"The first year or two, it was mostly in New York and New Jersey, but now it's working its way south," health commissioner Peter Beilenson said.
The city planned to spray chemical permethrin, a commonly used crop pesticide, in Clifton Park in the northeastern section of the city on Tuesday night, Beilenson said.
Seventy-seven dead birds infected with the virus have been found since May 15 in that section of the city. Maryland leads the nation in the number of birds testing positive for the virus this year, state officials have said.
West Nile causes only a flu-like sickness for some people, but can be life-threatening for the elderly. The virus appeared in the Western Hemisphere in 1999 when 59 people were hospitalized with encephalitis or meningitis and seven died.
Last year, 21 human West Nile cases were reported, two of them fatal, according to the U.S. Centers for Disease Control and Prevention. There have been no human cases reported in Maryland.
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