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

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.

Evidence of extensive renewed Schmallenberg virus circulation in Belgium during summer of 2016 - increase in arthrogryposis-hydranencephaly cases expected

“…Despite the examination of a higher number of midges in July (49 pools–980 midges) and September (31 pools–620 midges), no SBV‐positive pools were found at those time points. Our results therefore confirm that entomological SBV surveillance is an important non‐invasive surveillance method but that it must be done on a continuous basis in order not to miss the mostly short‐lived virus circulation in a specific region (De Regge et al., ; Kameke, Werner, Hoffmann, Lutz, & Kampen, ).…”

Culicoides monitoring in Belgium in 2011: analysis of spatiotemporal abundance, species diversity and Schmallenberg virus detection

“…It also correlates with the relatively lower within‐herd seroprevalence found in sheep and cows in this region at the end of the vector season of 2011 (Méroc et al ., , ). The finding of high numbers of SBV‐positive midges at Libramont during the vector season of 2012, when the prevalence of infection in Avaritia midges was found to be 2.86% in August (De Regge et al ., ), supports this hypothesis.…”

Preparation and characterization of a stable BHK-21 cell line constitutively expressing the Schmallenberg virus nucleocapsid protein

“…Infection of pregnant animals with SBV during a critical period of gestation can result in abortions, fetal malformations or stillbirths [5,8,9]. Certain Culicoides biting midges have been demonstrated to be the main vector for SBV transmission [10,11]. SBV can also be vertically transmitted from mother to fetus through the placenta [8,12e14].…”