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

Hotspot sheep scab management: A community-based regional approach in England

BACKGROUND

Ovine psoroptic mange (sheep scab), caused by an infestation of the mite Psoroptes ovis, leads to clinical disease, economic loss and severely compromised animal welfare. Here, a community-based approach to the management of scab in three high-risk areas of England is described.

METHODS

For each of the 254 farms included in the study, an initial survey of their clinical sheep scab history was followed up by a blood test (ELISA) to detect the presence of antibodies to P. ovis. This facilitated the coordination of treatment across groups of farms in each region. Blood testing was then repeated at the end of the treatment programme.

RESULTS

On the first blood test in 2021/2022, 25.6% (±5.5%) of the flocks were positive for sheep scab. On the second test in 2022/2023, 9% (±3.94%) of the flocks tested were positive, showing a highly statistically significant reduction in prevalence overall, but with strong regional variation.

LIMITATIONS

generating an understanding of the flock-level nature of the blood test and confidence in its detection of scab where clinical signs were not apparent provided ongoing challenges.

CONCLUSIONS

The programme demonstrated that a focused community-based approach can be used to significantly reduce the prevalence of sheep scab in high-risk areas of England. The use of the blood test on all farms allowed the identification of subclinical sheep scab. The programme provides an effective model for sheep scab management on a national scale.

Assessment of knowledge, attitudes, and practices related to the prevalence of sheep scab among communal sheep farmers in Eastern Cape Province, South Africa

Background and Aim

Sheep scab is one of the most contagious diseases of sheep found in rural communities worldwide and is a major health and welfare concern for sheep farming. Information on the attitudes of communal farmers to sheep scab remains speculative in the Eastern Cape Province. This study aimed to investigate knowledge, attitudes, and practices related to the prevalence of sheep scab among communal sheep farmers in Eastern Cape Province, South Africa.

Materials and Methods

From June to August 2022, a cross-sectional survey using a semi-structured questionnaire (n = 160) was conducted in two rural communities of the Enoch Mgijima Local Municipality in Eastern Cape Province. Purpose sampling was used to obtain respondents' knowledge, attitudes, and management practices regarding sheep scabs.

Results

Among respondents, 81% were males and 19% were females. The majority of sheep farmers (59%) in both communities were aware of sheep scabs, but the majority (64%) did not receive any farming training. The majority of sheep farmers (65%) believed that sheep scab was the most serious threat to their sheep production since it increased mortality. In the past 3 years, approximately 57% of respondents reported an increase in the prevalence of sheep scab. The majority of farmers reported wool loss as the most noticeable clinical symptom (73%). More than 80% of sheep farmers do not use acaricide on a regular basis. Sixty-one percent of farmers prefer a pour-on topical application method. The frequency of annual dipping was every fortnight (40%), during summer and winter (24%). Most farmers (66%) regularly vaccinate their sheep.

Conclusion

The prevalence of sheep scab is increasing in these communities; however, a better understanding of the factors that facilitate its transmission is required to allow improved management and control of this disease. The government must involve extension officers and distribute them to disseminate information to farmers. Thus, it will be easy to translate the literature into action.

Treatment of sheep prior to movement: its contribution to an effective scab (psoroptic mange) management strategy

BACKGROUND

Ovine psoroptic mange (sheep scab) is an important disease of sheep worldwide caused by the parasitic mite, Psoroptes ovis. It has a negative impact on animal welfare and leads to significant economic losses for the sheep industry. Effective and targeted management is required to limit its transmission.

METHODS

A stochastic metapopulation model of sheep scab transmission is used to investigate the contribution of the treatment of sheep prior to movements to sales, gatherings (predominantly markets) and away grazing to the reduction of prevalence of farms with scab in Great Britain.

RESULTS

Treatment prior to movement to gatherings resulted in an 86% reduction in the overall prevalence of farms with scab and was more effective at reducing the overall prevalence of farms with scab than treatment before other categories of movements. The relative risk of farms having scab infection was inversely related to the percentage of farms which treated, but this relationship was not linear, with the biggest declines in the prevalence of farms with scab being achieved by small percentages of farms treating; a 50% relative reduction in the farm prevalence was achieved with only 15% of farms treating prior to gathering movements.

CONCLUSIONS

The results suggest that pre-movement treatment of sheep could make an important contribution to national scab control and, in practice, the approach could be more highly targeted if used in conjunction with known geographic and management risk factors for scab.

