Understanding the immune mechanism of host disease resistance and development of marker vaccines and DIVA tests for Peste des Petits Ruminants (PPR)

点击翻译按钮获取中文摘要

Peste des petits ruminants (PPR), also known as 'goat plague', is a highly contagious viral disease of sheep and goats. The direct economic losses of this disease have been estimated to be INR 1800 million (US$ 39 million) annually in India alone, whilst globally, >60% of the small ruminant population is considered at risk. However little is known about the pathogenesis of PPRV. Importantly, the primary site of viral replication has yet to be properly defined and the mechanism of the contrasting host specific disease resistance to PPR is unknown. Effective live attenuated vaccines are available to control PPR and a c-ELISA kit, to monitor the antibody response against the H protein, has been developed at IVRI and Pirbright. However, the critical drawback of these vaccines and associated c-ELISA kits is their inability to differentiate infection in vaccinated animals (DIVA) that slows down the implementation of PPR control through vaccination. We hypothesise that PPRV infects immune cells of the respiratory mucosa, which then migrate to T-cell-rich areas of local lymphoid organs, from which virus enters the general circulation. We aim to develop a recombinant live attenuated DIVA vaccine that will be aerosolised to the primary viral replication site and is capable of generating a rapid and appropriate immune response including mucosal immunity. By further characterising the immune mechanisms underlying the differential susceptibility of sheep, goats and large ruminants to PPRV infection we aim to enhance our understanding of disease resistance mechanisms that will enable the development of better vaccines for the control of PPRV.Aims and objectives: Three complementary research objectives are necessary to advance the ability to control and eradicate PPR: 1) understand PPRV pathogenesis in the pre-viraemic stage to identify the primary site of virus replication as a target for vaccination; 2) further characterise the immune response to PPR in small and large ruminants to understand differential disease resistance; and 3) develop appropriate PPR marker vaccines with associated DIVA tests to provide effective and targeted PPR control, ultimately leading to eradication from India. Research approaches: Similar to our Nigeria75/1 GFP vaccine virus rescue, a virulent recombinant PPR virus containing the GFP gene will be constructed and rescued. This virus will be aerosolised to infect goats. Tissues will be collected from respiratory mucosa and associated lymph nodes and the primary viral replication site will be located by auto fluorescence of GFP and by IHC in tissues. Subsequent vaccinations will use the intranasal route if we define the primary replication site of PPRV during the pre-viremic stage. Using reverse genetics techniques we will develop two negative marker vaccines against Indian PPRV (Sungri 96- goat origin and Arasur 1987- sheep origin). Epitope deletion of a region of the H protein critical for monoclonal antibody binding will allow serological differentiation between vaccinated and naturally infected animals using the current cH-ELISA. For simple and rapid field diagnosis, we intend to develop loop mediated isothermal amplification assay (LAMP) and a lateral flow device. Real-time RT-PCR assay and biosensor assay development and validation in India will help the PPR control programme. Interrogation of the immune mechanisms that underlie the differential susceptibility of species / breeds of small and large ruminants to PPRV will be carried forward using an unbiased transcriptomics approach. Increasing our knowledge on early pathogenesis, using a marker vaccine to generate an appropriate immune response and the ability to differentiate infection from vaccination, in combination with a deeper understanding of immune function will enable the control of PPRV. This project will help in delivering PPR control in India and elsewhere by bringing together major players in PPR research in India and the UK.