RALEIGH, N.C. (AP) -- The West Nile virus killed two people and sickened two dozen more in North Carolina just four years ago.
Now scientists are trying to figure out why the disease that originated along the Atlantic coast has migrated west.
North Carolina has seen fewer than five cases of West Nile virus each year since 2003. None of those have been fatal.
The mosquito-borne disease has been flourishing in the West. California is preparing for its deadliest year ever.
West Nile spreads when mosquitoes feed on infected birds and then bite humans.
Some scientists say North Carolina has been spared because most of the birds susceptible to infection have possibly died off. But others say its likely because North Carolina doesn't have many mosquitoes that feed on both birds or humans.
State officials still say people should remain on guard in case the virus returns.
(Copyright 2007 by The Associated Press. All Rights Reserved.)