A vaccine developed by Yale scientists has protected mice from the West Nile virus, a mosquito-borne infection that has been linked to about 10 deaths in the United States since the summer of 1999.

The virus, first identified in Uganda in 1937, surfaced in the New York City area in 1999 and has subsequently appeared in the South and Midwest. It is considered an emerging disease, said Erol Fikrig, M.D., associate professor of medicine and of epidemiology and public health. “Its seriousness as a public health threat is not fully known yet,” said Fikrig, who directed the development of the vaccine. “That should become apparent over the next two to three years. If the vaccine proves necessary, its development will be valuable.”

The virus, which infects birds as well as humans, spreads through mosquito bites primarily in warm-weather months. There is currently no cure, although infection does not generally cause serious consequences. Elderly patients, however, can develop fatal encephalitis, a central nervous system infection.

Fikrig and colleagues, including Tian Wang, Ph.D., a postdoctoral fellow in his laboratory, and John F. Anderson, Ph.D., research affiliate in epidemiology, and associates from the Connecticut Agricultural Experiment Station in New Haven, isolated a sample of the virus found in an infected bird. They genetically engineered a protein in the virus, which they then injected into uninfected mice. Immunization with the vaccine provided complete protection for the mice against West Nile virus.

Because diagnosis of West Nile virus can be difficult using current methods, the protein used to make the vaccine could also be employed to develop a diagnostic test, Fikrig said.

Results of the study were published online in the Journal of Immunology on October 23 and appeared in the November 1 print issue.