Development of the first PCR for detection of Psoroptes ovis var. cuniculi infection and its comparison to microscopic examination and serological assay in rabbits

Psoroptes mites are the common ecto-parasites of wild and domestic animals worldwide, which causes considerable economic losses in livestock industry. Microscopy is deemed to be the 'gold standard' for the diagnosis of Psoroptes mite infection but it has poor sensitivity for low mite infections and/or sub-clinical infections. To overcome these shortcomings, we screened four genes to develop a sensitive and specific PCR for the detection of Psoroptes mite infection in rabbits, and confirmed its practicability in detecting early infection and monitoring treatment outcome with traditional microscopy and serological tests. Results showed that PCR assay targeting ITS2 (ITS2-PCR) had a high specificity and sensitivity (detection limit: 40.3 pg/μL DNA) for detecting P. ovis DNA. In rabbits artificially infected with P. ovis, all three diagnostic tests showed the same detection rate from 14 days post infection (dpi) to 42 days dpi. However, these diagnostic tests behave differently at 7 dpi and after treatment: at 7 dpi, the detection rate of ITS2-PCR was higher than rPsoSP3-based iELISA and traditional microscopy (ITS2-PCR: 88.9%, rPsoSP3-iELISA: 77.7%, microscopy: 33.3%); at 7 days post treatment (dpt), positivity rates of ITS2-PCR and microscopy rapidly decreased to 0.00% and 11.1%, whereas rPsoSP3-iELISA remained 100% positive rate. Furthermore, the comprehensive comparisons of diagnostic performance and features of three diagnostic tests at 7 dpi were performed. Compared to ITS2-PCR or rPsoSP3-iELISA, microscopy had the lowest sensitivity, and the agreement between these assays was low (κ < 0.3). Field study showed that ITS2-PCR showed a higher detection rate than microscopy (19.4% and 11.1%, respectively). Our results suggested that the ITS2-PCR developed in this study provided a new laboratory tool for diagnosis of P. ovis var. cuniculi infection, and it had advantages over microscopic examination in detection low-level mite infections and serological assay in monitoring treatment outcome.

Comparative assessment of different ivermectin and doramectin formulations for mange control in grazing steers

Psoroptic mange causes relevant losses of productivity in cattle. Macrocyclic lactones are one of the main pharmacological tools recommended for controlling it. The aim of the current work was to compare the relationship between the pharmacokinetic behavior and the effectiveness of both ivermectin (IVM) and doramectin (DRM) following their administration as either the traditional (1 %) or long-acting (3.15-3.5 %) injectable formulations to cattle naturally infected with Psoroptes ovis. The overall work involved three trials (1, 2 and 3) carried out on commercial beef cattle farms (grazing systems). In Trial 1, 20 grazing steers with active mange infection were allocated into 2 groups (n = 10) and treated subcutaneously (SC) with either IVM (1 %) or DRM (1%) at 0.2 mg/kg. In Trial 2, 16 grazing steers with active mange divided in 2 groups (n = 8) were treated SC with either IVM 1 % (0.2 mg/kg) or IVM 3.15 % long-acting (0.63 mg/kg). In Trial 3, 2 groups of mange infected steers (n = 8) were treated SC with either IVM 3.15 % (0.63 mg/kg) or DRM 3.5 % (0.7 mg/kg). Blood samples were collected of each experimental group and the drug systemic availability was estimated by measuring of IVM/DRM concentrations by HPLC. Skin scraping samples were collected from each animal and mites were counted at 14, 21 and 28 days post-treatment. In Trial 1, the mite density score on day 14 was significantly lower for DRM (0.60) compared to IVM (1.80) (P = 0.019). Based on the number of animals clinically cured (negative to the presence of mites), the efficacy of DRM was higher (80 %) than that obtained for IVM (10 %) (P < 0.05). DRM systemic exposure measured as AUC was 1.37-fold higher compared to IVM. In Trial 2, even though IVM exposure was significantly greater after the long-acting (3.15 %) compared to the traditional formulation (1 %), none of the treatments significantly reduced the mite density score, with a percentage of animals cured between 0 % and 37.5 % after both IVM treatments. In Trial 3, the 100 % of cured animals were achieved at day 21 (IVM 3.15 %) and at day 28 (DRM 3.5 %) post-treatment. In conclusion, DRM treatment could offer some therapeutic advantages in field situations where IVM fails to control mange. Depending on the level of susceptibility of the mite population, long-acting pharmaceutical formulations can be useful to control Psoroptic mange in cattle. The use of macrocyclic lactones for mange control in cattle should be based on appropriate diagnosis on each individual farm.

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.

