Submitted to: Virus Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/29/2002
Publication Date: 10/1/2002
Citation: LLEWELLYN, Z.N., SALMAN, M.D., PAUSZEK, S.J., RODRIGUEZ, L.L. GROWTH AND MOLECULAR EVOLUTION OF NATURAL ISOLATES OF VESICULAR STOMATITIS SEROTYPE NEW JERSEY IN INSECT CELLS. VIRUS RESEARCH. V 89: 65-73, 2002. Interpretive Summary: Vesicular stomatitis virus (VSV) causes a costly disease in livestock that is clinically undistinguishable from foot-and-mouth disease (FMD). Unlike FMD virus, VSV is transmitted by blood-feeding insects such as sand flies. VSV has a very high capacity to genetically change and mutate its proteins. The high mutation rate could have important implications on the appropriate e-ness of current diagnostic methods & vaccine development efforts. This work was aimed at understanding if insect cellular factors played a role in influencing VSV evolution. We determined the growth, persistence and rate of evolution of a VSV-New Jersey isolate (89GAS) in cells derived from its natural vector (sand flies) and compared them with those observed in cells derived from mosquitoes or hamster kidneys which are thought not to be natural hosts for the virus. Our results showed that the sand-fly derived virus grew to higher titers & established persistent infection in sand fly cells. Furthermore, we found evidence that insect cells can influence viru evolution as indicated by amino acid sequence changes induced in the main membrane protein of virus by repeated passage in insect & mammalian cells. These results indicate that insect cells can be a selective factor for VSV evolution in-vitro. However, we could not detect significant differences between rates of evolution of VSV-NJ by passage in homologous (sand fly) versus heterologous (mosquito or mammalian) cells.
Technical Abstract: Despite their high capacity for mutation during in-vitro growth, vesicular stomatitis viruses (VSV) circulating within endemic areas are genetically conserved over long periods of time and one possible selective factor could be the vector(s) involved on its natural cycle. In this study we determined the growth and genetic sequence stability of a viral strain isolated from sand flies (89GAS) during serial passage in sand-fly (LL5), mosquito (C6/3 and mammalian (BHK-21) cells; and compared them with those of strains of equine and bovine origin. Sand fly virus 89GAS grew to higher titers in insect cells than did viruses of mammalian origin. Although all viruses readily established persistent infections both in mosquito & sand fly cells maintained in culture for up to 81 days, sustained virus yields were only observed in sand fly cells. Sequence analyses of the viruses after 0,10 or up to 25 passages in each cell line showed no changes in hypervariable region of phosphoprotein (P) gene or the intergenic junction between the glycoprotein (G) & the polymerase (L). In contrast the G gene demonstrated mutation rates between 1.39x10-4 and 6.95x10-5 in most cell-virus combina- tions. The majority of the mutations were non-synonymous, suggesting positive selection. These results showed that although insect cells can be a selective factor on VSV evolution in-vitro, we could not detect signifi- cant differences between rates of evolution of VSV-NJ by passage in homologous (sand fly) versus heterologous (mosquito or mammalian) cells.