How does west nile virus spread?

Mosquitoes: Summer and early fall. It does not seem to be catching person-to-person.

By Mosquitoe: West nile virus must be produced in high numbers before being passed through mosquitoes. Birds are far and away the most frequent carriers. Robins look like they might be responsible for spread all over the country. Mosquitoes have to feed on the infected robin and then pass the virus on to human beings through a bite.