It's mosquito season, and that means the West Nile virus is back. The Midwest outbreak this summer is the worst in US history, with 50 deaths so far in Texas alone. Fewer people have gotten sick in California, but the disease showed up here earlier than usual. And scientists are concerned that as the climate warms, West Nile and other mosquito-borne illnesses will gain a stronger foothold here. Reporter Molly Samuel explains.