By Sophie Bushwick(Click here for the original article and podcast)West Nile virus first appeared in North America in 1999. And it quickly moved across the continent. Now a study has pinned the proliferation on a particular culprit: robins. The work is published in the journal Science. [A. Marm Kilpatrick, "Globalization, Land Use, and the Invasion of West Nile Virus"] Read More... More on Video