. In Holstein–Friesian (HF) cattle, generally more resistant to P. ovis infection, a largely similar immunologic response was observed. Differences between HF and BB were the lack of cutaneous IL-17 response in infested HF and low transcription levels of IFN-γ and high IL-10 transcription in re-stimulated PBMC from both infested and uninfested animals. Further research is needed to identify potential cell sources and biological functions for these cytokines and to fully unravel the basis of this different breed susceptibility to P. ovis.

Ectoparasites of medical and veterinary importance: drug resistance and the need for alternative control methods.

Despite multiple attempts at eradication, many ectoparasites of humans and domestic livestock remain a persistent problem in the modern world. For many years, a range of pesticide drugs including organophosphates, organochlorides and synthetic pyrethroids provided effective control of these parasites; but intensive use of these drugs has led to the evolution of resistance in many target species. This paper aims to review the effectiveness of current control methods and discuss potential alternatives for the long term sustainable control of ectoparasites. Important medical ectoparasites such as scabies mites, head lice and bed bugs present a significant public health problem, and so adequate control methods are essential. Ectoparasites of domestic livestock and farmed fish (for example sheep scab mites, poultry mites and sea lice) are also of concern given the increasing strain on the world's food supply. These parasites have become resistant to several classes of pesticide, making control very difficult. Recently, an increasing amount of research has focussed on alternative control methods such as insect growth regulators, biological control using essential oils or fungi, as well as vaccine development against some ectoparasites of medical and veterinary importance. Drug resistance is prevalent in all of the ectoparasites discussed in this review. A wide variety of alternative control methods have been identified, however further research is necessary in order for these to be used to successfully control ectoparasitic diseases in the future.

Transcriptomic Analysis of Circulating Leukocytes Reveals Novel Aspects of the Host Systemic Inflammatory Response to Sheep Scab Mites

Infestation of ovine skin with the ectoparasitic mite Psoroptes ovis results in the development of a rapid cutaneous inflammatory response, leading to the crusted skin lesions characteristic of sheep scab. To facilitate the identification of novel diagnostic and therapeutic targets, a better understanding of the host-parasite relationship in sheep scab is essential. Although our knowledge of the host's local cutaneous inflammatory response to sheep scab has increased in recent years, we still know relatively little about the mechanisms of this response at the systemic level. This study used a combined network and pathway analysis of the in vivo transcriptomic response of circulating leukocytes to infestation with P. ovis, during a 6 week period. Network graph analysis identified six temporally-associated gene clusters, which separated into two distinct sub-networks within the graph, representing those genes either up or down-regulated during the time course. Functional and pathway analysis of these clusters identified novel insights into the host systemic response to P. ovis infestation, including roles for the complement system, clotting cascade and fibrinolysis. These analyses also highlighted potential mechanisms by which the systemic immune response to sheep scab can influence local tissue responses via enhanced leukocyte activation and extravasation. By analysing the transcriptomic responses of circulating leukocytes in sheep following infestation with P. ovis, this study has provided key insights into the inflammatory response to infestation and has also demonstrated the utility of these cells as a proxy of events occurring at local tissue sites, providing insight into the mechanisms by which a local allergen-induced inflammatory response may be controlled.

Intestinal proteases of free-living and parasitic astigmatid mites

Among arthropod pests, mites are responsible for considerable damage to crops, humans and other animals. However, detailed physiological data on these organisms remain sparse, mainly because of their small size but possibly also because of their extreme diversity. Focusing on intestinal proteases, we draw together information from three distinct mite species that all feed on skin but have separately adapted to a free-living, a strictly ecto-parasitic and a parasitic lifestyle. A wide range of studies involving immunohistology, molecular biology, X-ray crystallography and enzyme biochemistry of mite gut proteases suggests that these creatures have diverged considerably as house dust mites, sheep scab mites and scabies mites. Each species has evolved a particular variation of a presumably ancestral repertoire of digestive enzymes that have become specifically adapted to their individual environmental requirements.

