... from the folks at Reuters, so you might want to take with a grain of salt or two... http://www.reuters.com/article/healthNews/idUSN0327118820080703 New West Nile virus strain may worsen epidemic Thu Jul 3, 2008 5:31pm EDT By Maggie Fox, Health and Science Editor WASHINGTON (Reuters) - A new strain of West Nile virus is spreading better and earlier across the United States, and may thrive in hot American summers, researchers said on Thursday. The virus infected an estimated 175,000 people last year, the U.S. Centers for Disease Control and Prevention reported in its weekly report on death and disease on Thursday. The mosquito-borne virus caused an estimated 35,000 cases of fever, was reported to have killed 117 people and caused serious disease such as encephalitis and meningitis in 1,227 people in 2007, the CDC reported. A second team of researchers said a new strain of the virus that has completely overtaken the original strain is particularly well suited to hotter weather -- which in turn means West Nile outbreaks may worsen in the north. It also means that North America may suffer more from West Nile virus than other parts of the world, said Lyle Petersen, who helps lead West Nile surveillance at the CDC... ...West Nile was introduced to the United States in 1999 -- during a particularly hot summer in New York City. The new strain appears to have evolved naturally, said Petersen. "We can no longer find the 1999 strain. It's pretty dramatic," he said. The Kilpatrick findings fit in with what the CDC has seen, Petersen added. "What we observed is, at least in temperate climates, these big West Nile Virus outbreaks tend to occur in heat waves," Petersen added. (Editing by Will Dunham) © Thomson Reuters 2008. All rights reserved.