West Nile Virus numbers are spiking nationwide. Is global warming driving the outbreak? And is the U.S in line for more tropical disease?

It’s a wild season, already, for West Nile virus. Before 1999, we’d never seen it in the U.S. It was a scourge out of Uganda. Africa. Now, it’s all over the United States. 2012 is shaping up as likely the worst season ever. 700-plus cases already. Dozens dead. Cities spraying. Dallas has declared a state of emergency. And lifestyles are changing as Americans shrink from mosquitoes, dusk, dawn.

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