West Nile Evolution: Using Cell Culture Competition Assays to Assess Replicative Fitness.

摘要

West Nile virus (WNV) was first detected in California near El Centro, Imperial County on July 16, 2003. WNV outbreaks in Los Angeles (2004, 2008 and 20012), Sacramento (2005) and Bakersfield (2007) highlighted the need to track the spatio-temporal evolution of WNV, predict WNV movement, and gain a better understanding of the factors that facilitate WNV epidemics. An in vivo fitness competition model was previously developed to study the phenotypic changes in WNV as it adapted to different mosquito vector and avian host systems throughout California. This fitness competition assay allowed us to evaluate the replicative fitness of an unknown strain to a labelled reference strain (a clone derived California founding COAV997-2003 WNV strain) within the same system (host, cell etc.) instead of by concurrent single infections. In this study, we evaluated the replicative fitness of four Coachella Valley isolates, COAV1573_07, COAV1091_08, COAV1333_08 and COAV1722_08 in an avian cell line [duck embryonic fibroblasts (DEF)] and Aedes albopictus-derived C6/36 cell cultures using the same competition fitness model. An in vitro competition fitness model allowed for the rapid screening for relative fitness differences among field strains of WNV against the labelled reference strain. We found that in vitro COAV997-5nt representing the 2003 founding isolate generally outcompeted these more recent isolates of WNV from Coachella Valley. This rapid screening could be useful for research or diagnostic purposes not only for WNV, but other viruses that affect public health, to assess how viruses change to become more or less pathogenic over time.