Sheep scab: the disease, pathogenesis and control

The tales of contradiction: A thematic analysis of British sheep farmers' perceptions of managing sheep scab in their flocks

Sheep scab is endemic in Great Britain with an estimated national herd-level prevalence of 10.9% from a surveyed population of sheep farms. Previous studies have investigated how sheep farmers manage sheep scab on their farms in Great Britain, but there have not been any qualitative studies investigating sheep farmers perceptions on the roles different stakeholders have in the management of sheep scab. This qualitative study aims to explore how sheep farmers perceive their role and the different stakeholders' roles in the management of sheep scab, and how they would like sheep scab to be managed going forward. Semi-structured interviews were conducted with 43 sheep farmers from England, Scotland, and Wales. The data were analysed using reflexive thematic analysis, through the theoretical lens of Foucault's notion of 'biopower'. Two themes were generated: 'The feeling of powerlessness leads to a need of rules and regulations', with sub-themes: 'The need for governmental rules and regulations' and 'The need for rules and regulation at livestock markets', and 'An apparent lack of sheep scab surveillance', with sub-themes: 'The farmers perceive that the veterinarians have control over surveillance' and 'The farmers have control over surveillance on their farms'. In the first theme, the respondents suggested that more rules and regulations to control the management of sheep scab was required. This included reinstating of sheep scab as a notifiable disease in England and Wales, as well as more regulations at livestock markets to prevent the trading of infested sheep; both of which would subject the farmers to regulatory power mechanisms. The second theme centred around who has the control of surveillance on the farms. Most of the respondents perceived that the veterinarians had knowledge and expertise of the local area on sheep scab, which they were able to relay to the farmers. Thus, veterinarians exerted disciplinary power by creating 'docile' bodies. However, it also appeared that veterinarians were not regularly called onto farms. Although disciplinary power flows through the interactions between the farmer and veterinarian, the techniques currently used are not always having their desired effect. The study demonstrated that how sheep farmers want sheep scab to be managed is, at times, conflicting and contradictory, which highlights the complexity of sheep scab as a disease to manage.

Repeated Cross-Sectional Survey of Ectoparasites in Sheep from Central Tunisia: Does Low Prevalence Indicate Good Hygiene or Resistance to Ectoparasites?

Sheep ectoparasites such as chewing lice, fleas and ticks are serious constraints to sheep productivity and are the cause of skin lesions in animals that decrease their market value. This study aims at investigating the ectoparasite fauna infesting small ruminants in the district of Sidi Bouzid (central Tunisia). A total of 1243 Barbarine and Queue Fine de l'Ouest (QFO) sheep were examined every two months for one year. Of the total animals examined, 74 were infested by at least 1 parasite group (5.95%). Three ectoparasite groups were identified as Psoroptes ovis (0.48%; 6/1243), ticks (5.3%; n = 66/1243) and one specimen of Ctenocephalides canis (0.08%; n = 1/1243). The most abundant tick among the 358 specimens was Rhipicephalus sanguineus sensu lato (n = 337; 94.1%), followed by Hyalomma impeltatum (n = 7/358; 1.9%), H. dromedarii (n = 7/358; 1.9%), H. excavatum (n = 5/358; 1.4%) and only two specimens of H. scupense (n = 2/358; 0.55%). The sheep herds showed low infestation prevalence by ectoparasite over the year, with a significant difference according to the seasons (p < 0.05). A higher infestation prevalence was recorded in March (14.36%). Barbarine sheep breed showed significantly higher infestation prevalence (16.8%) compared to QFO (0.8%) (p < 0.01). There were no differences in infestation prevalence according to sex of the animal or age groups. Knowledge of the ectoparasite population harboured by sheep, its activity dynamics and risk factors is required to develop effective ectoparasite control options. The low prevalence of ectoparasite infestation in sheep reported here may be due to possible genetic resistance or simply to successful hygiene measures implemented by farmers.

Methods to develop and evaluate attitudinal scales to measure farmer perceptions: Using sheep scab as an example

There is limited information on the attitudes and opinions of British sheep farmers when preventing and managing sheep scab in their flocks. Attitudes are examples of latent traits, which are not directly observable. They must be measured indirectly which can be achieved using measurement scales. Attitudinal measurement scales are used frequently in research, but are seldom evaluated prior to use, particularly in veterinary research. Therefore, the aim of this study was to identify and assess latent traits which influence the control of sheep scab with the use of exploratory factor analysis, and then further evaluate these factors with the use of item response theory to determine how they perform as scales. An online survey was completed by 726 British sheep farmers during October 2021 (725 useable responses), which included a section with 37 belief statements related to the opinions and attitudes of sheep farmers around the management of sheep scab. These belief statements were developed and adapted from previous research. During the analysis, they were subjected to exploratory factor analysis, which suggested that the scales performed reasonably well. The scales were then evaluated further by item response theory. The graded response models for each attitudinal scale were assessed by graphical evaluation. They demonstrated that the scales were able to distinguish those respondents with low perceptions of control, responsibility, and trust, and those who had high perceptions of luck. This study provides insights into some of the factors influencing the management of sheep scab, and how well these scales perform. Additionally, it further highlights the importance of evaluating attitudinal scales for use in research, and that exploratory factor analysis alone does not provide enough information on how well they perform.

Macrophage Migration Inhibitory Factor in Psoroptes ovis: Molecular Characterization and Potential Role in Eosinophil Accumulation of Skin in Rabbit and Its Implication in the Host-Parasite Interaction

Psoroptes ovis, a common surface-living mite of domestic and wild animals worldwide, results in huge economic losses and serious welfare issues in the animal industry. P. ovis infestation rapidly causes massive eosinophil infiltration in skin lesions, and increasing research revealed that eosinophils might play an important role in the pathogenesis of P. ovis infestation. Intradermal injection of P. ovis antigen invoked massive eosinophil infiltration, suggesting that this mite should contain some relative molecules involved in eosinophil accumulation in the skin. However, these active molecules have not yet been identified. Herein, we identified macrophage migration inhibitor factor (MIF) in P. ovis (PsoMIF) using bioinformatics and molecular biology methods. Sequence analyses revealed that PsoMIF appeared with high similarity to the topology of monomer and trimer formation with host MIF (RMSD = 0.28 angstroms and 2.826 angstroms, respectively) but with differences in tautomerase and thiol-protein oxidoreductase active sites. Reverse transcription PCR analysis (qRT-PCR) results showed that PsoMIF was expressed throughout all the developmental stages of P. ovis, particularly with the highest expression in female mites. Immunolocalization revealed that MIF protein located in the ovary and oviduct of female mites and also localized throughout the stratum spinosum, stratum granulosum, and even basal layers of the epidermis in skin lesions caused by P. ovis. rPsoMIF significantly upregulated eosinophil-related gene expression both in vitro (PBMC: CCL5, CCL11; HaCaT: IL-3, IL-4, IL-5, CCL5, CCL11) and in vivo (rabbit: IL-5, CCL5, CCL11, P-selectin, ICAM-1). Moreover, rPsoMIF could induce cutaneous eosinophil accumulation in a rabbit model and increased the vascular permeability in a mouse model. Our findings indicated that PsoMIF served as one of the key molecules contributing to skin eosinophil accumulation in P. ovis infection of rabbits.

