ATLANTA - Health officials warned Thursday that West Nile virus, which has killed 18 people along the East Coast since it surfaced in the U.S. three years ago, should continue its westward march this summer. <br>
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The Centers for Disease Control and Prevention said that inSouthern states, where balmy weather often stretches well into the fall, the virus is coming closer to year-round transmission. <br>
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Mosquitoes spread West Nile from infected birds to humans, who can then develop deadly encephalitis, or swelling of the brain. Humans cannot pass the virus to each other. <br>
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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. <br>
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Sporadic infections have been detected as far west as Illinois, Arkansas and Louisiana, and health officials say migratory birds will probably carry the virus even farther west this season. <br>
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No human cases have been identified so far in 2002.
