What is the vector for West Nile virus?

The correct answer identifies Culex mosquitoes as the vector for West Nile virus because these mosquitoes are the primary species responsible for transmitting the virus to humans and other animals. When a Culex mosquito feeds on the blood of an infected bird, it can acquire the virus and subsequently transmit it during future blood meals. This transmission cycle mainly involves birds, which serve as the reservoir for the virus.

In contrast, other options do not serve as vectors for West Nile virus. Ticks are known vectors for other diseases but are not associated with the transmission of West Nile virus. House flies do not have the capability to transmit the virus. Aedes mosquitoes, while known for transmitting other viruses such as Zika and dengue, are not the primary or effective vectors for West Nile virus. Thus, Culex mosquitoes play a crucial role in the epidemiology of West Nile virus, making them the correct answer in this context.