Pharmacokinetic and pharmacodynamic considerations for treating sarcoptic mange with cross-relevance to Australian wildlife

Sarcoptes scabiei is the microscopic burrowing mite responsible for sarcoptic mange, which is reported in approximately 150 mammalian species. In Australia, sarcoptic mange affects a number of native and introduced wildlife species, is particularly severe in bare-nosed wombats (Vombatus ursinus) and an emerging issue in koala and quenda. There are a variety of acaricides available for the treatment of sarcoptic mange which are generally effective in eliminating mites from humans and animals in captivity. In wild populations, effective treatment is challenging, and concerns exist regarding safety, efficacy and the potential emergence of acaricide resistance. There are risks where acaricides are used intensively or inadequately, which could adversely affect treatment success rates as well as animal welfare. While reviews on epidemiology, treatment strategies, and pathogenesis of sarcoptic mange in wildlife are available, there is currently no review evaluating the use of specific acaricides in the context of their pharmacokinetic and pharmacodynamic properties, and subsequent likelihood of emerging drug resistance, particularly for Australian wildlife. This review critically evaluates acaricides that have been utilised to treat sarcoptic mange in wildlife, including dosage forms and routes, pharmacokinetics, mode of action and efficacy. We also highlight the reports of resistance of S. scabiei to acaricides, including clinical and in vitro observations.

Persistent activity and therapeutic efficacy of Delcid® 7.5 against scab mites (<i>Psoroptes ovis</i>) in sheep

The purpose of the research is to study persistent activity and therapeutic efficacy of Delcid® 7.5 against scab mites Psoroptes ovis in sheep.

Materials and methods. The studies were performed in the Bukhty peasant farm enterprise in November 2021 on the Kizlyarsky District winter pastures in the Republic of Dagestan. Three groups of sheep were formed, of which two groups (second and third) had a confirmed clinical diagnosis of psoroptic mange (P. ovis) and one group (first) was free from scab mites. Sheep from the first and second groups were treated with Delcid at a dose of 10 ml of the drug per animal. After 10 days, sheep from the second group were treated with the drug repeatedly at the same dose. Sheep from the first and second groups were treated with the drug applied on dry and intact skin of the back along the spine using the drop method. The third control (infected) group of animals was not treated. All experimental groups of sheep were kept in a common flock. The Delcid persistent activity and thera-peutic efficacy were evaluated by clinical examination and microscopy of the skin for P. ovis mites before the experiment started and at 1, 3, 7, 10, 14, 21, 25 and 30 days after treatment in the first group and at 1, 3, 7, 11, 13, 17, 20, 24, 31, 35 and 40 days in the second and third groups of sheep.

Results and discussion. It was found that Delcid 7.5 showed persistent activity in sheep against psoroptic mange pathogens for 21 days after a single treatment at a dose of 10 ml per animal. Delcid acaricidal effect after double treatment against P. ovis was 31 days.

Moxidectin use in Scottish sheep flocks suggests a need for clearer product labelling and communication of updated SCOPS guidelines

BACKGROUND

Guidelines for sustainable use of moxidectin were established in 2020. This study aimed to identify how Scottish sheep farmers are using this key endectocide and estimate its effectiveness against gastrointestinal nematodes.

METHODS

Questionnaires were distributed to sheep farmers across Scotland, and analysis focused on moxidectin use in relation to Sustainable Control of Parasites in Sheep (SCOPS) guidelines. Farmers using moxidectin in their flock volunteered to submit post-treatment sheep faecal samples, which were analysed for the presence of gastrointestinal nematodes using faecal egg counts with polymerase chain reaction to determine species.

RESULTS

Despite 70% of farmers using moxidectin in 2020, knowledge levels varied: 24% of farmers included other anthelmintics when asked about moxidectin use. Moxidectin was used for a wide variety of reasons, and most farmers did not consistently follow SCOPS guidelines. Despite only 2 of 76 farmers reporting failure of moxidectin treatment, gastrointestinal nematodes were found following moxidectin treatment on five out of six farms tested and included Teladorsagia circumcincta, Cooperia curticei, Haemonchus contortus and Nematodirus sp.

CONCLUSION

Findings from this project indicate the need for improved anthelmintic product labelling and farmer support to encourage sustainable use. The presence of nematodes in treated animals is suggestive of anthelmintic resistance.

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.

Spatial and temporal analysis of sheep scab notifications in Scotland, 2014-2019

BACKGROUND

Sheep scab is considered an endemic disease of great welfare and economic significance in the UK.

