There is no reason to be concerned that feeding birds in your back yard will increase your risk of exposure to the West Nile Virus. No evidence of bird-to-person transmission has been reported.
West Nile virus is transmitted by mosquitoes, which contract the virus from infected birds then pass the disease to humans. Crows seem to be one of the most commonly infected bird species, and the virus is particularly deadly to them. Often the first harbinger that West Nile is entering an area is an increase in the number of dead birds, especially crows, who have been infected with the disease. CDC along with state and local health officials monitor the number of infected birds carefully.
Because mosquitoes spread the disease, it is important to eliminate places where they breed. Change the water in your birdbaths daily and empty any standing water in flowerpots, pool covers and clogged rain gutters that may host mosquito larvae.