West Nile Virus Transmission
“Mosquitoes that maintain WNV in the enzootic cycle are members of the Culex genus, Culex pipiens, Culex quinquefasciatus, and Culex tarsalis are the primary vectors of WNV. Dr. Kramer says that one of the challenges in understanding the ecology of WNV is that different mosquito species serve as vectors of the virus in different regions of the country. For example, Culex pipiens transmits the virus in the northeast and central United States. Culex tarsalis carries the virus from the far west to the panhandle of Texas. Culex quinquefasciatus carries the virus in the southeastern USA from Texas to Florida.
Culex pipiens feeds almost exclusively on birds. So, transmission of WNV to mammals in the northern United States requires a bridge vector—i.e., a mosquito that feeds on both birds and mammals. Bridge vectors for Culex pipiens include Culex salinarius , Ochlerotatus japonicus , and Aedes albopictus . Alternatively, Culex quinquefasciatus and Culex tarsalis feed on both birds and mammals.So, in the South and the West, where there is no need for a separate bridge vector, the virus may spread more quickly.”
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