Field experiments on live attenuated Japanese encephalitis virus vaccine for swine.

The efficacy of a live attenuated Japanese encephalitis virus (JEV) vaccine was examined in swine under conditions where natural infection could occur. The pigs immunized with the vaccine produced antibodies within one week after vaccination, and the antibody was retained until the end of the experiment, i.e. 36 days. However, the antibody titers in this group were lower than that in control group naturally infected with JEV. No virus was isolated from the five vaccinated pigs, but virus was isolated from all four untreated control pigs after natural infection, i.e., viremia was detected in all these animals. The duration of viremia in control pigs varied from one to four days. From these findings, it is concluded that immunization of swine with live attentuated JEV vaccine is useful in control of Japanese encephalitis (JE) in humans and some susceptible domestic animals.