METHOD

This paper provides an up-to-date assessment of the impact of Sheep Scab (Scotland) Order 2010 on sheep scab notifications in Scotland between 1 January 2014 and 31 December 2019, using data collected by the APHA.

RESULTS

In total, 564 sheep scab notifications were reported from 503 unique holdings, of which 44 holdings (8.7%) reported more than one incident. The number of notifications did not differ between years, with 81, 84, 93, 101, 109 and 97 notifications recorded in 2014, 2015, 2016, 2017, 2018 and 2019, respectively: representing an average annual notification prevalence of 0.63% (1/159 flocks/year). A total of 413/564 records documented how notifications were resolved, with macrocyclic lactone and organophosphate treatments accounting for 79.6% and 20.4% of resolutions, respectively.

CONCLUSION

Our results suggest that the Order has facilitated the notification of sheep scab in Scotland (including trends and preferred methods of resolution), allowed industry and government to identify previously unidentified potentially free areas as well as recurrent incidents on sheep farms, and start to understand better the geographical and temporal nature of scab outbreaks. However, concerns remain about a potential lack of engagement, evidenced by the low notification prevalence and stagnant annual notification rates.

Assessment of Avermectins-Induced Toxicity in Animals

Macrocyclic lactones, particularly the avermectins, have completely revolutionized the approaches aimed at control of parasites. These avermectins are the most widely used anti-parasitic drugs in veterinary field with sales exceeding one billion US dollars annually. However, before clinical usage, their safety evaluation in the animals is a major critical factor that must be considered. Many studies have reported the negative effects of avermectins like ivermectin, abamectin, doramectin, and eprinomectin on the host animals. These harmful effects arise from avermectins targeting GABA and glutamate-gated chloride channels present both in the parasites and the host animals. In this review, various modes of avermectins action along with the negative effects on the host like nephrotoxicity, hepatotoxicity, neurotoxicity, reproductive toxicity, and endocrine disruption were discussed in detail. Furthermore, other important issues like ecotoxicity, drug resistance, and drug residues in milk associated with avermectins usage were also discussed, which need special attention.

Drug dose and animal welfare: important considerations in the treatment of wildlife

A recent publication in Parasitology Research by (Old et al. Parasitol Res 120:1077-1090, 2021) raises the topical and often controversial issue of the treatment of wildlife by personnel with little or no formal scientific training (e.g. wildlife carers). In a valuable contribution to the subject, Old and colleagues document a wide range of topical (pour-on) application doses and frequencies of moxidectin (Cydectin®) administered in situ to bare-nosed wombats (Vombatus ursinus) by members of the wildlife carer/treater community in southeast Australia to treat sarcoptic mange disease. This treatment occurred under minor use permits issued by the Australian Pesticides and Veterinary Management Authority (APVMA). These permits do not require veterinary supervision, although carers are registered and are expected to comply with the guidelines of this permit.The prevalence and severity of sarcoptic mange in wildlife is influenced by a variety of factors including mite biology, environmental conditions, population density, animal behaviour and immune susceptibility (Browne et al. Bioscience, 2021). In bare-nosed wombats, combinations of these elements play a substantial role in making the treatment of an already difficult disease more complex. (Moroni et al. Parasit Vectors 13:471, 2020) comment that any pharmacological treatment of free-ranging wildlife must consider these factors when assessing their feasibility and implications, especially in the context of emerging drug resistance and potential long-term ecological impacts. As individuals with significant interest in sarcoptic mange and representing a range of professional research and veterinary expertise, we see value in providing expert commentary on this issue.

Sheep scab spatial distribution: the roles of transmission pathways

BACKGROUND

Ovine psoroptic mange (sheep scab) is a highly pathogenic contagious infection caused by the mite Psoroptes ovis. Following 21 years in which scab was eradicated in the UK, it was inadvertently reintroduced in 1972 and, despite the implementation of a range of control methods, its prevalence increased steadily thereafter. Recent reports of resistance to macrocyclic lactone treatments may further exacerbate control problems. A better understanding of the factors that facilitate its transmission are required to allow improved management of this disease. Transmission of infection occurs within and between contiguous sheep farms via infected sheep-to-sheep or sheep-environment contact and through long-distance movements of infected sheep, such as through markets.

METHODS

A stochastic metapopulation model was used to investigate the impact of different transmission routes on the spatial pattern of outbreaks. A range of model scenarios were considered following the initial infection of a cluster of highly connected contiguous farms.

RESULTS

Scab spreads between clusters of neighbouring contiguous farms after introduction but when long-distance movements are excluded, infection then self-limits spatially at boundaries where farm connectivity is low. Inclusion of long-distance movements is required to generate the national patterns of disease spread observed.

