The Epidemiology and Surveillance of Culicoides-borne Diseases of Ruminants in the UK

Jessica Eleanor Stokes
PhD Thesis Culicoides biting midges Schmallenberg virus Bluetongue


Between 2006 and 2011 two Culicoides-borne diseases of ruminants emerged in Europe: bluetongue virus serotype-8 (BTV-8) and Schmallenberg virus (SBV). This thesis sought to answer questions arising from this developing disease landscape, to better inform policymakers, stakeholder groups and disease modellers.

SBV spread rapidly through Europe, reaching the UK in January 2012. However, in 2014 no cases were reported. It was unknown if this was a lack of circulation, or a lack of reporting. A freedom from disease study was designed. 1444 sheep, born between October 2014 and April 2015, were sampled from 131 farms from Cornwall to Kent. Samples were tested by ELISA for antibodies against SBV, 5 positive samples were confirmed negative by VNT. Circulation of SBV in 2015 in the south of England was concluded to have been unlikely.

Like SBV, BTV-8 had circulated throughout Europe, only to be controlled by movement restrictions and vaccination. Subsequently, Europe was declared BTV-8 free in 2010 and vaccination production halted. In 2015 BTV-8 re-emerged in Europe. An online questionnaire determined that respondents from smaller farms, those that had previously vaccinated against BTV-8 and those who were deemed to be ‘risk adverse’ were all more likely to want to vaccinate, and more willing to pay more to vaccinate. Voluntary vaccination only achieved an 80% uptake if vaccination was free and after BTV-8 cases were reported in the UK despite 90% of farmer respondents stating they believed it important to keep BTV-8 out of the UK. Not all farmers vaccinated all of their flock/herd previously. This survey highlights the complex issues surrounding voluntary vaccination at the farm perceived risk versus cost level.

The mechanisms for how either virus successfully overwintered are still poorly understood. A cross-sectional study demonstrated that Culicoides vectors are active during peak lambing periods inside lambing sheds. A longitudinal study the following lambing season demonstrated that Culicoides were more abundant indoors than outdoors, and demonstrated activity of gravid and parous Culicoides over the winter. This demonstrates a possible mechanism for overwintering of BTV-8 and SBV in the south of England.

SBV re-emerged in 2016. A questionnaire was designed to determine the impact of SBV on the 2016/2017 lambing period. The impact was found to be highly comparable to a previous study of the 2012/2013 outbreak. Additionally SBV confirmed and suspected farms were more likely to have mated earlier in the season. If SBV continues to re-emerge cyclically then the impact of disease will continue to be significant unless intervention is taken.

These studies have added to our understanding of, and farmer response to, the SBV and BTV-8 outbreaks, and added to policymakers, stakeholders groups and disease modellers knowledge.