"Although the prevalence of West Nile virus disease fluctuates seasonally and regionally, it continues to pose a serious public health threat, especially to older adults and people with weakened immune systems," says Anthony S. Fauci, M.D., director of the NIAID.
WNV, initially isolated in Uganda in 1937, made its first U.S. appearance in New York City in 1999. The virus usually is transmitted to humans through the bite of a mosquito that has been infected after feeding on an infected bird or animal. The virus also can be spread through blood transfusions, organ transplants and breastfeeding, as well as from mother to child during pregnancy. Most people experience no symptoms or only mild symptoms, such as fever, headache and body aches; more serious cases can lead to infections of the brain and nervous system, such as encephalitis or meningitis. In 2004, 2,470 cases of WNV disease were reported in the United States, resulting in 88 deaths. Currently, no WNV vaccine is licensed for use in humans.
The experimental vaccine is composed of a small, circular piece of DNA--called a DNA plasmid--that contains genes that code for two key surface proteins of the West Nile virus. When the vaccine is injected into the muscle, the inner machinery of the muscle cells "reads" the DNA and converts it into two WNV proteins. Recognizing that the proteins are foreign, the muscle cells display