Abstract:
Bluetongue virus (BTV), a segmented dsRNA virus, is the causative agent of bluetongue
(BT), an economically important viral haemorrhagic disease of ruminants. Bluetongue virus
can exchange its genome segments in mammalian or insect cells that have been co-infected
with more than one strain of the virus. This process, may potentially give rise to the
generation of novel reassortant strains that may differ from parental strains in regards to their
phenotypic characteristics. To investigate the potential effects of reassortment on the virus’
phenotype, parental as well as reassortant strains of BTV serotype 1, 6, 8, that were derived
from attenuated, and wild type strains by reverse genetics, were studied in vitro for their virus
replication kinetics and cytopathogenicity in mammalian (Vero) cell cultures. The results
indicate that genetic reassortment can affect viral replication kinetics, the cytopathogenicity
and extent/mechanism of cell death in infected cell cultures. In particular, some reassortants
of non-virulent vaccine (BTV-1 and BTV-6) and virulent field origin (BTV-8) demonstrate
more pronounced cytopathic effects compared to their parental strains. Some reassortant
strains in addition replicated to high titres in vitro despite being composed of genome
segments from slow and fast replicating parental strains. The latter result may have
implications for the level of viraemia in the mammalian host and subsequent uptake and
transmission of reassortant strains (and their genome segments) by Culicoides vectors.
Increased rates of CPE induction could further suggest a higher virulence for reassortant
strains in vivo. Overall, these findings raise questions in regards to the use of modified-live
virus (MLV) vaccines and risk of reassortment in the field. To further address these
questions, additional experimental infection studies using insects and/or animal models
should be conducted, to determine whether these results have significant implications in vivo.
