Date of Award




Document Type

Master's Thesis

Degree Name

Master of Science (MS)


Department of Biomedical Sciences

Content Description

1 online resource (v, 70 pages) : illustrations (some color)

Dissertation/Thesis Chair

Laura D Kramer

Committee Members

Janice D Pata, Kirsten St.George


Flavivirus, Polymerase fidelity, Ribavirin, RNA dependent RNA polymerase, St. Louis encephalitis virus, Saint Louis encephalitis, West Nile virus, RNA polymerases, Virus-vector relationships

Subject Categories



St. Louis encephalitis virus (SLEV) is mosquito-borne member of the family Flaviviridae, genus Flavivirus that is closely related to West Nile virus (WNV). Both viruses have potential to cause neuroinvasive disease in humans, and currently there is no vaccine or approved antiviral therapy. SLEV is maintained in nature through transmission between mosquitoes and birds, with humans acting as dead-end hosts. Despite their genetic and antigenic similarities, WNV and SLEV display different characteristics. WNV is known as a "generalist"; it is geographically widespread and can infect a wide variety of hosts, causing over 37,000 human cases in 48 U.S. states since 1999. SLEV, however, is more restricted in its distribution, maintaining low levels of activity and geographic isolation. Both are positive-strand RNA viruses, encoding an RNA-dependent RNA polymerase (RdRp) responsible for genome replication. RNA viruses have a high mutation rate (~10-4) that correlates to approximately 1 mutation per SLEV genome copied. Because of this high error rate, RNA viruses typically exist as quasispecies or complex swarms of mutant viruses within the host, and it is postulated that this mutant swarm may facilitate transmission of arboviruses in different tissues and disparate hosts. It has therefore been hypothesized that polymerase fidelity may be associated with viral fitness, virulence, and pathogenesis in RNA viruses, specifically arboviruses, and that increased polymerase fidelity can cause attenuation in certain hosts. The relationships between polymerase fidelity, the capacity to generate genetic diversity, and its effects on viral adaptation and pathogenesis have not been studied previously in flaviviruses. Here, the mutagen ribavirin was used to select for ribavirin-resistant SLEV populations that shared a single E416K amino acid mutation in the RdRp. In vitro phenotypic effects were analyzed in vertebrate and invertebrate cell lines. Replicative fitness of the resistant populations was not affected, and population diversity was lower than the wildtype virus in both host cell types. These results suggest that these SLEV variants displayed a higher-fidelity phenotype. This work will provide important information to aid further research into the mechanisms behind differing epidemiologic and genetic patterns seen between SLEV and WNV, despite their similar enzootic cycles and genome conservation.

Included in

Virology Commons