Development of a cDNA microarray for the measurement of gene expression in the sheep scab mite Psoroptes ovis

BackgroundSheep scab is caused by the ectoparasitic mite Psoroptes ovis which initiates a profound cutaneous inflammatory response, leading to the development of the skin lesions which are characteristic of the disease. Existing control strategies rely upon injectable endectocides and acaricidal dips but concerns over residues, eco-toxicity and the development of acaricide resistance limit the sustainability of this approach. In order to identify alternative means of disease control, a deeper understanding of both the parasite and its interaction with the host are required.MethodsHerein we describe the development and utilisation of an annotated P. ovis cDNA microarray containing 3,456 elements for the measurement of gene expression in this economically important ectoparasite. The array consists of 981 P. ovis EST sequences printed in triplicate along with 513 control elements. Array performance was validated through the analysis of gene expression differences between fed and starved P. ovis mites.ResultsSequences represented on the array include homologues of major house dust mite allergens and tick salivary proteins, along with factors potentially involved in mite reproduction and xenobiotic metabolism. In order to validate the performance of this unique resource under biological conditions we used the array to analyse gene expression differences between fed and starved P. ovis mites. These analyses identified a number of house dust mite allergen homologues up-regulated in fed mites and P. ovis transcripts involved in stress responses, autophagy and chemosensory perception up-regulated in starved mites.ConclusionThe P. ovis cDNA microarray described here has been shown to be both robust and reproducible and will enable future studies to analyse gene expression in this important ectoparasite.

Infestation of sheep withPsoroptes ovis, the sheep scab mite, results in recruitment of Foxp3+T cells into the dermis

Regulatory T cells (Tregs) play a central role in maintenance of immune homeostasis by controlling harmful immune responses to inappropriate antigens and are thought to play a key role in modulating hypersensitivity reactions. Infestation of sheep with Psoroptes ovis results in a pronounced cutaneous hypersensitivity-type response, which appears to be crucial for mite survival. We hypothesize that (i) Tregs are involved in sheep scab lesions and (ii) Treg responses may crucially affect lesion development and subsequent mite survival. Foxp3 is a key transcription factor required for generation and maintenance of Tregs in rodents and humans, and is the most widely used marker for Tregs in these species. In this study, we sequence ovine foxp3 and show that it exhibits a high degree of homology with foxp3 from other species. Using a validated immunohistochemical staining technique, we demonstrate that infestation of sheep with P. ovis results in an influx of Foxp3(+) T cells into the skin. Future work will investigate the regulatory function of ovine Foxp3(+) T cells and determine whether the quality of the Treg response to P. ovis plays a role in individual susceptibility to the mite.

Molecular characterization, expression and localization of a peroxiredoxin from the sheep scab mite,Psoroptes ovis

The sheep scab mite, Psoroptes ovis, induces an intensely pruritic exudative dermatitis which is responsible for restlessness, loss of appetite and weight loss. Within the first 24 h of infection, there is a rapid inflammatory influx of eosinophils and apoptosis of the keratinocytes at the site of infection. The former cell type is capable of a sustained respiratory burst, toxic products of which may directly damage the mite and also contribute to lesion formation. Analysis of a P. ovis expressed sequence tag (EST) database identified a number of antioxidant enzyme-encoding sequences, including peroxiredoxin (thioredoxin peroxidase EC 1.11.1.15), all of which may help the mite endure the potentially toxic skin environment. A full length sequence encoding Po-TPx, a protein of 206 amino acids which showed high homology to a peroxiredoxin from the salivary gland of the tick Ixodes scapularis, was amplified from P. ovis cDNA. Recombinant Po-TPx was expressed in bacteria and antiserum to this protein was used to localize native Po-TPx in mite sections. Peroxiredoxin was localized, amongst other sites, to a subpharyngeal region in mite sections. The recombinant protein was recognized by sera from sheep infested with the mite suggesting that it may be secreted or excreted by the mite and interact with the host immune response.

