West Nile fever: lessons from the 2002 season.

West Nile fever has now spread to much of the United States. This disease can be diagnosed using one of several laboratory tests, notably an immunoglobulin M enzyme-linked immunosorbent assay. It can cause devastating neurologic damage, including an unusual polio-like syndrome. Magnetic resonance imaging is an important imaging tool in such patients. Treatment is largely supportive, although antiviral agents are under investigation.