Abstract:
Biological phenotypes of tri-segmented arboviruses display characteristics that map to mutation/s in the S, M or L segments
of the genome. Plaque variants have been characterized for other viruses displaying varied phenotypes including
attenuation in growth and/or pathogenesis. In order to characterize variants of Bunyamwera and Ngari viruses, we isolated
individual plaque size variants; small plaque (SP) and large plaque (LP) and determined in vitro growth properties and in vivo
pathogenesis in suckling mice. We performed gene sequencing to identify mutations that may be responsible for the
observed phenotype. The LP generally replicated faster than the SP and the difference in growth rate was more pronounced
in Bunyamwera virus isolates. Ngari virus isolates were more conserved with few point mutations compared to Bunyamwera
virus isolates which displayed mutations in all three genome segments but majority were silent mutations. Contrary to
expectation, the SP of Bunyamwera virus killed suckling mice significantly earlier than the LP. The LP attenuation may
probably be due to a non-synonymous substitution (T858I) that mapped within the active site of the L protein. In this study,
we identify natural mutations whose exact role in growth and pathogenesis need to be determined through site directed
mutagenesis studies.
