Climate Affects WNV Transmission

Some years are worse than others for West Nile virus transmission. Changes in temperature affect both the mosquito life cycle and virus replication in different hosts. The mild winter, early spring, and hot summer of 2012 are thought to have contributed to the increase in West Nile virus cases.

A map of the United States titled Temperatures April 2012. White equals near normal. Yellow-orange equals above normal. Orange equals much above normal. The great lakes region, Washington, and California are white. Most of the rest of the country is yellow-orange. Much of New England and the Great Plains are orange. — April 2012 temperature departures from normal for the contiguous U.S.