A survey of British sheep farmers: Practices, opinions and knowledge surrounding the management of sheep scab

Ovine psoroptic mange (commonly known as sheep scab) is, arguably, one of the most important ectoparasitic diseases of sheep in the UK. Although research has been conducted on the practices and knowledge of British sheep farmers regarding the management of sheep scab, recent data is limited. During October 2021 an online survey was completed by 725 British sheep farmers. Most respondents farmed in England (63.0%, 457/725), followed by Wales (20.6%, 149/725) and Scotland (16.4%, 119/725). Over half (53.0%, 384/725) of the respondents had experienced sheep scab in their flocks before, and 38.3% (147/384) of respondents experienced sheep scab twice or more in the previous ten years. The estimated prevalence of sheep scab from these surveyed farmers was 10.9% (79/725). Of the farmers who had experienced sheep scab before, only 36.2% (139/384) reported using skin scrapes and 12.5% (48/384) reported using blood tests for diagnosis. Over three-quarters of farmers quarantined all new sheep (76.6%; 498/650), but fewer quarantined returning sheep (28.6%; 83/290). Many of the respondents (43.7%, 252/577) did not quarantine new sheep for the suggested minimum 21 days. In addition, only 53.0% (384/725) of respondents answered all three of the knowledge questions regarding sheep scab correctly. The analysis illustrates that there is scope to improve the use of diagnostics, which suggests that misdiagnosis of sheep scab may be high and thus inappropriate treatments may be used, or treatments may not be used at all. It also demonstrated that there is scope for improvement in farmers' knowledge regarding sheep scab, particularly that sheep scab could be detected via a blood test and that the disease could present without visible signs. Our results further support that sheep scab is a large-scale endemic issue, potentially with an increasing prevalence in Great Britain. Future control interventions need to focus on improving knowledge exchange, raising awareness of best practice controls to ensure that better management strategies are employed by farmers, including improved control at livestock markets to reduce the national transmission and thus focus on coordinated control interventions.

Sheep scab: comparison of spatial and temporal patterns determined by clinical diagnosis or ELISA

Background

Ovine psoroptic mange (sheep scab) is an infectious condition caused by an allergen-induced hypersensitivity response to the mite Psoroptes ovis. Infestation results in clinical disease, economic loss and welfare issues in many sheep-producing countries. The aim of this study was to compare the prevalence and spatial pattern of sheep scab on contiguous farms, using both self-reported clinical outbreak history (2012–2020) and serological testing with an enzyme-linked immunosorbent assay (2021/2022).

Methods

Farms included in the study were located in three regions of known high scab prevalence in North, Central and Southwest England. In total, 254 farms completed both a questionnaire, which provided the clinical scab history of the farm, and submitted results of serological testing with the ELISA.

Results

A scab outbreak was reported by 17.4% (± confidence interval [CI]: 4.6%; n = 48) of farms in 2020 based on clinical diagnosis; scab was diagnosed by the ELISA on 25.6% (± 5.5%; n = 65) of farms in 2021/2022. Comparison of self-reported clinical scab cases with the ELISA test results identified a group of farms (n = 52) that did not report scab in 2020, or in some cases did not report having scab over the previous 8 years (n = 20), but whose flocks were nevertheless seropositive in 2021/2022.

Conclusion

A small number of flocks, particularly those using common grazings in North England, where handling is infrequent, often comprising less susceptible sheep breeds, may have persistent scab infestations that are generally undetected by clinical inspection. The data highlight the advantages of serological testing to identify exposure to scab in flocks where clinical signs are less easily detected.

Graphical Abstract

Putting sheep scab in its place: A more relational approach

Since the reintroduction of sheep scab within the UK, its prevalence has increased despite several industry-led initiatives to control and manage the disease. Some studies have suggested that initiatives or policies should instead focus on specific places, such as geographically high-risk areas for sheep scab, which could allow for a more targeted approach. However, this risk of sheep scab has been measured in set geographical areas, without the reference to the interplay of topography, host, pathogen and the way in which humans socially and culturally define risk and place, potentially limiting the effectiveness of preventative initiatives. Therefore, the aim of the current study was to understand how place influences sheep farmers' approaches to the identification and management of the risk of sheep scab in their flocks. Qualitative data was collected from 43 semi-structured interviews with sheep farmers from England, Scotland, and Wales and was analysed by using the constant comparative approach. The codes were grouped into four concepts that influenced farmers' decision-making strategies for sheep scab control: perception of place; risk identification; risk categorisation; and risk management. These concepts were used as an analytical framework to identify three different 'places': 'uncontrollable places', 'liminal places' and 'protective places'. Each place reflects a different sheep scab control strategy used by farmers and shaped by their perceptions of place and risk. The 'uncontrollable places' category represented farmers who were located in areas that were geographically high-risk for sheep scab and who experienced a high frequency of sheep scab infestations in their flocks. The risk posed by their local landscape and neighbouring farmers, who neglected to engage in preventative behaviours, led them to feel unable to engage in effective risk management. Thus, they viewed scab as uncontrollable. The farmers within the 'liminal places' category were characterised as farmers who were located in high-risk areas for sheep scab, but experienced low levels of sheep scab infestations. These farmers characterised the risks associated with sheep scab management in terms of needing to protect their reputation and felt more responsibility for controlling sheep scab, which influenced them to engage in more protective measures. The farmers within the 'protective places' category were characterised as farming within low-risk areas and thus experienced a low level of sheep scab infestations. These farmers also described their risk in terms of their reputation and the responsibility they held for protecting others. However, they sought to rely on their low geographical risk of sheep scab as a main source of protection and therefore did not always engage in protective measures. These results suggest that place-based effects have significant impacts on sheep farmers' beliefs and behaviours and thus should be considered by policymakers when developing future strategies for sheep scab control.

Piloting an approach to scab control on Welsh sheep farms

Introduction

Sheep scab caused by Psoroptes ovis, is a disease of concern to many stakeholders in Wales due to its welfare implications. There are good diagnostic tests and treatments available to deal with the disease. Even so, it remains a problem in Welsh flocks. As such a coordinated approach is required to deal with this issue in a more sustainable manner.

Pilot design

Sheep scab positive ‘index’ farms were initially diagnosed using a skin scrape to identify P. ovis mites. Contiguous farms were identified and antibody responses used to confirm onward infestation. All infested farms were treated by either dipping with an organophosphate (OP) dip or injecting with a licensed macrocyclic lactone (ML) product depending on farmer choice.

Results

Three positive ‘index’ farms were identified along with 12 contiguous properties. Positive serological responses were observed in seven of the 12 contiguous farms; four of which were treated by OP dip and three by an injectable ML product.

Discussion

To avoid reinfestation of treated farms, dealing with disease on contiguous properties is crucial. Through the project coordinating team, three local outbreaks of scab were dealt with in a short space of time with appropriate diagnosis and treatment being carried out. Some farmers were uncooperative and strategies such as providing additional external support and veterinary involvement might alleviate these issues in the future. This coordinated approach is recommended to veterinary surgeons in the field when dealing with scab on farm.

Entomopathogenic Fungi and Bacteria in a Veterinary Perspective

Simple Summary

Several fungal species are well suited to control arthropods, being able to cause epizootic infection among them and most of them infect their host by direct penetration through the arthropod’s tegument. Most of organisms are related to the biological control of crop pests, but, more recently, have been applied to combat some livestock ectoparasites. Among the entomopathogenic bacteria, Bacillus thuringiensis, innocuous for humans, animals, and plants and isolated from different environments, showed the most relevant activity against arthropods. Its entomopathogenic property is related to the production of highly biodegradable proteins. Entomopathogenic fungi and bacteria are usually employed against agricultural pests, and some studies have focused on their use to control animal arthropods. However, risks of infections in animals and humans are possible; thus, further studies about their activity are necessary.

