This is from the North Carolina State University - Department of Entomology.

Question: Does the presence of Cx. quinquefasciatus (one of the two common biters) in large numbers greatly
increase the risk of a localized outbreak of West Nile encephalitis? 

Answer: This question is not easy to answer. Preliminary
studies of Cx. Pipiens (the biter common to our neighbourhood), the species closely related to Cx. quinquefasciatus, 
suggest they are not the most efficient vector of the West Nile virus (Turell et al., 2000).
Eighty percent of Cx. pipiens exposed to the virus may become infected, but only about 20 percent of those are able
to transmit the virus to other hosts. As promising as this information seems, it is too soon to
know if Cx. quinquefasciatus plays a major role in the transmission of West Nile virus. Different geographical 
populations of the two closely related Culex species may be more or less efficient vectors of West Nile
virus . The prudent decision is to assume that the risk is great enough to be sure mosquito control 
Best Management Practices are in place for waste lagoons. 

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