Which species is the primary vector and primary reservoir of SLE?

• A. Cx. pipiens
• B. Cx. tarsalis and wild birds
• C. Cs. incidens
• D. Psorophora coloumbiae

Answer: (B)

Saint Louis encephalitis virus is maintained in nature by a bird–mosquito cycle, with birds acting as the reservoir where the virus is amplified and mosquitoes transmitting it to other birds. The mosquito species most often responsible for spreading the virus to birds in many regions is Culex tarsalis, making it the primary vector. Therefore, identifying Culex tarsalis as the main vector along with wild birds as the main reservoir best captures the natural transmission dynamics of SLE.

Other species listed can bite birds or mammals but do not play the central role in maintaining and spreading SLE in the same way. Cs. incidens and Psorophora coloumbiae are not the principal vectors, and while Cx. pipiens can transmit SLE in some settings, it is not considered the primary combination described here.