Abstract

The present study aimed to review the papers dealing with the biological activity of fungi and bacteria against some mites and ticks of veterinary interest. In particular, the attention was turned to the research regarding acarid species, Dermanyssus gallinae and Psoroptes sp., which are the cause of severe threat in farm animals and, regarding ticks, also pets. Their impact on animal and human health has been stressed, examining the weaknesses and strengths of conventional treatments. Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae are the most widely employed agents. Their activities have been reviewed, considering the feasibility of an in-field application and the effectiveness of the administration alone or combined with conventional and alternative drugs is reported.

Gastrointestinal nematode control practices in ewes: Identification of factors associated with application of control methods known to influence anthelmintic resistance development

Gastrointestinal nematodes (GIN) negatively impact productivity and welfare in sheep globally and are estimated to cost the European sheep industry €157-477 million annually. GIN are mainly controlled by anthelmintic treatment, however, as anthelmintic resistance becomes prominent, the routine treatment of ewes against GIN has been questioned. A questionnaire survey of 383 sheep farmers in Great Britain was conducted to identify strategies currently used to control GIN infections in ewes. Ordinal and binary regression analysis were used to identify factors associated with use of practices known to influence anthelmintic resistance development, including number and timing of ewe GIN anthelmintic treatment, targeted selective treatment (TST) of ewes, drench and move of ewes and long-acting moxidectin treatment of periparturient ewes. Participating farmers treated their ewes against GIN 1.68 times per year on average, with 42.3% and 32.1% of participating farmers worming their ewes once or twice a year on average, respectively. 17.2% of participating farmers wormed their ewes more than twice a year, and 8.4% never worm their ewes. Participating farmers who devised GIN control strategies based on SCOPS guidelines treated their ewes significantly less per year (P < 0.001), whilst those determining treatment timing based on ewe DAG scores or the time of year treated their ewes significantly more frequently (P < 0.001). Farmers who devised GIN control strategies in conjunction with their vet had greater odds of using TST (P < 0.001), as well as farmers who determined flock treatment timing based on ewe condition (P = 0.027). The use of narrow spectrum flukicides was significantly associated with reduced number of annual ewe GIN anthelmintic treatments (P < 0.001), TST of ewes against GIN (P < 0.001) and the avoidance of moving ewes to clean pastures following GIN treatment (P < 0.001). The presence of sheep scab on a farm or in the area was significantly associated with increased annual GIN treatments for ewes (P = 0.002), not using TST strategies to control GIN in ewes (P < 0.001) and moving ewes to clean pasture after anthelmintic treatment, whilst using macrocyclic lactones treatments to prevent sheep scab was significantly associated with the treatment of periparturient ewes with long-acting moxidectin (P = 0.001). This research suggests that by encouraging the application of evidence based targeted or targeted selective treatment strategies, further interaction between farmers and veterinarians/SCOPS guidance, and the uptake of best practices for controlling liver fluke and sheep scab on farms, sustainable GIN control strategies can become the common practice in ewes.

Molecular characterization of four novel serpins in Psoroptes ovis var. cuniculi and their implications in the host-parasite interaction

Psoroptes ovis var. cuniculi infestation rapidly causes skin lesion, cutaneous inflammatory and subsequent adaptive immune response in rabbits. To success feeding and survive on the host skin, this mite should product bioactive molecules to confront host tissue repair and immune defense, but these molecules of this mite remains mostly unknown. Serpins have been proved to involve in diverse biological functions including parasite reproduction, survival and modulating host defense. Limited information is currently available on serpins from Psoroptes mites. Herein, we identified four novel serpins (PsoSP3-PsoSP6) in P. ovis var. cuniculi using bioinformatics and molecular biology techniques. Sequence analysis revealed that PsoSP3-PsoSP6 comprised the common features of typical serpins superfamily including serpin domains, signature or the reactive centre loop (RCL) domain. The recombinant PsoSP4-PsoSP6 (rPsoSP4-rPsoSP6) revealed variable potency inhibition on trypsin, chymotrypsin and elastase except for rPsoSP3 in inhibitory activity assays. By quantitative RT-PCR, the expressions of PsoSP3 and PsoSP4 were higher in juvenile mites (larva and nymph) than in adult mites, however, PsoSP5 and PsoSP6 appeared near-exclusive expression in adult female mites. Immunolocalization showed that native PsoSP4 protein was localized in uterus, whilst native PsoSP3, PsoSP5 and PsoSP6 were specifically localized in the ovarian nutritive cell (ONC) in ovary. Our findings indicated that PsoSP3-PsoSP6 might play critical roles in development and reproduction physiologies. rPsoSP4-rPsoSP6 might participate in modulating host inflammation, immune response and tissue repair.

Traceback of the Psoroptes outbreak in British Columbian bighorn sheep (Ovis Canadensis)

Psoroptes are a non-burrowing, ectoparasitic, mange-causing mite that has been documented in American bighorn sheep populations throughout the 19th and 20th centuries; however, it was not seen on Canadian bighorn sheep until 2006. The aim of this study was to determine the potential source of the Psoroptes outbreak in Canadian bighorn sheep. Morphological and molecular analyses were used to compare mites recovered from outbreak-associated bighorn sheep, pet rabbits in Canada, and on historically infested bighorn sheep in the USA. The results revealed that Psoroptes acquired from the Canadian and outbreak-associated American bighorn sheep were morphologically more similar to those collected from rabbits than mites on historically infested bighorn sheep. Outer opisthosomal setae lengths measured an average of 81.7 μm (±7.7 μm) in outbreak associated bighorn mites, 88.9 μm (±12.0 μm) in rabbit mites and 151.2 μm (±16.6 μm) in historically infested bighorn mites. The opisthosomal lobe morphology of bighorn mites in the outbreak herds was also more similar to that of rabbit mites, previously described as P. cuniculi, than historically infested bighorn mites, which match previous descriptions of P. ovis. This finding was supported by DNA sequence data of the mitochondrial cytochrome B gene. This is the first report of Psoroptes of the rabbit ecotype on bighorn sheep. The morphological and molecular data therefore support the hypothesis that the source of Psoroptes outbreak in Canadian bighorn sheep represented a disease spillover event from rabbits rather than transmission from infested American bighorn sheep populations.

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Psoroptes infestations are not host specific.

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Canadian bighorn Psoroptes are morphologically distinct from USA bighorn Psoroptes.

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Mitochondrial DNA gene CytB can be used to differentiate Psoroptes strains.

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The Canadian bighorn sheep Psoroptes outbreak likely came from rabbits not USA bighorns.

