Which genus of mosquitoes are major vectors of West Nile and St. Louis Encephalitis in the U.S.?

The genus Culex is recognized as a major vector for both West Nile virus and St. Louis Encephalitis in the United States. Culex mosquitoes, particularly species such as Culex pipiens, are known to thrive in urban environments and are often associated with stagnant water sources where they breed. These mosquitoes have a significant role in the transmission of these viruses because they feed preferentially on birds, which serve as reservoirs for these arboviruses. When Culex mosquitoes bite infected birds, they can acquire the virus, which then replicates within the mosquito until it reaches a level sufficient for transmission to humans and other animals.

In contrast, although other mosquito genera like Aedes, Anopheles, and Psorophora can transmit various diseases, they are not the primary vectors for West Nile virus or St. Louis Encephalitis in the U.S. Aedes mosquitoes are more commonly associated with diseases like dengue and Zika, while Anopheles is the primary vector for malaria, and Psorophora has a lesser role in disease transmission overall compared to Culex. Therefore, Culex is specifically highlighted due to its significant public health impact related to these encephalitic diseases.