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Vector-borne transmission pathways and serological diagnostics of Schmallenberg virus - SE0542

Schmallenberg virus (SBV) is a novel Orthobunyavirus that has recently been identified as circulating in sheep and cattle across a broad area of the north-western Palaearctic region, including the UK. Phylogenetic comparisons of the SBV genome place this pathogen within the Simbu serogroup, which are widely distributed worldwide and are primarily transmitted by arthropod vectors (primarily biting midges and mosquitoes). The impact of SBV occurs primarily through congenital defects in young born to infected dams. In offspring, the main clinical signs of SBV are congenital malformations (severe arthrogryposis, torticollis, brachygnathia, hydrocephalus and other severe brain malformations), similar to those observed in infections by the related Akabane virus (AKAV). Heavy infection of the central nervous system by SBV has been observed in infected offspring. Infection in adult ruminants appears to lead to mild, but observable clinical signs (e.g. pyrexia, mucous diarrhea, loss of appetite and reduction in milk yield). Current knowledge suggests that it is unlikely that Schmallenberg virus can cause disease in humans.

Transmission of SBV by vectors has yet to be confirmed since the initial outbreaks of the virus and this generates significant uncertainty in the policy response employed. In this proposal we will characterize the replication, dissemination and transmission of SBV across a wide variety of putative vectors using techniques developed at IAH for this purpose under previous Defra grants. If it is confirmed that SBV is vector-borne, we will also investigate the probability of overwintering of the virus in the arthropod host by assessing the probability of transovarial transmission and by examining the extrinsic incubation period in comparison to bluetongue virus (BTV) for which a large amount of resources are already in place to aid policy response. Results will be communicated to Defra on a rolling basis to aid in achieving rapid responses to data collected.

A second current gap in knowledge concerning SBV is the lack of a suitable high throughput and sensitive assay to detect specific antibodies in animals that have previously been infected buy the virus. We intend to develop such an assay based on either a competition/blocking ELISA format, or a Luminex assay, using recombinant expressed SBV proteins and monoclonal antibodies. Using these reagents which have no potential for contamination with the original virus, the resulting assay would have no disease security restrictions concerning the movement and sharing of reagents. Consequently such an assay could be rapidly shared with colleagues in other laboratories.
Objective 1. To carry out intrathoracic inoculation studies in one species of Culicoides and mosquito line that will characterize the ability of Schmallenberg virus (SBV) to replicate in the haemocoel of putative vector species and allow full dissemination to be defined.
Objective 2. To carry out membrane feeding assays that will allow assessment of infection, dissemination and transmission potential of SBV in three lines (two species) of mosquitoes and two species of Culicoides.
Objective 3. To conduct studies to estimate the extrinsic incubation period of SBV in putative vector species identified through (1) and (2) and compare to data already collected for BTV.
Objective 4. To conduct a preliminary investigation into transovarial transmission of SBV in putative vector species.
Objective 5. To produce a suitable high-throughput and sensitive assay for detection of SBV specific antibodies in animals previously infected by the virus.
Project Documents
• EVID4 - Final project report : SE0542 Final report -final   (658k)
Time-Scale and Cost
From: 2012

To: 2012

Cost: £114,636
Contractor / Funded Organisations
The Pirbright Institute (TPI)
Disease Control              
Fields of Study
Animal Health