Immunization with vaccine strains of flaviviruses that are antigenically related to the West Nile virus (WNV) can protect animals following WNV challenge, researchers report.
Dr. Robert B. Tesh and colleagues, from the University of Texas in Galveston, immunized hamsters with a live attenuated Japanese encephalitis virus (JEV) vaccine, a wild-type St. Louis encephalitis virus (SLEV), or a live attenuated Yellow fever virus (YFV) vaccine and then tested their response to challenge with the WNV 30 days later.
The researchers' findings are published in the March issue of Emerging Infectious Diseases. Vaccination with JEV or SLEV protected the animals from clinical encephalitis and death, the researchers note. YFV vaccination afforded only partial protection. Four of 30 YFV-immune animals died compared with 14 of 30 unvaccinated control animals.
"We were interested in observing the effect that preexisting flavivirus antibodies would have on WNV challenge," Dr. Tesh told Reuters Health. "Previous reports have suggested that antibodies to some of the related flaviviruses may offer protection against WNV," he said.
"JEV- or SLEV-immunized animals became infected with WNV, but the level of viremia was much lower than in control animals," Dr. Tesh noted. "Furthermore, none of the JEV- or SLEV-vaccinated animals died," he added.
"I live close to Houston, and St. Louis encephalitis virus is endemic in this part of the country," Dr. Tesh said. "We were wondering what might happen if the West Nile virus came to this area," he added. "Our findings suggest that a bird with SLEV may not be a good amplifying host for WNV, and therefore it would be less likely to pass the virus to mosquitos."