Having struck nearly 2,100 people and killed 98 in the United States so far this year, West Nile virus infection amounts to an epidemic. Now, medical workers have found poliolike symptoms in a few victims, and last week, federal officials said that blood transfusions appear to have infected some people.
The first U.S. cases of West Nile fever were reported in 1999 in New York. Since then, it's hit 35 other states. The disease is generally transmitted by mosquitoes.
Though flulike symptoms are most common, some severe cases progress to encephalitis, a potentially fatal swelling of the brain, occurs. Two reports to be published in the Oct. 17 New England Journal of Medicine link the virus to rare instances of long-term paralysis, a symptom that had shown up in birds, horses, and monkeys.