West Nile Virus marches on

Officials are chasing a moving target as the progression of West NileVirus (WNV) penetrates farther west.

The encephalitis strain, which first appeared in the United States in1999, has spread to 15 states plus the District of Columbia. In the pasttwo years, WNV has spread along the Atlantic coast and has been detectedin many birds, horses and at least nine humans from New England to Florida.

"The rest of the continental U.S. will be at risk if the virus expandsto the Caribbean and Central and South America, which is a likely event,"says Robert McLean, DVM, director of the U.S. Geological Survey NationalWildlife Health Center.

"The worst does not appear to be over if the virus expands to southernlocations, where it could be transmitted throughout the year," addsMcLean, who spoke on the virus at the recently concluded AVMA annual convention.

Because WNV arrived on the scene earlier than in previous summers, governmentagencies such as the Centers for Disease Control and the U.S. GeologicalSurvey are stressing the importance of state surveillance programs.

Ohio and at least 17 other state health departments send birds to a U.S.Geological Survey laboratory in Madison, Wis. The federal agency has offeredto analyze tissue samples for free.