Effects of sheep fleece washings on the germination and growth of Beauveria bassiana

The development of biopesticides against ectoparasites must take into account the effect that an animal host’s secretions and host associated micro-organisms may have on the viability of the applied agent. In this study, the effects of secretions washed from the pelt of sheep on the viability and growth of the fungal pathogen Beauveria bassiana, were assessed. The fungal isolate had been obtained from the parasitic sheep scab mite Psoroptes ovis. It was added to 0.05% Tween 80 in which sheep fleece had been washed up to six times, to ascertain whether successive washings had any effect on the viability of conidia over 6 days. The effects of sterile and non-sterile washings on viability and growth were also investigated. Results indicated that substances in the sheep fleece may cause a significant reduction in the viability of conidia. Viability was linked to the number of times the sheep pelt had been washed in the Tween, with conidia incubated in the first wash from the sheep pelt showing a significantly greater decrease in viability compared to those incubated in the sixth wash. Viability was not linked to the sterility of the washes, although there was a significant difference between length of germ tube growth from viable conidia in sterile and non-sterile washings.

Psoroptes ovis: Identification of vaccine candidates by immunoscreening

Serum from successful vaccine trials against the sheep scab mite, Psoroptes ovis, was used to immunoscreen a cDNA library constructed from mixed-stage and gender P. ovis to identify potential recombinant vaccine candidates. Immunodominant recombinant proteins recognised by IgG in these sera were selected for further analysis. Two candidates were identified in this way; a catchin-like protein (CLP) and a novel mu class glutathione S-transferase (GST). Both candidates were expressed in bacteria as recombinant proteins, the GST as an active enzyme, and combined with four other recombinant allergens in a multi-component recombinant vaccine. Strong serum IgG responses were induced in sheep against each of the components of the recombinant vaccine, however, the protective efficacy of the vaccine could not be determined because of variability in the establishment of a challenge infection.

Maintaining Psoroptes ovis (Acari: Psoroptidae) off-host in the laboratory

Feeding and maintaining sheep scab mites off-host is an important step towards achieving a safer, environmentally-friendly means of controlling sheep scab disease. The test arena developed by Thind and Muggleton (Exp Appl Acarol 22:543-552, 1998) has been adapted for feeding and maintaining Psoroptes ovis off-host. The test arenas are simple to construct and use, and escape-proof to all stages of mites. The performance of the test arenas was assessed by determining the survival of the scab mites at 33 and 36 degrees C and >95% r.h. on different diets. With this test arena the best reported mean survival of 10.3 days was achieved with both females and nymphs at a temperature of 33 degrees C on a diet of sheep serum; the mean maximum survival of females at these conditions was 18.8 days, which is at least a threefold improvement on previous reports. With further development it may be possible to adapt the test arena for assessing both slow and fast acting agents for controlling sheep scab.

Control of the sheep scab mite Psoroptes ovis in vivo and in vitro using fungal pathogens

As part of a research programme designed to identify biological agents for the control of sheep scab, the pathogenicity of the fungus Metarhizium anisopliae to Psoroptes mites in the presence of sheepskin and wool was examined in the laboratory. No inhibitory effects of skin and wool were observed and high levels of infection were recorded. Subsequently the pathogenicity of formulations of both M. anisopliae and Beauveria bassiana to Psoroptes ovis was studied in vivo. For this, 36 batches of 20 adult female Psoroptes mites were confined in 25 mm diameter chambers which were attached to the backs of 6 scab-naive sheep. In some treatments, mites were exposed to the fungal pathogens for 48 h in vitro prior to being placed on the host, while other treatments involved mites with no prior exposure placed directly onto the skin of a host treated with a fungal pathogen. After 48 h on the host, mites were removed, incubated individually and all fungal infections were recorded. Fungal infection was observed in all treatments, except untreated controls. However, B. bassiana infected a significantly greater number of mites than M. anisopliae with all the formulations examined. Infection rates were highest when mites were exposed to dry conidia (>90%) and lowest with M. anisopliae in diatomaceous earth. Overall, the infection rate was not affected by whether or not the mites were given prior exposure to the conidia, before being placed on the sheep. The results demonstrate that Psoroptes mites can become infected by entomopathogenic fungi on the skin of sheep and provides a first demonstration of the potential of this technology for the control of sheep scab.

