Abstract
Bluetongue virus serotypes 1 to 24 are transmitted primarily by infected Culicoides midges, in which they also replicate. However, “atypical” BTV serotypes (BTV-25, -26, -27 and -28) have recently been identified that do not infect and replicate in adult Culicoides, or a Culicoides derived cell line (KC cells). These atypical viruses are transmitted horizontally by direct contact between infected and susceptible hosts (primarily small ruminants) causing only mild clinical signs, although the exact transmission mechanisms involved have yet to be determined. We used reverse genetics to generate a strain of BTV-1 (BTV-1 RGC7) which is less virulent, infecting IFNAR(−/−) mice without killing them. Reassortant viruses were also engineered, using the BTV-1 RGC7 genetic backbone, containing individual genome segments derived from BTV-26. These reassortant viruses were used to explore the genetic control of horizontal transmission (HT) in the IFNAR(−/−) mouse model. Previous studies showed that genome segments 1, 2 and 3 restrict infection of Culicoides cells, along with a minor role for segment 7. The current study demonstrates that genome segments 2, 5 and 10 of BTV-26 (coding for proteins VP2, NS1 and NS3/NS3a/NS5, respectively) are individually sufficient to promote HT.
Highlights
Bluetongue is an arboviral disease of ruminants, caused by Bluetongue virus (BTV), the type species of genus Orbivirus
Orbiviruses are transmitted between susceptible hosts by the bites of vector competent, hematophagous arthropods, vectors have not been identified for all orbiviruses [1]
Plasmid clones corresponding to the 10 genome segments of BTV-1RGC7 were purified by miniprep (Figure 2)
Summary
Bluetongue is an arboviral disease of ruminants, caused by Bluetongue virus (BTV), the type species of genus Orbivirus. Most strains of BTV are transmitted between their ruminant hosts via the bites of infected adult female midges (Culicoides spp.). They can infect a number of competent Culicoides species [2], including colony derived adult. More than 36 distinct serotypes of BTV have been isolated from ruminants including sheep, cattle and goats [3]. BTV serotype is determined by the virus outer capsid and cell attachment protein VP2 (encoded by genome segment 2), which elicits neutralising antibodies in infected vertebrate hosts [4,5,6]. Since 2008, several atypical BTV serotypes have been isolated (primarily from small ruminants, including goats or sheep) that do not
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