Mosquitoes and West Nile Virus

In the United States, West Nile virus (WNV) is transmitted through the bite of infected mosquitoes, primarily members of the Culex genus. In Fairfax County, the primary vector of WNV is Culex restuans. This mosquito feeds primarily on birds and serves to disseminate the virus in the bird population. The bridge vector of WNV in Fairfax County is Culex pipiens. This mosquito will feed upon both birds and humans and in so doing may transmit the virus to the human population.

These two species of mosquito are virtually impossible to distinguish with the naked eye. Both are small brownish mosquitoes, as seen below.


Culex Culex Mosquito laying eggs

Culex mosquito laying eggs. Photo courtesy of the Centers for Disease Control and Prevention (CDC).

Of growing concern is the Asian Tiger Mosquito, Aedes albopictus, a mosquito that has proven to be a severe nuisance species and will certainly become an unwanted pest once it is established near your home. This mosquito is a container breeder and is often closely associated with homes. This mosquito is small and may be identified by the striking black and white pattern on its legs and white stripe on its back, as seen below.

Picture of Asian Tiger Mosquito

Aedes albopictus,the Asian Tiger Mosquito. Photo courtesy of CDC.

Because of the preferred breeding sites and the aggressive nature of this mosquito, its potential to transmit WNV is a great concern. However, the public health importance of this mosquito remains undetermined. The potential for Ae. albopictus to transmit certain pathogenic arboviruses indigenous to the United States has been proven in laboratory experiments; however, disease transmission by this mosquito in natural settings has not been documented. To date, there have been two positive Aedes albopictus pools collected in Fairfax County. Both occurred in 2003.

Learn about mosquito surveillance in Fairfax County.

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