Genetic analysis of West Nile virus isolates from US blood donors during 2002-2005.

BACKGROUND

Since its introduction into North America in 1999, West Nile virus (WNV) has spread rapidly across United States (US).

OBJECTIVE

To genetically analyze WNV isolates from US blood donors during 2002-2005.

STUDY

DESIGN

Full-length nucleotide (NT) sequences of WNV isolates from 23 US volunteer blood donors of different geographic areas from 2002 to 2005 were determined and analyzed.

RESULTS

Results indicated an overall lack of geographic pattern to WNV in US. Analyses of the viral genetic diversity demonstrated that the WNV evolved at approximately five NT substitutions and 0.8 amino acid (AA) mutations per genome per year. Comparison of the functional sequences of WNV genome showed a higher evolution rate in the coding region than in the non-coding region. Furthermore, a greater diversity was observed in the nonstructural proteins as compared to the structural proteins. Sequence alignment analysis revealed that the rapid spread of WNV in US was accompanied by the establishment of a dominant genetic variant with 11 conserved NT mutations.

CONCLUSIONS

The establishment of a dominant genotype across US and the displacement and possible extinction of earlier progenitor genotypes appears to have resulted from the accumulation and fixation of 11 nucleotide mutations throughout the coding region of WNV genome.