Scientists closing in on West Nile virus vaccine

WASHINGTON – U.S. government scientists have developed a hybrid vaccine that protects mice from West Nile virus infection.

The vaccine consists of a weakened combination of two viruses formed by removing key genes from dengue virus and replacing them with West Nile virus genes. Researchers will begin testing the vaccine in monkeys next month and hope to begin human trials in late 2002.

West Nile virus occurs in many parts of the world. In 1999, it arrived in New York to make its first North American appearance. Infected birds have since been found as far west as Arkansas and Illinois.

The virus can cause human illness, and although it usually causes only mild symptoms, it can spread to the central nervous system and cause a potentially deadly brain inflammation called encephalitis. To date, the virus has killed seven people and caused severe disease in more than 80 others, mostly elderly people.

Combination. By combining the two viruses, scientists accomplished two major goals. First, because the hybrid vaccine consisted mostly of dengue virus, which does not target the central nervous system, the engineered virus does not infect the brain.

Second, the addition of select West Nile virus genes causes the hybrid to stimulate strong anti-West Nile virus immune responses, even following a single dose of the vaccine. When injected into mice, the vaccine protected all of the immunized animals from subsequent exposure to the New York West Nile virus strain.

One of the dengue viruses used by the researchers to construct the genetic backbone of the hybrid virus had already been proven safe in people.