Dermal immune responses against Psoroptes ovis in two cattle breeds and effects of anti-inflammatory dexamethasone treatment on the development of psoroptic mange

Psoroptic mange is a common disease of livestock, caused by Psoroptes ovis. Compared to Holstein–Friesian (HF) cattle, the Belgian Blue (BB) cattle breed is highly susceptible to the infestation. However, the mechanism for this difference is still unclear. To determine the factors responsible for this breed susceptibility, the immune response to P. ovis was studied in experimentally infested BB and HF cattle, using clinical signs, histology, immunohistochemical profiling and gene expression analysis of skin biopsies. The mite numbers and lesion area of BB cattle were greater than in HF during the whole study period. Significant influxes of eosinophils in the epidermis and dermis were detected in comparison with the pre-infestation samples in both breeds, with significantly higher eosinophils in BB at 6 weeks post infestation (wpi). Mast cell numbers were unaffected at all stages of infestation in HF, but were significantly elevated relative to pre-infestation in BB cattle at 2 and 6 wpi. The more pronounced cutaneous eosinophilia and higher IL-4 levels at 6 wpi in BB cattle suggest that a Th2-type immune response is underlying the higher susceptibility of the BB breed. In naturally infested BB cattle, development of the psoroptic mange lesions and eosinophils and CD3+ T cell areas were severely depressed after anti-inflammatory treatment with dexamethasone. Together, these results suggest that a stronger Th2-type immune response to P. ovis causes the skin lesions in psoroptic mange in BB cattle and that local anti-inflammatory treatment could potentially be an alternative to control the pathology caused by this parasite.

Molecular characterization and serodiagnostic potential of two serpin proteins in Psoroptes ovis var. cuniculi

BACKGROUND

Psoroptes ovis var. cuniculi is a common ectoparasite of wild and domestic rabbits worldwide that causes economically devastating losses in commercial rabbit husbandry and significantly affects the overall health of rabbits. Serine proteinase inhibitor (serpin) is present in almost all organisms that are involved in host-pathogen interactions, inflammatory responses, and reproductive development, among others. However, very little research has been carried out on P. ovis var. cuniculi serpins.

METHODS

Two serpin genes of P. ovis var. cuniculi (Pso c 27 and PsoSP2 cDNAs) were cloned and molecularly characterized. The transcriptional profiles and tissue localization of these two serpins in P. ovis var. cuniculi were investigated by quantitative real-time PCR and immunohistochemistry, respectively. The potential function of recombinant Pso c 27 and PsoSP2 (rPso c 27 and rPsoSP2) in the serodiagnosis of P. ovis var. cuniculi infestation in rabbits was evaluated using a newly devleoped indirect enzyme-linked immunosorbent assay.

RESULTS

Both the 523-residue Pso c 27 and the 240-residue PsoSP2 proteins contained typical serpin domains and signatures. Both Pso c 27and PsoSP2 cDNAs were expressed throughout the life-cycle; specifically, the cDNAs showed significantly higher expression in female mites than in larva, nymph, and male mites (Pso c 27: F(3, 8) = 1935.953, P < 0.0001; PsoSP2: F(3, 8) = 660.669, P < 0.0001). The native Pso c 27 and PsoSP2 proteins localized in the ovary and mouthparts of adult female mites, respectively. Compared to rPsoSP2, rPso c 27 showed better diagnostic efficiency, with higher values of sensitivity, specificity, and area under the receiver operating characteristic curve (rPso c 27 vs rPsoSP2: 96.0 vs 90.0%; 90.91 vs 78.18%; 0.988 vs 0.964, respectively). Moreover, rPso c 27 showed seropositivity in 80% of the rabbits as early as the 2 weeks post-infestation, prior to visible clinical signs and microscopy-positive of skin scrapings.

CONCLUSIONS

These results suggest that these two serpins may play essential roles in reproductive development, serum-feeding, and pathogenicity of P. ovis var. cuniculi. Compared to PsoSP2, Pso c 27 appears to be a potential antigen for serodiagnosis of P. ovis var. cuniculi infestation in rabbits, especially at the early stage of infestation.

New insights into the use of a mite count reduction test for the detection of therapeutic acaricide efficacy in Psoroptes ovis in cattle

When used for the evaluation of drug efficacy against Psoroptes ovis, the diagnostic performance of different sampling strategies for a mite count reduction test (MCRT) remains unclear. In the present study, a novel simulation framework was constructed that accounted for relevant biological features of P. ovis infestations in cattle and that was parameterized with field data from 16 farms (154 animals). Second, this framework was applied to explore the impact of study specific factors (number of animals, number of sampled lesions, and number of scrapings per lesion) and biological factors (mite infestation intensity and size of lesions) on the diagnostic performance of MCRT. Its outcome provided a basis to determine the diagnostic performance of MCRT when it was applied according to the World Association for the Advancement in Veterinary Parasitology (WAAVP) and the European Medicine Agency (EMA) guidelines, and to formulate recommendations to ensure a good diagnostic performance of the MCRT. For both guidelines, the MCRT allowed to correctly detect (power 80%) reduced and normal efficacy when the therapeutic efficacy was <70%, and ≥95%, respectively. The results highlighted a reliable diagnostic performance of the MCRT when performed as recommended by WAAVP and EMA for the detection of normal drug efficacy. When used for the detection of reduced efficacy, therapeutic efficacies between 70% and 90% could not be detected with sufficient reliability. The diagnostic performance can be improved by increasing the total number of skin scrapings (increasing the number of animals, number of sampled lesions and/or number of samples per lesion). In order to help researchers and veterinarians to optimize the design of the MCRT to their field settings, the findings were translated into a simple tool.

Psoroptes ovis-Early Immunoreactive Protein (Pso-EIP-1) a novel diagnostic antigen for sheep scab

AIMS

Serodiagnosis of sheep scab is an established diagnostic method and has become popular in recent years. However, the current diagnostic antigen, Pso o 2, has shown promise as a component of a recombinant vaccine for scab, making it incompatible with discriminating between infected and vaccinated animals (DIVA). Here, we describe the discovery and characterization of a novel Psoroptes ovis immunodiagnostic antigen, P. ovis-Early Immunoreactive Protein-1 (Pso-EIP-1).

METHODS AND RESULTS

Pso-EIP-1 is a highly abundant member of a six-gene family with no known homologs, indicating its potential uniqueness to P. ovis. Expression of recombinant Pso-EIP-1 (rPso-EIP-1) required a C-terminal fusion protein for stability and specific IgG immunoreactivity against rPso-EIP-1 was observed in sheep serum from 1 to 2 weeks post-infestation, indicating its highly immunogenic nature. Two of the three in silico-predicted B-cell epitopes of Pso-EIP-1 were confirmed by in vitro epitope mapping and, in a direct comparison by ELISA, Pso-EIP-1 performed to the same levels as Pso o 2 in terms of sensitivity, specificity and ability to diagnose P. ovis on sheep within 2 weeks of infestation.

CONCLUSION

Pso-EIP-1 represents a novel diagnostic antigen for sheep scab with comparable levels of sensitivity and specificity to the existing Pso o 2 antigen.

