The Evolution of Pest Control Tarantula Hawk West nile virus threat Continues Well Into the Fall West Nile Virus (WNV) infection is a potentially serious illness transmitted to. WNV is known to infect birds and other animals as well as humans.. It is considered a seasonal epidemic that flares up in the summer and continues into the fall.. In regions of the U.S. with warm climates, workers are at risk for a longer period.