Abstract
BackgroundWest Nile virus (WNV) is an arbovirus of public health importance in the genus Flavivirus, a group of positive sense RNA viruses. The NS3 gene has a high level of substitutions and is phylogenetically informative. Likewise, substitutions in the envelope region have been postulated to enable viruses to subvert immune responses. Analysis of these genes among isolates from positive mosquitoes collected in Louisiana illustrates the variation present in the regions and provides improved insight to a phylogenetic model. Employing a GIS eco-regionalization method, we hypothesized that WNV pool positivity was correlated with regional environmental characteristics. Further, we postulated that the phylogenetic delineations would be associated with variations in regional environmental conditions.ResultsType of regional land cover was a significant effect (p < 0.0001) in the positive pool prediction, indicating that there is an ecological component driving WNV activity. Additionally, month of collection was significant (p < 0.0001); and thus there is a temporal component that contributes to the probability of getting a positive mosquito pool. All virus isolates are of the WNV 2002 lineage. There appears to be some diversity within both forested and wetland areas; and the possibility of a distinct clade in the wetland samples.ConclusionsThe phylogenetic analysis shows that there has been no reversion in Louisiana from the 2002 lineage which replaced the originally introduced strain. Our pool positivity model serves as a basis for future testing, and could direct mosquito control and surveillance efforts. Understanding how land cover and regional ecology effects mosquito pool positivity will greatly help focus mosquito abatement efforts. This would especially help in areas where abatement programs are limited due to either funding or man power. Moreover, understanding how regional environments drive phylogenetic variation will lead to a greater understanding of the interactions between ecology and disease prevalence.
Highlights
West Nile virus (WNV) is an arbovirus of public health importance in the genus Flavivirus, a group of positive sense RNA viruses
There were 611 positives reported by the Louisiana Animal Disease Diagnostic Laboratory, 165 in our target parishes
Our statistical model serves as a basis for future testing, directing mosquito control efforts and surveillance programs
Summary
West Nile virus (WNV) is an arbovirus of public health importance in the genus Flavivirus, a group of positive sense RNA viruses. Substitutions in the envelope region have been postulated to enable viruses to subvert immune responses. Analysis of these genes among isolates from positive mosquitoes collected in Louisiana illustrates the variation present in the regions and provides improved insight to a phylogenetic model. WNV was introduced into the United States in 1999 and from its entry point of New York City it spread across the continental United States. Phylogenetic evidence traced this strain to a similar strain isolated in Israel in 1998 [2]. The number of deaths from 1999-2001 were significantly less than the number of deaths in 2002 alone, though whether this association is due to direct virulence in humans or an indirect result of the virulence in birds remains unclear [1,3,4]
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