There likely will be West Nile virus activity in the United States this year, and the extent and direction of its spread will be hard to predict. The good news is that researchers have completed studies that might help in the management of the disease.West Nile made its Western Hemisphere debut in the summer and fall of 1999, attacking birds, horses, and humans. Twenty-five equine positives were confirmed in 1999 in the Northeast, followed by 59 positives in 2000.Researchers and public health officials from all over the world joined at an International Conference on West Nile Virus in New York April 5-7. The history of the outbreak of the virus in the United States and other countries was discussed, as well as future implications of the virus.One research group at the conference reported success with a West Nile virus DNA vaccine that protects mice and horses. Another study confirmed that the horse is a dead-end host for the virus, which is spread by mosquitoes.