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.
Since the 1980's, several kinds of inactivated bovine viral diarrhea virus (BVDV) vaccines have been used to immunize domestic animals such as cattle and goat in Korea. Immunogenicity of the BVDV vaccines has been checked by the Korean Veterinary Authority using laboratory animals. In this study, we applied a molecular method to investigate the genetic characterization of the BVDV genes in six commercial inactivated BVDV vaccines, and determined the efficiency of two extraction reagents (i.e., sodium citrate or isopropyl myristate) to separate the vaccine antigens from the antigen/adjuvant complexes. Six partial non-coding regions (288 bp) were successfully amplified with specific primer sets, which demonstrated that sodium citrate is more efficient in extracting viral RNA from inactivated gel vaccines than isopropyl myristae. In addition, we identified the virus strains from the vaccines by analyzing the nucleotide sequences of the 5' non-coding region (NCR) of BVDV. The nucleotide similarity of the partial 5' NCR ranged from 95.1 to 100% among BVDV vaccine strains, respectively, indicating that a few manufacturers used different BVDV strains to produce their vaccines.
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