Temporal analysis of the bovine lymph node transcriptome during cattle tick (Rhipicephalus microplus) infestation

Livestock production is a fundamental source of revenue and nutrition, wherein cattle-farming constitutes one of the major agricultural industries. Vectors and vector-borne diseases constitute one of the major factors that decrease the livelihood of all farming communities, more so in resource-poor communities and developing countries. Understanding the immunological responses during tick infestation in cattle is instrumental in the development of novel and improved tick control strategies, such as vaccines. In this study, gene expression patterns were compared within the lymph nodes of three cattle breeds at different life stages of the cattle tick, Rhipicephalus microplus. For Bonsmara (5/8Bos taurus indicus × 3/8B. t. taurus) cattle specifically, some 183 genes were found to be differentially expressed within the lymph nodes during larval and adult tick feeding, relative to uninfested cattle. Overall, the data provides evidence for a transcriptional regulatory network that is activated during immature tick infestation, but is down-regulated towards basal transcriptional levels when adult ticks are feeding. Specific processes in the lymph nodes of Bonsmara cattle were found to be differentially regulated on a transcriptional level. These include: (1) Leukocyte recruitment to the lymph node via chemokines and chemotaxis, (2) Trans-endothelial and intranodal movement on the reticular network, (3) Active regulation of cellular transcription and translation in the lymph node (including leukocyte associated cellular regulatory networks) and (4) Chemokine receptors regulating the movement of cells out of the lymph node. This work provides a first transcriptome analysis of bovine lymph node responses in tick-infested cattle. Findings show a dynamic immune response to tick infestation for the Bonsmara cattle breed, and that suppression of the maturation of the cattle hosts' immunity is especially evident during the larval feeding stages.

Resistance against macrocyclic lactones in Psoroptes ovis in cattle

Background

Psoroptic mange is an important disease in Belgian Blue cattle. Treatment failure of macrocyclic lactones against Psoroptes ovis has been reported, but clear evidence of in vivo resistance is lacking. This study assessed the efficacy of macrocyclic lactone products on 16 beef farms in Belgium and the Netherlands in vivo and in vitro.

Methods

On each farm a group of animals (n = 7–14) with psoroptic mange was treated with two subcutaneous injections of a macrocyclic lactone product with 7–10 days interval (15 farms) or a single injection with a long-acting macrocyclic lactone (1 farm). In vivo efficacy was assessed by the reduction in mite counts, clinical index (proportion of the body surface affected by lesions), the proportion of the animals with negative mite counts after the first treatment round and the number of treatment rounds needed to obtain zero mites counts in all animals. A mite population was categorized as sensitive when the mite count reduction after the first treatment round > 95% and the lower limit of the uncertainty interval > 90%. Resistance was detected when both parameters were below their threshold and suspected when one parameter was too low. In vitro knockdown and mortality were evaluated in a contact test.

Results

The proportion of the animals with negative mite counts after the first treatment round varied from 0 to 80%. All farms needed two or more treatments rounds to obtain zero mite counts on all animals. Clinical index only started to reduce after the second treatment round. Mite populations from three farms were categorized as sensitive, one as suspected resistant and 12 as resistant. No correlation was found between in vitro lethal dose 50 and knockdown dose 50 values and in vivo efficacy parameters.

Conclusions

Unambiguous treatment failure was detected on 12 out of 16 farms, confirming the presence of macrocyclic lactone resistance on Belgian Blue beef farms. In vitro parameters could not discriminate the farms based on their in vivo sensitivity. The mean reduction in mite counts and the lower limit of the confidence interval are proposed as parameters to identify acaricide resistance.

A genomic analysis and transcriptomic atlas of gene expression in Psoroptes ovis reveals feeding- and stage-specific patterns of allergen expression

Background

Psoroptic mange, caused by infestation with the ectoparasitic mite, Psoroptes ovis, is highly contagious, resulting in intense pruritus and represents a major welfare and economic concern for the livestock industry Worldwide. Control relies on injectable endectocides and organophosphate dips, but concerns over residues, environmental contamination, and the development of resistance threaten the sustainability of this approach, highlighting interest in alternative control methods. However, development of vaccines and identification of chemotherapeutic targets is hampered by the lack of P. ovis transcriptomic and genomic resources.

Results

Building on the recent publication of the P. ovis draft genome, here we present a genomic analysis and transcriptomic atlas of gene expression in P. ovis revealing feeding- and stage-specific patterns of gene expression, including novel multigene families and allergens. Network-based clustering revealed 14 gene clusters demonstrating either single- or multi-stage specific gene expression patterns, with 3075 female-specific, 890 male-specific and 112, 217 and 526 transcripts showing larval, protonymph and tritonymph specific-expression, respectively. Detailed analysis of P. ovis allergens revealed stage-specific patterns of allergen gene expression, many of which were also enriched in “fed” mites and tritonymphs, highlighting an important feeding-related allergenicity in this developmental stage. Pair-wise analysis of differential expression between life-cycle stages identified patterns of sex-biased gene expression and also identified novel P. ovis multigene families including known allergens and novel genes with high levels of stage-specific expression.

Conclusions

The genomic and transcriptomic atlas described here represents a unique resource for the acarid-research community, whilst the OrcAE platform makes this freely available, facilitating further community-led curation of the draft P. ovis genome.

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.

Performance of the Psoroptes ovis antibody enzyme-linked immunosorbent assay in the face of low-level mite infestation

Psoroptes ovis mites, the causative agent of sheep scab, can severely compromise sheep welfare and production. However, in subclinical infections, mite detection is difficult increasing the risk of spread. A recent serodiagnostic test, based on detecting host antibodies to the P ovis allergen, Pso o 2, has made the detection of subclinical infection possible. The use of this test was demonstrated in subclinical situations, through an opportunistic observational study on an extensive hill farm and a lowland flock with recently introduced, quarantined livestock. Twelve animals were tested from each group. Breeding ewes and lambs on the hill farm had seroprevalences of 16 per cent (12.5-17.8 per cent) and 8.3 per cent (4.8-10.1 per cent), respectively. Quarantined store lambs had a seroprevalence of 16.7 per cent (13.2-18.5 per cent); no evidence of P ovis was found in quarantined replacement ewes. By detecting subclinical infection, this serological test could be a powerful tool in sheep scab control, for quarantine procedures, accreditation programmes, and possibly regional or national eradication protocols.

The prevalence and distribution of sheep scab in Wales: a farmer questionnaire survey

Outbreaks of ovine psoroptic mange in the U.K. have increased 100-fold since its deregulation in 1992, with the highest prevalence in Wales, a region of high sheep density. A cross-sectional, retrospective, questionnaire-based survey of 7500 members of the association of Welsh lamb and beef farmers [Welsh Lamb and Beef Producers Ltd (WLBP)] was used to investigate the prevalence and distribution of sheep scab in this region in 2015. The survey was completed by 14.0% (n = 972) of potential respondents. Scab outbreaks were reported on 15.8% (n = 154) of farms in 2015. However, 29.0% (n = 282) of farms reported at least one scab outbreak and 2.4% (n = 23) of farms had experienced between six and 10 outbreaks in the previous 10 years. Most outbreaks occurred during September-January (83.0%, n = 150), and were clustered around Brecon (mid-Wales) and Bangor (North Wales). Farmers who used common grazing were significantly more likely to report scab outbreaks in the previous 10 years than farmers who did not. No quarantine procedures for sheep bought in were used by 29.0% (n = 262) of farmers. Future research should be directed towards the development of localized management programmes, with a particular focus on areas of common grazing.

Evaluation of Oxidative Stress in Sheep Infected with Psoroptes Ovis using Total Antioxidant Capacity, Total Oxidant Status, and Malondialdehyde Level

Introduction

The study aimed at evaluating oxidative stress using malondialdehyde (MDA), total antioxidant capacity (TAC), total oxidant status (TOS), and oxidative stress index (OSI) markers in sheep naturally infected with Psoroptes ovis(Acari).

