Distribution and Phylogenetic Comparisons of a Novel Mosquito Flavivirus Sequence Present in Culex tarsalis Mosquitoes from Western Canada with Viruses Isolated in California and Colorado

In a previous study, a new flavivirus genome sequence was identified in Culex tarsalis mosquitoes obtained in Alberta, Canada and was shown to be genetically related to but distinct from members of the insect-specific flaviviruses. Nonstructural protein 5–encoding sequences amplified from Cx. tarsalis pools from western Canada have shown a high similarity to genome sequences of novel flaviviruses isolated from mosquitoes in California and Colorado. Despite wide distribution of this virus, designated Calbertado virus, strains demonstrate a high degree of nonstructural protein 5 nucleotide (> 90%) and amino acid (> 97%) identity. The ecology and geographic range of Calbertado virus warrants further study because it may potentially influence transmission of mosquito-borne flaviviruses, including important human pathogens such as West Nile and Saint Louis encephalitis viruses

Insect-Specific Flaviviruses from Culex Mosquitoes in Colorado, with Evidence of Vertical Transmission

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