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Orbivirus molecular epidemiology studies and development of diagnostic assay systems - SE2619

Bluetongue virus (BTV) is transmitted by Culicoides biting midges and causes a haemorhagic disease, bluetongue (BT), in susceptible ruminant hosts. The outbreaks of BTV-8 that occurred in the UK during 2007 demonstrated that BTV can cause serious disruption to ruminant trade and production. Later outbreaks of BTV-1 in northern France have additionally demonstrated that the BTV-8 incursion was not an isolated occurrence. While both these BTV strains have been eradicated across the EU using coordinated vaccination campaigns, there remains a need to be able to identify drivers that may influence epidemiological parameters of strains threatening the UK. In this project we examine the process of re-assortment of BTV genome segments in both the Culicoides and ruminant host with a view to identifying those factors that might influence the UK policy response to incursion (e.g. pathogenicity; transmission by northern European Culicoides; thermal requirements for replication). Secondly, we examine the potential for using novel technologies to investigate overwintering of BTV in the Culicoides host which may influence the probability of a given strain successfully persisting in the UK.
All identified serotypes of BTV share a genome structure that allows exchange of segments following co-infection of host or vector cells, a process termed reassortment. Recent studies carried out by IAH and others have demonstrated that reassortment occurs in the field with far higher regularity than previously thought, having been largely overlooked prior to the advent of multi-segment sequencing of viruses. The importance of reassortment is that by exchange of genome segments, new progeny strains can be created which may inherit epidemiological characteristics from either parent strain. Our workplan will utilise entomology, virology and molecular biology to define the behaviour of BTV parental and reassortant strains in both ruminant hosts and Culicoides. This will provide information regarding the potential for policy relevant changes in the epidemiology of BTV strains following reassortant events including changes in primary vector species, adaptation to northern European temperatures and pathogenicity to livestock. It will also address fundamental questions of relevance in understanding the global distribution of BTV and the persistence of the virus in areas of incursion.
The potential for transovarial overwintering of BTV in Culicoides has been investigated previously both in the USA and in the UK (the latter as part of a previous Defra funded project: SE2610). While live virus has never been isolated from progeny insects during previous experiments, the most recent studies used PCR-based techniques to demonstrate the presence of BTV proteins in larvae collected in the field in the USA. It was hypothesised that core particles of BTV were transmissible between life history stages and that this could be a novel form of overwintering for BTV. These field findings have not been confirmed using controlled laboratory studies. The confirmation or negation of transovarial transmission as an overwintering method through detailed studies will enable a narrowing of alternative scenarios in the event of a future incursion.
1: Maintain and expand the Orbivirus Reference Collection (providing materials for sequencing studies, as well as diagnostic assay and vaccine development).
2: Extend the existing sequence database for whole genomes of ‘reference’ BTV isolates representing different serotypes and topotypes (from around the world).
3: Generate and analyze whole genome sequence data for existing and new BTV isolates/serotypes from Europe and surrounding areas, for studies of molecular epidemiology and genome segment reassortment.
4: Generate genome sequence data for representative isolates of each of the 22 different Orbivirus species, providing reference data for novel isolate identification, differential diagnosis and analyses of genetic relationships.
5: Design a generic RT-PCR assays to detect and identify any orbivirus (see objective 4)
6: Design (and maintain) oligonucleotide primers and probes, for real-time RT PCR assays to detect to identify each of the 26 BTV types (see objectives 2 and 3).
7: Design (and maintain) oligonucleotide primers and probes, for real-time RT PCR assays to detect and identify each of the 9 AHSV types and the 7 EHDV serotypes.
8: Design RT-PCR assays to detect individual Orbivirus species (species-specific/group-specific assays).
9: Evaluate primers and probes and provide relevant assays to the Non-vesicular Reference Laboratory at IAH Pirbright.
Time-Scale and Cost
From: 2012

To: 2016

Cost: £972,087
Contractor / Funded Organisations
IAH - Institute for Animal Health
Fields of Study
Animal Health