Material and Methods

The study was performed on 40 sheep divided into two equal groups: a healthy group (group I) and a group naturally infected with Psoroptes ovis (group II). The sera were obtained by centrifuging blood samples collected from the vena jugularis and serum MDA level changes in the samples were measured spectrophotometrically. Commercially available test kits were used for the measurement of TAC and TOS levels. The percentage ratio of TOS level to TAC level was accepted as OSI.

Results

The serum malondialdehyde, total oxidant status levels, and oxidative stress index increased significantly (P < 0.01) in group II, while the serum total antioxidant capacity levels decreased significantly (P < 0.01) in this group. Negative correlations between total antioxidant capacity and total oxidant status and total antioxidant capacity and malondialdehyde, and a positive correlation between total oxidant status and malondialdehyde were found in infected sheep.

Conclusion

The obtained results indicated the relationship between oxidant/antioxidant imbalance and Psoroptes ovis infection in sheep. Their MDA, TAC, TOS, and OSI markers may be used to determine the oxidative stress in natural infections with Psoroptes ovis.

Preliminary analysis of Psoroptes ovis transcriptome in different developmental stages

Background

Psoroptic mange is a chronic, refractory, contagious and infectious disease mainly caused by the mange mite Psoroptes ovis, which can infect horses, sheep, buffaloes, rabbits, other domestic animals, deer, wild camels, foxes, minks, lemurs, alpacas, elks and other wild animals. Features of the disease include intense pruritus and dermatitis, depilation and hyperkeratosis, which ultimately result in emaciation or death caused by secondary bacterial infections. The infestation is usually transmitted by close contact between animals. Psoroptic mange is widespread in the world. In this paper, the transcriptome of P. ovis is described following sequencing and analysis of transcripts from samples of larvae (i.e. the Pso_L group) and nymphs and adults (i.e. the Pso_N_A group). The study describes differentially expressed genes (DEGs) and genes encoding allergens, which help understanding the biology of P. ovis and lay foundations for the development of vaccine antigens and drug target screening.

Methods

The transcriptome of P. ovis was assembled and analyzed using bioinformatic tools. The unigenes of P. ovis from each developmental stage and the unigenes differentially between developmental stages were compared with allergen protein sequences contained in the allergen database website to predict potential allergens.

Results

We identified 38,836 unigenes, whose mean length was 825 bp. On the basis of sequence similarity with seven databases, a total of 17,366 unigenes were annotated. A total of 1,316 DEGs were identified, including 496 upregulated and 820 downregulated in the Pso_L group compared with the Pso_N_A group. We predicted 205 allergens genes in the two developmental stages similar to genes from other mites and ticks, of these, 14 were among the upregulated DEGs and 26 among the downregulated DEGs.

Conclusion

This study provides a reference transcriptome of P. ovis in absence of a reference genome. The analysis of DEGs and putative allergen genes may lay the foundation for studies of functional genomics, immunity and gene expression profiles of this parasitic mite species.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1856-z) contains supplementary material, which is available to authorized users.

A recombinant subunit vaccine for the control of ovine psoroptic mange (sheep scab)

Sheep scab, caused by infestation with the mite Psoroptes ovis, is highly contagious, causing intense pruritus and represents a major welfare and economic concern. Disease control strategies rely upon chemotherapy, however, sustainability is questionable due to issues of chemical residues, eco-toxicity and acaricide resistance. Control by vaccination is supported by demonstration of protective immunity in sheep previously infested with P. ovis. We identified vaccine candidates for P. ovis based on: (1) antigens selected by their interaction with host signalling pathways and the host immune-response; and (2) those shown to be either immunogenic or involved in mite feeding. This resulted in the development and validation, in repeated immunisation and challenge trials, of a seven recombinant protein sub-unit cocktail vaccine. Sheep were inoculated on three occasions, 2 weeks apart, along with QuilA adjuvant. Vaccination resulted in highly significant reductions in both lesion size (up to 63%) and mite numbers (up to 56%) following challenge. Mean lesion size in vaccinates was significantly smaller than controls from 1 week post infestation (wpi) until the end of the experiment at 6 wpi. All antigens elicited serum IgG responses following immunisation and prior to infestation, whereas controls did not produce antigen-specific IgG during the pre-infestation period. Vaccinated animals showed an amnestic response, with levels of antigen-specific IgG against muGST, Pso o 1 and Pso o 2 increasing following infestation. This vaccine represents the greatest reduction in lesion size to date with a sheep scab vaccine, providing encouragement for future production of a commercially-viable means of immunoprophylaxis.

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.

Morphologic and Genotypic Characterization of Psoroptes Mites from Water Buffaloes in Egypt

Species delimitation of Psoroptes spp. and identity of the parasite in water buffaloes remain poorly defined. In this study, Psoroptes infestation on three water buffalo farms in Egypt was examined based on morphometric characteristics, especially the opisthosomal setae of adult male mites. Clinical investigations showed that 28% (196/700) of the sampled animals had mange infestation. Microscopic examinations of 80 skin scrapings indicated the occurrence of Psoroptes mites in 17 (21.3%) samples, Sarcoptes mites in 27 (33.7%) samples, and the concurrence of both in 36 (45.0%) samples. Morphologically, the Psoroptes parasite was identified as Psoroptes natalensis. DNA sequence analysis of the second internal transcribed spacer (ITS2) in 11 representative samples confirmed the diagnosis and suggested the presence of a distinct variety of Psoroptes natalensis in Egypt.

Parasitic mites of medical and veterinary importance--is there a common research agenda?

There are an estimated 0.5-1 million mite species on earth. Among the many mites that are known to affect humans and animals, only a subset are parasitic but these can cause significant disease. We aim here to provide an overview of the most recent work in this field in order to identify common biological features of these parasites and to inform common strategies for future research. There is a critical need for diagnostic tools to allow for better surveillance and for drugs tailored specifically to the respective parasites. Multi-'omics' approaches represent a logical and timely strategy to identify the appropriate mite molecules. Recent advances in sequencing technology enable us to generate de novo genome sequence data, even from limited DNA resources. Consequently, the field of mite genomics has recently emerged and will now rapidly expand, which is a particular advantage for parasitic mites that cannot be cultured in vitro. Investigations of the microbiota associated with mites will elucidate the link between parasites and pathogens, and define the role of the mite in transmission and pathogenesis. The databases generated will provide the crucial knowledge essential to design novel diagnostic tools, control measures, prophylaxes, drugs and immunotherapies against the mites and associated secondary infections.

Two major ruminant acute phase proteins, haptoglobin and serum amyloid A, as serum biomarkers during active sheep scab infestation

Two ruminant acute phase proteins (APPs), haptoglobin (Hp) and serum amyloid A (SAA), were evaluated as serum biomarkers (BMs) for sheep scab-a highly contagious ectoparasitic disease caused by the mite Psoroptes ovis, which is a major welfare and production threat worldwide. The levels of both APPs increased in serum following experimental infestation of sheep with P. ovis, becoming statistically significantly elevated from pre-infestation levels at 4 weeks post-infestation. Following successful treatment of infested sheep with an endectocide, Hp and SAA serum levels declined rapidly, with half lives of less than 3 days. In contrast, serum IgG levels which specifically bound the P. ovis-derived diagnostic antigen Pso o 2 had a half-life of 56 days. Taking into account pre-infestation serum levels, rapidity of response to infestation and test sensitivity at the estimated optimum cut-off values, SAA was the more discriminatory marker. These studies illustrated the potential of SAA and Hp to indicate current sheep scab infestation status and to augment the existing Pso o 2 serological assay to give disease-specific indications of both infestation and successful treatment.

