Abstract
BackgroundIn the last two decades, recurrent epizootics of bluetongue virus and Schmallenberg virus have been reported in the western Palearctic region. These viruses affect domestic cattle, sheep, goats and wild ruminants and are transmitted by native hematophagous midges of the genus Culicoides (Diptera: Ceratopogonidae). Culicoides dispersal is known to be stratified, i.e. due to a combination of dispersal processes occurring actively at short distances and passively or semi-actively at long distances, allowing individuals to jump hundreds of kilometers.MethodsHere, we aim to identify the environmental factors that promote or limit gene flow of Culicoides obsoletus, an abundant and widespread vector species in Europe, using an innovative framework integrating spatial, population genetics and statistical approaches. A total of 348 individuals were sampled in 46 sites in France and were genotyped using 13 newly designed microsatellite markers.ResultsWe found low genetic differentiation and a weak population structure for C. obsoletus across the country. Using three complementary inter-individual genetic distances, we did not detect any significant isolation by distance, but did detect significant anisotropic isolation by distance on a north-south axis. We employed a multiple regression on distance matrices approach to investigate the correlation between genetic and environmental distances. Among all the environmental factors that were tested, only cattle density seems to have an impact on C. obsoletus gene flow.ConclusionsThe high dispersal capacity of C. obsoletus over land found in the present study calls for a re-evaluation of the impact of Culicoides on virus dispersal, and highlights the urgent need to better integrate molecular, spatial and statistical information to guide vector-borne disease control.Graphical
Highlights
In the last two decades, recurrent epizootics of bluetongue virus and Schmallenberg virus have been reported in the western Palearctic region
Characterization of microsatellite markers and genetic diversity A total of 368 c oxidase (COI) sequences of C. obsoletus were obtained after the DNA barcoding step (Additional file 3: Table S3), and 368 C. obsoletus from 46 populations were genotyped with 13 microsatellite loci (Additional file 4: Table S4)
This study shows that the genetic structure of populations at the scale of a country can become homogeneous through large-scale dispersion
Summary
In the last two decades, recurrent epizootics of bluetongue virus and Schmallenberg virus have been reported in the western Palearctic region These viruses affect domestic cattle, sheep, goats and wild ruminants and are transmitted by native hematophagous midges of the genus Culicoides (Diptera: Ceratopogonidae). Northern Europe experienced very sudden and rapid outbreaks of bluetongue virus (BTV) in 2006–2008 and Schmallenberg virus (SBV) in 2011–2012 [4] Both viruses have spread very quickly and widely across the whole western Palearctic region transmitted by native Culicoides species. Culicoides obsoletus has been identified as the main vector species responsible for the transmission of BTV and SBV to wild and domestic ruminants in the western Palearctic region [5,6,7]. High ambient temperatures reduce the incubation period of the virus [15], whereas high precipitation and wind speeds can reduce Culicoides flight activity [16,17,18]
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