Defra - Department for Environment, Food and Rural Affairs.

Science Search

Science and Research Projects

Return to Science Search homepage   Return to Project List

Sheep Scab Host Parasite Interactions - OD0556

Sheep scab, caused by the mite Psoroptes ovis is, arguably, the most important ectoparasitic disease of sheep in the UK and is endemic in the national flock. The disease is highly contagious, causing severe irritation and is a major welfare concern. It is currently controlled using acaricides. However, because of concerns over residues, environmental contamination and drug resistance, this is unsustainable and alternative control methods are needed.
Prior infestation with sheep scab alters the progression of any subsequent infestations; lesion size and mite numbers are reduced, offering encouragement for vaccination. Research at MRI has focused on identifying and validating vaccine antigens. This has been informed by a better understanding of the host:parasite interaction, leading to the identification of novel vaccine candidates. Immunisation with a vaccine containing 7 of these candidate molecules prior to infestation with P. ovis resulted in a >50% reduction in lesion area and a significant reduction in mite numbers. This represents the greatest reduction in lesion size with a recombinant sheep scab vaccine and provides real encouragement for future production of a commercially viable means of immunoprophylaxis and we now aim to build upon this success by improving efficacy. P. ovis excretes/secretes a complex repertoire of molecules, triggering an allergic skin response which characterises the disease and creates an environment conducive to mite survival. Identifying immunomodulatory factors produced by parasites is one of the key areas in vaccinology at MRI. The rationale behind using these factors as vaccine candidates is that, if we produce a neutralising host response against them, we can enhance the protective capacity and efficacy of a vaccine. We will therefore focus on identifying P. ovis immuno-modulators to augment the existing vaccine; characterise the nature of the vaccine-induced protective immune response to understand the mechanisms by which vaccination results in reduced pathology and use this information to optimise vaccine delivery.
Combining a vaccine and a diagnostic test with targeted acaricidal treatment provides the tools necessary to control sheep scab. With funding from Defra, we developed a specific and sensitive diagnostic test. In partnership with Pfizer Animal Health Ltd and the National Farmer’s Union, Scotland, we will validate this test in the field, as part of our ongoing programme, to determine its utility in local and regional eradication campaigns.

Research Aims:
i) Identify and characterise P. ovis immunomodulatory factors as additional/augmentative vaccine candidates.
ii) Further characterise the mechanisms of vaccine-induced protective immunity.
iii) Optimise delivery to stimulate the most appropriate immune response.
iv) Validate the sheep scab diagnostic test in the field.
By developing sustainable methods for the control of sheep scab based on immunoprophylaxis and subclinical diagnosis, the proposed research programme provides a significant contribution to Defra’s aims of ‘Enhancing the competitiveness and resilience of the food chain and ensuring a secure, environmentally sustainable and healthy supply of food with improved standards of animal welfare’. The research also contributes to the Scottish Government’s strategic objectives of ensuring a ‘Healthier, Wealthier and Fairer’ Scotland in ensuring well treated and healthy farm animals in Scotland
Objective 1: Identification and characterisation of P. ovis antigens involved in host immune evasion and immunoregulatory mechanisms to identify alternative/augmentative sheep scab vaccine antigens (July 2013 – April 2016).

Objective 2: P. ovis life cycle stage specific gene expression (September 2013 - August 2014).

Objective 3: Further characterisation of natural protective immunity as a tool for informing the most appropriate mechanisms of a vaccine-induced protective immune response (July 2013 – April 2016).

Objective 4: Identification of gene expression patterns in mites that are able to survive in the face of a mounting and directed host immune response (July 2013 – June 2015).

Objective 5: Epitope mapping of existing vaccine antigens (July 2013 – June 2014).

Objective 6: Presentation of immunogenic epitopes as particulate arrays (December 2013 – November 2014).

Objective 7: Presentation of antigens using an epitheliotropic virus vector (December 2013 - November 2014).

Objective 8: Vaccination and challenge infestation trials (May 2014 – October 2014) and (May 2015 – October 2015).

Objective 9: Vaccine trial analysis and assessment of a vaccine as a useable tool for sheep scab control programmes (July 2015 - April 2016).

Objective 10: Field validation of the existing sheep scab ELISA in the context of a sheep scab eradication scheme on the Isle of Mull, Scotland (July 2013 - June 2015).

Objective 11: Field validation study in the Republic of South Africa (RSA) in the context of a Government funded regional eradication scheme (July 2013 - June 2014).
Time-Scale and Cost
From: 2013

To: 2016

Cost: £760,152
Contractor / Funded Organisations
Moredun Research Institute
Fields of Study
Animal Health