Schmallenberg virus circulation in culicoides in Belgium in 2012: field validation of a real time RT-PCR approach to assess virus replication and dissemination in midges

PLoS One. 2014 Jan 23;9(1):e87005. doi: 10.1371/journal.pone.0087005. eCollection 2014.

Abstract

Indigenous Culicoides biting midges are suggested to be putative vectors for the recently emerged Schmallenberg virus (SBV) based on SBV RNA detection in field-caught midges. Furthermore, SBV replication and dissemination has been evidenced in C. sonorensis under laboratory conditions. After SBV had been detected in Culicoides biting midges from Belgium in August 2011, it spread all over the country by the end of 2011, as evidenced by very high between-herd seroprevalence rates in sheep and cattle. This study investigated if a renewed SBV circulation in midges occurred in 2012 in the context of high seroprevalence in the animal host population and evaluated if a recently proposed realtime RT-PCR approach that is meant to allow assessing the vector competence of Culicoides for SBV and bluetongue virus under laboratory conditions was applicable to field-caught midges. Therefore midges caught with 12 OVI traps in four different regions in Belgium between May and November 2012, were morphologically identified, age graded, pooled and tested for the presence of SBV RNA by realtime RT-PCR. The results demonstrate that although no SBV could be detected in nulliparous midges caught in May 2012, a renewed but short lived circulation of SBV in parous midges belonging to the subgenus Avaritia occured in August 2012 at all four regions. The infection prevalence reached up to 2.86% in the south of Belgium, the region where a lower seroprevalence was found at the end of 2011 than in the rest of the country. Furthermore, a frequency analysis of the Ct values obtained for 31 SBV-S segment positive pools of Avaritia midges showed a clear bimodal distribution with peaks of Ct values between 21-24 and 33-36. This closely resembles the laboratory results obtained for SBV infection of C. sonorensis and implicates indigenous midges belonging to the subgenus Avaritia as competent vectors for SBV.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Belgium
  • Bunyaviridae Infections / genetics
  • Bunyaviridae Infections / transmission*
  • Bunyaviridae Infections / virology
  • Ceratopogonidae / virology*
  • Insect Vectors / virology*
  • Orthobunyavirus / classification
  • Orthobunyavirus / genetics
  • Orthobunyavirus / isolation & purification*
  • RNA, Viral / genetics*
  • Real-Time Polymerase Chain Reaction
  • Reverse Transcriptase Polymerase Chain Reaction
  • Virus Replication / genetics*

Substances

  • RNA, Viral

Grants and funding

Monitoring of Culicoides in Belgium in 2012 was financed by the Belgian Federal Agency for the Safety of the Food Chain (FAVV-AFSCA). rRT-PCR analysis of Culicoides for presence of SBV was funded by the Federal Public Service of Health, Food Chain Safety and Environment (RF12/6270) and the European Union as outlined in Council Decision 2012/349/EU concerning a financial contribution by the Union for studies on Schmallenberg virus. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.