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. 2011 Jul;85(1):169-77.
doi: 10.4269/ajtmh.2011.10-0474.

Insect-specific flaviviruses from Culex mosquitoes in Colorado, with evidence of vertical transmission

Bethany G Bolling  1 , Lars Eisen, Chester G Moore, Carol D Blair
Affiliations

Insect-specific flaviviruses from Culex mosquitoes in Colorado, with evidence of vertical transmission

Bethany G Bolling et al. Am J Trop Med Hyg. 2011 Jul.

Abstract

Mosquitoes were collected in Colorado during 2006 and 2007 to examine spatial and seasonal patterns of risk for exposure to Culex vectors and West Nile virus. We used universal flavivirus primers to test pools of Culex mosquitoes for viral RNA. This led to the detection and subsequent isolation of two insect-specific flaviviruses: Culex flavivirus (CxFV), which was first described from Japan, and a novel insect flavivirus, designated Calbertado virus (CLBOV), which has also been detected in California and Canada. We recorded both viruses in Cx. tarsalis and Cx. pipiens from Colorado. Furthermore, quantitative reverse transcription polymerase chain reaction (RT-PCR) revealed the presence of CxFV RNA in Cx. pipiens eggs and larvae from a laboratory colony established in 2005 and naturally infected with CxFV, suggesting vertical transmission as a means of viral maintenance in natural Culex populations. Finally, we present phylogenetic analyses of the relationships between insect-specific flaviviruses and other selected flaviviruses.

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Figures

Figure 1.
Figure 1.
Location of mosquito sampling sites for 2006 (along the Cache la Poudre River) and 2007 (along the Big Thompson River and South Platte River). The location of the targeted five-county area in Colorado is shown in the inset map.
Figure 2.
Figure 2.
Monthly infection rates from June to September 2007 for Cx. tarsalis (A–C) and Cx. pipiens (D–F) with WNV (A and D), CxFV (B and E), and CLBOV (C and F). Error bars indicate 95% skewness-corrected confidence intervals. Estimates for infection rates per 1,000 mosquitoes were calculated with Excel Add-In PooledInfRate 3.0.
Figure 3.
Figure 3.
Phylogenetic tree inferred from Bayesian analysis and midpoint rooted, showing relationships between insect-specific flaviviruses from Culex species mosquitoes collected in Colorado (shaded) and other flaviviruses based on a 1-kb segment of the NS5 gene. The numbers at the nodes represent clade credibility values and the scale bar indicates the number of estimated substitutions per site. GenBank accession numbers for the sequences used in the analysis are listed in parentheses.
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