west nile virus

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West Nile Virus and the Future of Once-Tropical Diseases

Midwest outbreak is the worst in U.S. history — and may be a sign of things to come

Molly Samuel/KQED

Mosquitoes under a microscope at the Sacramento-Yolo Mosquito and Vector Control District.

William Reisen began studying tropical diseases when he was drafted in the Vietnam War. He’d studied insects in school, so he worked as an entomologist for the Air Force. Eventually, his career led him to California, where he now heads UC Davis’s Center for Vectorborne Diseases. But even with his professional experience with mosquito-borne diseases, he says he never expected to see West Nile virus in the United States.

“Everybody was surprised,” he says. “If you were a betting person, and you wanted to guess the next virus that would cause trouble from abroad in North America, I think few of us would have expected West Nile.”

West Nile, a disease carried by birds and spread by mosquitoes, first made inroads in the U.S. in 1999, in New York. By 2003, it had reached California. In 2004 and 2005, there were hundreds of human cases; in those two years combined, 48 people in California died. Continue reading