Embedded Player The West Nile virus was identified for the first time in Uganda in the 1930s. It was infecting people in the West Nile region of Africa. The virus spreads when mosquitoes bite infected animals, and then bite humans. It showed up for the first time in the United States two summers ago. In 1999, thousands of crows around New York City, infected with the virus, began dropping dead out of the sky and dozens of people ended up in hospitals. Now a federal study, which has not been published, suggests that since it arrived in the U.S., the West Nile virus has made roughly 1,400 people sick. It has spread from New York and now is known to infect animals along the East Coast, up to the Canadian border and down to North Carolina. It is expected to eventually spread across the entire United States. NPR's Daniel Zwerdling reports the case of West Nile symbolizes a dilemma: as the global economy knits countries closer together, it's also making the United States more vulnerable to exotic diseases. The story of West Nile is a production of NPR and American Radio Works. It was produced by Marisa Penaloza.