Serological diagnosis of West Nile virus.

States would not have known of the existence of a flavivirus known as West Nile virus (WNV). Indeed, most clinical microbiologists and medical laboratory scientists, would only have had a limited knowledge of the virus. All that has changed in the last three to four years. In 1999, WNV emerged in New York and from there has spread to most of the continental United States, with successive seasons seeing the migration of the infection north, south, and west from the New York epicenter. WNV has a broad host range, including birds (the primary host), humans, and other animals. Indeed, WNV has had a significant health and economic impact on horses and industries dependent upon horses, such as horse racing. That birds are the primary host of WNV is important to the understanding of the importation and spread of the virus. As based on available evidence, the New York outbreak appears to have resulted from the importation of WNV via viremic migratory birds, with an isolate from a dead bird in New York being closely related to a 1998 isolate of WNV from a goose in Israel.