Which Mosquitoes Carry West Nile Virus?

Despite the lack of a vaccine, West Nile Virus has spread to more than 48 contiguous states and Canada, causing serious neurological disease. Symptoms usually appear within four to ten days of mosquito bite, but more severe illness, such as meningitis or encephalitis, can occur.

The genus flaviviruses includes more than 70 viruses, which can be classified into several serocomplexes. In the Northern Hemisphere, Culex mosquitoes transmit encephalitic flaviviruses. These viruses are known to coevolve with mosquito vectors to coopt unique activities of the insect’s saliva.

Among the mosquitoes that carry WNV in the United States are Aedes albopictus, Aedes aegypti, and Culex tarsalis. Aedes albopictus and Aedes aegypti are common in lower-Midwest regions. Aedes aegypti is also a common mosquito in the mid-Atlantic and southern United States.

In the western United States, the primary vectors of WNV are Culex quinquefasciatus and Culex thriambus. These mosquitoes feed on a variety of avian species. Crows are not a large part of the mosquito’s diet, but their presence may have some effect on transmission.

Using mice, researchers studied the effects of a single mosquito bite on the development of WNV infection. They found that after a single mosquito bite, the mice were more likely to develop neuroinvasion. In addition, they observed higher tissue titers and viremia after a single mosquito bite. The research also suggested that a complex nature of mosquito saliva may enhance early infection.

Aedes aegypti has been shown to control DENV infection through a mechanism called Toll signaling. This pathway has also been found to limit alphavirus infection in Aedes and Anopheles mosquitoes.