CONCLUSIONS

Preventing the movement of scab infested sheep through sales and markets is essential for any national management programme. If effective movement control can be implemented, regional control in geographic areas where farm densities are high would allow more focussed cost-effective scab management.

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.

Sheep scab transmission: a spatially explicit dynamic metapopulation model

Psoroptic mange (sheep scab), caused by the parasitic mite, Psoroptes ovis, is an important disease of sheep worldwide. It causes chronic animal welfare issues and economic losses. Eradication of scab has proved impossible in many sheep-rearing areas and recent reports of resistance to macrocyclic lactones, a key class of parasiticide, highlight the importance of improving approaches to scab management. To allow this, the current study aimed to develop a stochastic spatial metapopulation model for sheep scab transmission which can be adapted for use in any geographical region, exhibited here using data for Great Britain. The model uses agricultural survey and sheep movement data to geo-reference farms and capture realistic movement patterns. Reported data on sheep scab outbreaks from 1973 to 1991 were used for model fitting with Sequential Monte Carlo Approximate Bayesian Computation methods. The outbreak incidence predicted by the model was from the same statistical distribution as the reported outbreak data (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\chi }^{2}$$\end{document}χ2 = 115.3, p = 1) and the spatial location of sheep scab outbreaks predicted was positively correlated with the observed outbreak data by county (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau$$\end{document}τ = 0.55, p < 0.001), confirming that the model developed is able to accurately capture the number of farms infected in a year, the seasonality of scab incidence and the spatial patterns seen in the data. This model gives insight into the transmission dynamics of sheep scab and will allow the exploration of more effective control strategies.

Doramectin efficacy against Psoroptes ovis in sheep: Evaluation of pharmacological strategies

The aims of this study were to evaluate the efficacy of two injectable formulations of doramectin (DRM) against Psoroptes ovis in sheep infested under controlled experimental conditions and to characterize the DRM plasma disposition kinetics in the infested animals. To this end, sheep were experimentally infested with a P. ovis strain from a farm with a history of treatment failure, and then treated either with DRM 1% (traditional preparation) on days 0 and 7 or with DRM 3.15% (long-acting formulation) on day 0. The efficacy of each treatment was calculated by counting live mites in skin scrapings. Plasma samples were obtained from each animal and DRM concentrations were measured by HPLC. After the two doses of DRM 1%, the maximum efficacy (98.8%) was reached on day 28, whereas after the single dose of DRM 3.15%, the maximum efficacy (100%) was reached on day 35 and ratified on day 42. The long-acting formulation allowed obtaining higher exposure and more sustained concentrations of DRM than the traditional preparation. Although both DRM formulations studied were effective according to international protocols, they did not reach 100% effectiveness in the time required for approved pharmaceutical products against sheep scab, according to Argentine regulations.

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.

Uptake of Diagnostic Tests by Livestock Farmers: A Stochastic Game Theory Approach

Game theory examines strategic decision-making in situations of conflict, cooperation, and coordination. It has become an established tool in economics, psychology and political science, and more recently has been applied to disease control. Used to examine vaccination uptake in human medicine, game theory shows that when vaccination is voluntary some individuals will choose to "free-ride" on the protection provided by others, resulting in insufficient coverage for control of a vaccine-preventable disease. Here, we use game theory to examine farmer uptake of a new diagnostic ELISA test for sheep scab-a highly infectious disease with an estimated cost exceeding £8M per year to the UK industry. The stochastic game models decisions made by neighboring farmers when deciding whether to adopt the newly available test, which can detect subclinical infestation. A key element of the stochastic game framework is that it allows multiple states. Depending on infestation status and test adoption decisions in the previous year, a farm may be at high, medium or low risk of infestation this year-a status which influences the decision the farmer makes and the farmer payoffs. Ultimately, each farmer's decision depends on the costs of using the diagnostic test vs. the benefits of enhanced disease control, which may only accrue in the longer term. The extent to which a farmer values short-term over long-term benefits reflects external factors such as inflation or individual characteristics such as patience. Our results show that when using realistic parameters and with a test cost around 50% more than the current clinical diagnosis, the test will be adopted in the high-risk state, but not in the low-risk state. For the medium risk state, test adoption will depend on whether the farmer takes a long-term or short-term view. We show that these outcomes are relatively robust to change in test costs and, moreover, that whilst the farmers adopting the test would not expect to see large gains in profitability, substantial reduction in sheep scab (and associated welfare implications) could be achieved in a cost-neutral way to the industry.