Characterization of Japanese encephalitis virus (JEV) genotype III clinical isolates in northeast India.

BACKGROUND: Japanese encephalitis virus (JEV) is one of the major etiological agents responsible for causing large numbers of acute encephalitis syndrome (AES) cases in the northeastern region of India. This study was carried out to establish and characterize the circulating strain of JEV in the region in order to understand the disease epidemiology. METHODS: Virus isolation was attempted from 121 patients that presented with AES. Phylogenetic analysis was done using the Kimura-2-Parameter model based on envelope and pre-membrane gene sequence. A pathogenecity study was done in the Swiss albino mice model and assessed by Kaplan-Meier survival analysis. RESULTS: The phylogenetic analysis of the two JEV isolates obtained placed them within genotype (G)III, where they form a subclade within the Vellore group of Indian JEV strains. Neutralization assays suggested similarity between the study isolates and prototype Vellore JEV strain P20778. Pathogenesis in mice suggested that the circulating GIII JEV strains were neuroinvasive. CONCLUSIONS: This study showed that a pathogenic GIII JEV strain was circulating in the northeastern region of India. This finding is important as it is contrary to the belief that GI is gradually replacing GIII as the dominant genotype in Asia. GenBank accession numbers: HQ270470, JQ434468, HQ246155, JX018170.