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.

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

Background

Sheep 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.

Methods

Herein 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.

Results

Sequences 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.

Conclusion

The 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.

Veterinary Pesticides

Veterinary pesticides are used to treat a range of parasitic conditions in companion and farm animals. These products are based on a number of different compounds with different modes of action and different spectra of toxicity. The older agents include the synthetic pyrethroids and organophosphorus compounds, while the newer examples include, for example, representatives of the insect growth promoters, the neonicotinoids, and the oxadiazones. For many of these compounds, toxicity is associated with their pharmacological activity or mode of action. Thus the synthetic pyrethroids and the organophosphorus compounds exert neurotoxic effects. For others, toxicity may be associated with mechanisms that are independent of their mode of action. When used according to the manufacturer's instructions, these products are generally safe and efficacious. However, accidental contamination and misuse can lead to toxicity in operators and treated animals. These compounds are important in the treatment of parasitic disease in animals and their regulation and uses are based on favourable risk-benefit outcomes.

The use of a Psoroptes ovis serodiagnostic test for the analysis of a natural outbreak of sheep scab

BACKGROUND

Sheep scab is a highly contagious disease of sheep caused by the ectoparasitic mite Psoroptes ovis. The disease is endemic in the UK and has significant economic impact through its effects on performance and welfare. Diagnosis of sheep scab is achieved through observation of clinical signs e.g. itching, pruritis and wool loss and ultimately through the detection of mites in skin scrapings. Early stages of infestation are often difficult to diagnose and sub-clinical animals can be a major factor in disease spread. The development of a diagnostic assay would enable farmers and veterinarians to detect disease at an early stage, reducing the risk of developing clinical disease and limiting spread.

METHODS

Serum samples were obtained from an outbreak of sheep scab within an experimental flock (n = 480 (3 samples each from 160 sheep)) allowing the assessment, by ELISA of sheep scab specific antibody prior to infestation, mid-outbreak (combined with clinical assessment) and post-treatment.

RESULTS

Analysis of pre-infestation samples demonstrated low levels of potential false positives (3.8%). Of the 27 animals with clinical or behavioural signs of disease 25 tested positive at the mid-outbreak sampling period, however, the remaining 2 sheep tested positive at the subsequent sampling period. Clinical assessment revealed the absence of clinical or behavioural signs of disease in 132 sheep, whilst analysis of mid-outbreak samples showed that 105 of these clinically negative animals were serologically positive, representing potential sub-clinical infestations.

CONCLUSIONS

This study demonstrates that this ELISA test can effectively diagnose sheep scab in a natural outbreak of disease, and more importantly, highlights its ability to detect sub-clinically infested animals. This ELISA, employing a single recombinant antigen, represents a major step forward in the diagnosis of sheep scab and may prove to be critical in any future control program.

Quantitative PCR-based genome size estimation of the astigmatid mites Sarcoptes scabiei, Psoroptes ovis and Dermatophagoides pteronyssinus

Background

The lack of genomic data available for mites limits our understanding of their biology. Evolving high-throughput sequencing technologies promise to deliver rapid advances in this area, however, estimates of genome size are initially required to ensure sufficient coverage.

Methods

Quantitative real-time PCR was used to estimate the genome sizes of the burrowing ectoparasitic mite Sarcoptes scabiei, the non-burrowing ectoparasitic mite Psoroptes ovis, and the free-living house dust mite Dermatophagoides pteronyssinus. Additionally, the chromosome number of S. scabiei was determined by chromosomal spreads of embryonic cells derived from single eggs.

Results

S. scabiei cells were shown to contain 17 or 18 small (< 2 μM) chromosomes, suggesting an XO sex-determination mechanism. The average estimated genome sizes of S. scabiei and P. ovis were 96 (± 7) Mb and 86 (± 2) Mb respectively, among the smallest arthropod genomes reported to date. The D. pteronyssinus genome was estimated to be larger than its parasitic counterparts, at 151 Mb in female mites and 218 Mb in male mites.

Conclusions

This data provides a starting point for understanding the genetic organisation and evolution of these astigmatid mites, informing future sequencing projects. A comparitive genomic approach including these three closely related mites is likely to reveal key insights on mite biology, parasitic adaptations and immune evasion.

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.

Host transcription factors in the immediate pro-inflammatory response to the parasitic mite Psoroptes ovis

Background

Sheep scab, caused by infestation with the ectoparasitic mite Psoroptes ovis, results in the rapid development of cutaneous inflammation and leads to the crusted skin lesions characteristic of the disease. We described previously the global host transcriptional response to infestation with P. ovis, elucidating elements of the inflammatory processes which lead to the development of a rapid and profound immune response. However, the mechanisms by which this response is instigated remain unclear. To identify novel methods of intervention a better understanding of the early events involved in triggering the immune response is essential. The objective of this study was to gain a clearer understanding of the mechanisms and signaling pathways involved in the instigation of the immediate pro-inflammatory response.

Results

Through a combination of transcription factor binding site enrichment and pathway analysis we identified key roles for a number of transcription factors in the instigation of cutaneous inflammation. In particular, defined roles were elucidated for the transcription factors NF-kB and AP-1 in the orchestration of the early pro-inflammatory response, with these factors being implicated in the activation of a suite of inflammatory mediators.

Conclusions

Interrogation of the host temporal response to P. ovis infestation has enabled the further identification of the mechanisms underlying the development of the immediate host pro-inflammatory response. This response involves key regulatory roles for the transcription factors NF-kB and AP-1. Pathway analysis demonstrated that the activation of these transcription factors may be triggered following a host LPS-type response, potentially involving TLR4-signalling and also lead to the intriguing possibility that this could be triggered by a P. ovis allergen.

Generation, analysis and functional annotation of expressed sequence tags from the ectoparasitic mite Psoroptes ovis

Background

Sheep scab is caused by Psoroptes ovis and is arguably the most important ectoparasitic disease affecting sheep in the UK. The disease is highly contagious and causes and considerable pruritis and irritation and is therefore a major welfare concern. Current methods of treatment are unsustainable and in order to elucidate novel methods of disease control a more comprehensive understanding of the parasite is required. To date, no full genomic DNA sequence or large scale transcript datasets are available and prior to this study only 484 P. ovis expressed sequence tags (ESTs) were accessible in public databases.

Results

In order to further expand upon the transcriptomic coverage of P. ovis thus facilitating novel insights into the mite biology we undertook a larger scale EST approach, incorporating newly generated and previously described P. ovis transcript data and representing the largest collection of P. ovis ESTs to date. We sequenced 1,574 ESTs and assembled these along with 484 previously generated P. ovis ESTs, which resulted in the identification of 1,545 unique P. ovis sequences. BLASTX searches identified 961 ESTs with significant hits (E-value < 1E-04) and 584 novel P. ovis ESTs. Gene Ontology (GO) analysis allowed the functional annotation of 880 ESTs and included predictions of signal peptide and transmembrane domains; allowing the identification of potential P. ovis excreted/secreted factors, and mapping of metabolic pathways.

Conclusions

This dataset currently represents the largest collection of P. ovis ESTs, all of which are publicly available in the GenBank EST database (dbEST) (accession numbers FR748230 - FR749648). Functional analysis of this dataset identified important homologues, including house dust mite allergens and tick salivary factors. These findings offer new insights into the underlying biology of P. ovis, facilitating further investigations into mite biology and the identification of novel methods of intervention.

