Virology 2008 May 18;374(2):256-60. Epub 2008 Apr 18.
Wadsworth Center, New York State Department of Health, 5668 State Farm Rd. Slingerlands, NY 12159, USA.
To investigate differential evolutionary rates and selective forces of WNV in hosts and vectors, we measured the genetic diversity that arose during alternating passage in mosquitoes and birds. Within-host genetic diversity was monitored in each of three experimentally passed replicates, and the complete genome sequence of each WNV strain was determined after passage. The intrahost genetic diversity that arose during alternating passage was significantly greater than the diversity generated during chicken-only passage and similar to mosquito-only passage. dN/dS ratios suggested purifying selection similar to chick-passed virus, but not to mosquito-passed virus. Thus, the abundant genetic variation contributed to WNV populations through infection of mosquitoes and the strong purifying selection contributed by infection of birds may be maintained despite frequent host switching.