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Progress on potential vaccine against West Nile virus
Edward R. Winstead


Scientists have created a genetically modified virus that protects mice against infection by the West Nile virus. Mice inoculated with the modified virus—a combination, or chimera, of two viruses—survived lethal exposures to virulent strains without apparent negative effects. The chimera virus can now be tested in horses and other animals as a potential human vaccine. Currently no vaccine is available.

The Culex quinquefasciatus mosquito can transmit the West Nile virus.

In the new study, researchers created a potential vaccine strain by inserting two proteins from a West Nile (WN) virus into the genome of another virus—dengue virus type 4 (DEN4). The resulting chimera stimulated an immune response in mice that was sufficient to protect against infection by virulent strains of the WN virus. Alexander G. Pletnev, of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, led the research.

The "chimera and a deletion mutant derived from it were immunogenic and provided complete protection against lethal WN challenge," the researchers write in Proceedings of the National Academy of Sciences. "These observations provide the basis for pursuing the development of a live attenuated WN vaccine."

Humans and animals including horses and birds develop forms of West Nile disease. The most serious type is fatal encephalitis, which is an inflammation of the brain. During the nineties, the virus caused outbreaks of encephalitis in Algeria, Romania, the Czech Republic, the Democratic Republic of the Congo, and Russia. More recent outbreaks have occurred in Israel and the United States, where the virus has spread to new regions.

The WN virus belongs to a family of more than 60 flaviviruses and is transmitted to humans via mosquito. It was first isolated from a woman in the West Nile District of Uganda in 1937. In the early 1960s, the disease was first reported in horses in Egypt and France. The appearance of the virus in North America in 1999, which led to encephalitis in humans and horses, "may be an important milestone in the evolving history of this virus," according to the US Centers for Disease Control and Prevention.

For more information on the West Nile virus visit the US Centers for Disease Control and Prevention.

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Pletnev, A.G. et al. West Nile virus/dengue type 4 virus chimeras that are reduced in neurovirulence and peripheral virulence without loss of immunogenicity or protective efficacy. Proc Natl Acad Sci USA 99, 3036-3041 (March 5, 2002).

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