(Atlanta-AP) -- Health officials warned today that West Nile virus should continue its westward march this summer.
The virus has killed 18 people along the East Coast since showing up in the US three years ago. It's been found as far west as Arkansas and Louisiana on Oklahoma's eastern border.
Health officials say migratory birds will probably carry the virus even farther west this season.
Mosquitoes spread West Nile from infected birds to humans, who can then develop deadly encephalitis, or swelling of the brain. Humans can't pass the virus to each other.
West Nile was first detected in New York in 1999. Last summer was the most severe so far with 66 human infections and nine deaths reported.
No human cases have been identified so far in 2002.