Transcriptomic analysis of the temporal host response to skin infestation with the ectoparasitic mite Psoroptes ovis

Background

Infestation of ovine skin with the ectoparasitic mite Psoroptes ovis results in a rapid cutaneous immune response, leading to the crusted skin lesions characteristic of sheep scab. Little is known regarding the mechanisms by which such a profound inflammatory response is instigated and to identify novel vaccine and drug targets a better understanding of the host-parasite relationship is essential. The main objective of this study was to perform a combined network and pathway analysis of the in vivo skin response to infestation with P. ovis to gain a clearer understanding of the mechanisms and signalling pathways involved.

Results

Infestation with P. ovis resulted in differential expression of 1,552 genes over a 24 hour time course. Clustering by peak gene expression enabled classification of genes into temporally related groupings. Network and pathway analysis of clusters identified key signalling pathways involved in the host response to infestation. The analysis implicated a number of genes with roles in allergy and inflammation, including pro-inflammatory cytokines (IL1A, IL1B, IL6, IL8 and TNF) and factors involved in immune cell activation and recruitment (SELE, SELL, SELP, ICAM1, CSF2, CSF3, CCL2 and CXCL2). The analysis also highlighted the influence of the transcription factors NF-kB and AP-1 in the early pro-inflammatory response, and demonstrated a bias towards a Th2 type immune response.

Conclusions

This study has provided novel insights into the signalling mechanisms leading to the development of a pro-inflammatory response in sheep scab, whilst providing crucial information regarding the nature of mite factors that may trigger this response. It has enabled the elucidation of the temporal patterns by which the immune system is regulated following exposure to P. ovis, providing novel insights into the mechanisms underlying lesion development. This study has improved our existing knowledge of the host response to P. ovis, including the identification of key parallels between sheep scab and other inflammatory skin disorders and the identification of potential targets for disease control.

Ectoparasites are the major causes of various types of skin lesions in small ruminants in Ethiopia

Ectoparasites are the major causes of skin lesions in animals. Clinical, skin scraping examination, and histopathological studies were conducted to identify and characterize skin lesions in small ruminants caused by ectoparasites. Mange mites, lice, sheep keds, and ticks were collected from the skin of affected animals for species identification. Skin biopsies were collected from affected part of the skin and fixed in 10% neutral buffered formalin for histopathology. Of 1,000 sheep and 600 goats examined, 815 (81.50%) sheep and 327 (54.5%) goats were infested with one or more types of ectoparasites. Sarcoptes scabiei var ovis, Demodex ovis, Psoroptes ovis, Bovicola ovis, Melophagus ovinus, and Amblyomma variegatum and other tick species were identified from sheep. S. scabiei var caprae, Demodex caprae, Linognathus stenopsis, and A. variegatum and other tick species were identified from goats. Gross skin lesions or defects observed on the skin include stained and ragged wool, loss of wool/hair, nodules, crusts, lichenification, and fissuring. Microscopic evaluation of H and E stained skin sections revealed lesions in the epidermal layer such as hyperkeratosis, acanthosis, and melanin inconsistency on the basal cells of the epidermis. Follicular keratosis, perifolliculitis, frunculosis, perivasculitis, and aggregates of inflammatory cells (of acute and chronic type) with fibrosis were experiential in the dermal layer of the skin. Most of the skin lesions caused by ectoparasites are overlapping. Thus, ectoparasites control program should be executed to reduce skin lesions as skins are the major export commodity of the country.

Identification of an abundant allergen from the sheep louse, Bovicola ovis

Infestation of sheep with the louse Bovicola ovis is common worldwide and leads to an allergic dermatitis referred to as 'scatter cockle'. IgE from an infested lamb was used in immunoaffinity chromatography to purify allergens from crude preparations of whole B. ovis and its faeces. SDS-PAGE of the affinity-purified eluates from both preparations showed a dominant band with M(r) of 28.5 kDa. Spleen cells from a mouse immunised with B. ovis faecal antigens were used to produce hybridomas which were screened by ELISA to identify those producing monoclonal antibodies (mAb) to the allergens purified by IgE immunoaffinity chromatography. Western blotting demonstrated that all of the mAbs examined recognised the 28.5 kDa allergen. The allergen, purified using immunoaffinity columns constructed with one of the specific mAbs, was shown to cause immediate and late-phase responses on intradermal skin testing in B. ovis-infested but not in naïve lambs. Levels of serum IgE specific for the purified allergen were significantly higher in infested than in naïve lambs (P < or = 0.0025). N-terminal and internal amino acid (aa) sequences obtained from the purified 28.5 kDa allergen were used to design primers to amplify a partial cDNA probe from B. ovis cDNA by PCR. The amplified probe was radiolabeled and used to screen a B. ovis cDNA library. The complete nucleotide sequence of the allergen was determined from the sequences of the positive clones from the library. The full-length cDNA encodes a 255 aa protein including a secretory leader sequence of 26 aas and a mature protein of 229 aas. The encoded protein showed strong homology to several hypothetical proteins of unknown function from diverse species and weak homology with lipid-binding proteins of Xenopus tropicalis and Galleria mellonella. This is the first allergen to be identified from a louse and it has been designated Bov o 1 in accordance with the criteria of the World Health Organization/International Union of Immunological Societies Allergen Nomenclature Subcommittee.

Ovine IgE and its role in immunological protection and disease

The importance of internal and external parasites in limiting productivity and compromising the welfare of sheep has provided the impetus for extensive research on ovine IgE with the objectives of better understanding protective immunological responses and developing novel methods of control; particularly vaccination. The molecular structures of ovine IgE and its high affinity receptor have been determined and the former information has assisted the development of monoclonal antibodies (mAb) to ovine IgE by 2 of 3 groups who have produced these reagents. The availability of these mAbs has enabled the description of IgE responses following infections with a wide variety of parasites in sheep and in an ovine model of atopic asthma. While IgE responses are consistently associated with parasitic diseases of sheep, it has not been proven that this antibody isotype is involved in protection. The foundation of present knowledge and reagents, together with new emerging technologies, should allow the role of IgE in parasitic diseases of sheep to be determined.

Gene expression profiling of ovine keratinocytes stimulated with Psoroptes ovis mite antigen--a preliminary study

Sheep scab is caused by the noninvasive mite, Psoroptes ovis, which initiates a profound pro-inflammatory skin response leading to lesion development. To investigate these early events between the skin and the parasite, primary ovine epidermal keratinocyte cultures were generated and challenged with mite derived antigens. The kinetics of the mRNA response of these cells were monitored by microarray. The results indicated that the cells responded within 1 h of challenge, with a significant increase in the pro-inflammatory cytokine IL-8. This result was confirmed by real-time RT-PCR, and showed that IL-8 up-regulation was maximal at 1 h but declined to pre-stimulation levels at 24 and 48 h. The IL-8 mRNA response to mite wash antigens containing secretory and/or excretory proteins was also investigated and compared to the response to whole mite antigen. These studies revealed that the mite wash antigen, at a challenge dose of 10 microg/mL, was markedly more potent and induced significantly higher levels of IL-8 mRNA than the same concentration of whole mite antigen. These results are discussed in relation to mite establishment and survival on the ovine host.