West Nile Neurologic Disease Gaining Ground: In some states, the incidence of WNV encephalitis is at least 25-fold greater than herpes encephalitis.

VAIL, COLO. â€" West Nile virus has very quickly become the most important cause of arbovirus encephalitis in the United States. West Nile virus (WNV) first appeared in the Western Hemisphere in New York City in 1999. Yet today the overall frequency of West Nile encephalitis in the United States approaches that of herpes simplex encephalitis, Dr. Kenneth L. Tyler observed at a conference on pediatric infectious diseases sponsored by the Children's Hospital, Denver.