ABSTRACT
We report the arthropod-borne pediatric encephalitic agent La Crosse virus in Aedes albopictus mosquitoes collected in Dallas County, Texas, USA, in August 2009. The presence of this virus in an invasive vector species within a region that lies outside the virus's historically recognized geographic range is of public health concern.
Subject(s)
Aedes/virology , Insect Vectors/virology , La Crosse virus/isolation & purification , Animals , Chlorocebus aethiops , Cricetinae , Encephalitis, California/epidemiology , Encephalitis, California/virology , Geography , Humans , La Crosse virus/genetics , Phylogeny , Public Health , RNA, Viral/genetics , RNA, Viral/isolation & purification , Sequence Analysis, RNA , Texas/epidemiology , Vero CellsABSTRACT
In 2012, Texas experienced the largest outbreak of human West Nile encephalitis (WNE) since the introduction of West Nile virus (WNV) in 2002. Despite the large number of WNV infections, data indicated the rate of reported WNE among human cases was no higher than in previous years. To determine whether the increase in WNV human cases could have been caused by viral genetic changes, the complete genomes of 17 isolates made from mosquito pools in Dallas and Montgomery Counties in 2012 were sequenced. The 2012 Texas isolates were found to be composed of two distinct clades, both circulating in Dallas and Montgomery Counties despite a 5-fold higher disease incidence in the former. Although minor genetic differences existed between Dallas and Montgomery WNV populations, there was weak support for population subdivision or adaptive changes. On the basis of these data, alternative explanations for increased WNV disease incidence in 2012 are proposed.
Subject(s)
Disease Outbreaks/statistics & numerical data , West Nile Fever/epidemiology , West Nile Fever/virology , West Nile virus/genetics , Base Sequence , Genetic Variation , Genotype , Humans , Incidence , Likelihood Functions , Mutation , Phylogeny , RNA, Viral/genetics , Sequence Alignment , Sequence Analysis , Texas/epidemiology , West Nile virus/classificationABSTRACT
Analysis of partial nucleotide sequences of 22 West Nile virus (WNV) isolates collected during the summer and fall of 2001 and 2002 indicated genetic variation among strains circulating in geographically distinct regions of the United States and continued divergence from isolates collected in the northeastern United States during 1999 and 2000. Sequence analysis of a 2,004-nucleotide region showed that 14 isolates shared two nucleotide mutations and one amino acid substitution when they were compared with the prototype WN-NY99 strain, with 10 of these isolates sharing an additional nucleotide mutation. In comparison, isolates collected from coastal regions of southeast Texas shared the following differences from WN-NY99: five nucleotide mutations and one amino acid substitution. The maximum nucleotide divergence of the 22 isolates from WN-NY99 was 0.35% (mean = 0.18%). These results show the geographic clustering of genetically similar WNV isolates and the possible emergence of a dominant variant circulating across much of the United States during 2002.