Stimulation of the In Vitro Migration of Ovine Eosinophils by Factors Derived from the Sheep Scab Mite, Psoroptes ovis

The ectoparasitic astigmatid mite Psoroptes ovis causes sheep scab, a highly contagious, severe allergic dermatitis associated with damage to the fleece and hide, loss of condition and occasional mortality. The scab lesion is characterized by a massive infiltration of eosinophils that begins very rapidly after infection. This paper reports the finding that mite-derived factors directly enhance the migration of ovine eosinophils in vitro. Significant (p < 0.01) and dose-dependent (r = 0.972 +/- 0.018 (SD)) activity was initially identified in whole mite extracts, by comparison with medium controls in an assay based on modified Boyden chambers and ovine bone marrow target cells. Similar pro-migratory activity (p < 0.005; r = 0.928 +/- 0.069 (SD)) was detected in washes containing mite excretory/secretory material. By direct comparison with migration ratios (n = 3) for defined chemotactic (rmeotaxin = 3.430 +/- 0.360 (SD)) and chemokinetic (rminterleukin-5 = 0.982 +/- 0.112 (SD)) stimuli it was determined that the activity in both mite extracts (0.992 +/- 0.038 (SD)) and mite washes (0.969 +/- 0.071 (SD)) was chemokinetic. Subsequent experiments (n = 3) in which live mites were incorporated directly into the in vitro assay system indicated that they produced factors that significantly (p < 0.001) enhanced eosinophil migration to a degree directly related to mite numbers (r = 0.993 +/- 0.005 (SD)). The identity of the factor(s) responsible is uncertain, but their presence suggests that mites may be capable of directly activating eosinophils in vivo, and raises the possibility that mites could directly influence, perhaps even initiate, the rapid early tissue eosinophilic response observed in experimental sheep scab infections.

Molecular characterization, expression and localization of tropomyosin and paramyosin immunodominant allergens from sheep scab mites (Psoroptes ovis)

cDNAs encoding the immunodominant allergens tropomyosin and paramyosin were amplified from RNA extracted from the sheep scab mite Psoroptes ovis. The tropomyosin cDNA contained an open reading frame (ORF) of 852 bp which encoded a predicted protein with 98% and 97% identity to the house dust mite allergens Der f 10 and Der p 10 respectively. The complete paramyosin ORF generated by RT-PCR was 2625 bp in length and encoded an 875aa predicted protein of 102.6 kDa with 97%, 95% and 89% identity to the paramyosins of Dermatophagoides pteronyssinus (Der p 11), Sarcoptes scabiei and Blomia tropicalis (Blo t 11) respectively. Full length tropomyosin and truncated and full-length paramyosin were expressed as recombinant proteins. IgG and IgE in sera from sheep with a 6-week duration primary infestation of P. ovis did not detect either full-length or truncated recombinant paramyosin. IgG in both infested and naïve sheep sera detected recombinant tropomyosin, suggesting cross-reactivity to tropomyosin and to other invertebrate species to which the sheep may have been exposed. Staining with antibodies directed against tropomyosin and paramyosin was observed throughout sections of P. ovis. Staining was especially prevalent in the anterior sections of the mites, possibly associated with locomotory muscles in this region.

Immune responses to Staphylococcus aureus and Psoroptes ovis in sheep infected with P. ovis — the sheep scab mite

In sheep, lesions caused by Psoroptes ovis, the sheep scab mite, may become colonized by Staphylococcus aureus. The present study compares clinical signs, lesional area and the immune response to P. ovis and S. aureus in P. ovis-infested sheep with and without secondary S. aureus infection. No differences were detected in the clinical signs or lesional areas in the S. aureus-positive and -negative sheep. However, 6 weeks after infestation an IgG but not IgE isotype antibody response to S. aureus was detected in the S. aureus-positive but not the S. aureus-negative group of sheep. This response targeted S. aureus antigens with molecular weights of approximately 36, 38, 50 and 65 kDa. In addition, 6 weeks after infestation an IgE response to P. ovis was detected in the S. aureus-positive but not the S. aureus-negative group of sheep.