Evaluation of Japanese encephalitis virus vaccine strains currently used in pigs by molecular characterization

Abstract

Japanese encephalitis virus (JEV) is one of the main causes of viral encephalitis in human and animals. For over 30 years, a live attenuated JEV vaccine strain has been used in the veterinary field, and it is required to conduct quality evaluation studies on the commercial vaccines. For the quality control of live attenuated JEV vaccine, we investigated the nucleotide sequence similarity of prME gene derived from five JEV vaccines commercially available in pigs in Korea. The Vero cells infected with JEV vaccines showed specific cytopathic effect, which was characterized by rounding and detached cells. In the phylogenetic analysis, all of the vaccine strains showed a close relationship with the original vaccine seed strain (Anyang 300) and clustered into the genotype 3. In comparison of the nucleotide and deduced amino acid sequences of prME genes with the original strain, all JEV vaccine strains showed high amino acid similarity ranging from 98.9% to 99.5%, but had several point mutations, probably due to high mutation rates of viral RNA polymerase by several virus passages. Even though the current JEV vaccine strains have been maintained and produced for a long period of time, the genetic characterization of them have been rarely changed. However, since the mid 1990's, molecular epidemiology of JEV has been changed sharply from genotype 3 to genotype 1 in Korea, further studies on new vaccine strains to genotype 1 is required for more effective prevention in the field.

The present and future of veterinary vaccines for Japanese encephalitis in Korea

“…When the genome sequence of the vaccine strain was compared with those of other JEV strains, it was grouped with G3 viruses. At the nucleotide level, it showed high homology with other G3 viruses but differed clearly from G1 viruses [ 26 ]. At the start of the 3'-untranslated region, the genome of G3 viruses is characterized by specific nucleotide insertions right after the stop codon [ 16 ].…”

Re-Examining the Importance of Pigs in the Transmission of Japanese Encephalitis Virus

“…Despite the potential for reproductive disease and JEV-infected pigs as a source for epizootic spillover, there are currently no licensed JEV vaccines for pigs. There are only regionally approved vaccines, including live attenuated at222, ML17, and anyang300 vaccines, that are available for local use in Japan, China, and Korea [ 27 , 48 , 62 , 63 ]. While reduction in JE disease and viremia in swine may be possible through pig immunization, it is important to understand that vaccination of domestic pigs cannot be solely relied upon to prevent the risk of human JEV infection and disease to the same extent as direct human immunization [ 64 ].…”