A vaccine already approved in the United States to prevent a related disease protects experimental animals and may also protect people from the most serious complication associated with West Nile virus infection, say researchers from the University of Texas Medical Branch at Galveston (UTMB).
They report their findings today at the 50th Annual Meeting of the American Society of Tropical Medicine and Hygiene in Atlanta.
Dr. Robert Tesh, a professor in the Center for Tropical Diseases at UTMB and his colleagues tested two vaccines for Japanese encephalitis (JE) for their its ability to protect hamsters from the fatal encephalitis (inflammation of the brain) that is associated with West Nile viral infection.
The JE virus is a flavivirus, a member of the same viral family as the West Nile virus, dengue virus and St. Louis encephalitis virus.
"It looks like the West Nile virus is spreading throughout the Western Hemisphere and it will probably go all the way through the tropics and down to Argentina” says Tesh.
“In the United States we haven't had much exposure to flaviviruses; but we wanted to see what could happen when the West Nile virus reached an area like Central America where people have already had exposure to other flaviviruses, either through infection or vaccination.”
Previous studies in India have suggested that prior infection with the JE virus will protect monkeys from fatal West Nile infections. In this study Tesh and his colleagues first inoculated hamsters with one of three flavivirus vaccines: a live-attenuated JE vaccine currently used on millions of people in China, a killed-virus JE vaccine currently approved for use in the United States and a yellow fever vaccine.
"If we infect hamsters with the New York strain of West Nile virus about half will die of encephalitis if they have not had a previous flavivirus infection," says Tesh. But in the case of the JE-vaccinated hamsters "none of them died and they had lower levels of virus in their blood”. The best protection was provided by the JE vaccines. The yellow fever vaccine protected the hamsters partially, but not as well.
While this research shows that the vaccine works in hamsters, Tesh cautions that evidence is lacking on whether it will work in humans. The next step would be to test its effectiveness in primates. He also points out that the experimental infection was given to the hamsters one month after vaccination and that no research has yet been done on the duration of the protection.
While that is an additional area of study, he notes that the JE killed vaccine probably does not give lifetime protection against JE in humans. "With the JE killed vaccine, every few years you get a booster," Tesh says.
"Although further testing is needed, our preliminary results in hamsters suggest that two widely used Japanese encephalitis (JE) vaccines might be used as interim vaccines to protect high risk human populations against West Nile encephalitis until a suitable West Nile virus-specific vaccine becomes available."