West Nile virus and the climate

West Nile virus is transmitted by urban-dwelling mosquitoes to birds and ot her animals, with occasional "spillover" to humans. While the means by whic h West Nile virus was introduced into the Americas in 1999 remain unknown, the climatic conditions that amplify diseases that cycle among urban mosqui toes, birds, and humans are warm winters and spring droughts. This informat ion can be useful in generating early warning systems and mobilizing timely and the most environmentally friendly public health interventions. The ext reme weather conditions accompanying long-term climate change may also be c ontributing to the spread of West Nile virus in the United States and Europ e.