Isolation and identification of a duck-derived Japanese encephalitis virus and evaluation of its virulence in mice.

Birds including domestic and wild birds, as the amplifying or reservoir hosts of JEV, were sensitive to JEV infection and could develop a sufficiently high viremia to infect mosquitoes. However, most of JEV positive reports in birds were based on molecular detection, with few viruses isolated from clinical cases. In this study, one JEV strain, designated duck/2022-SD-1, was first isolated and identified from blood samples of ducks in 2022 in Shandong province of China. The JEV duck/2022-SD-1 strain was classified into genotype I cluster and shared 96.5 to 99.5 % nucleotide sequence identity with other GI JEV strains. Biological characteristics revealed that duck/2022-SD-1 possessed similar replication ability to a virulent strain Beijing/2020-1. Based on the amino acid identity comparison of E protein, amino acid sites responsible for JEV virulence were conserved between duck/2022-SD-1 and other virulence strains. Through virulence assays in mice, we further determined that duck/2022-SD-1 was a highly virulent JEV strain with highly neuroinvasive in mice, which is similar to the virulence of another virulent strain Beijing/2020-1. Thus, the potential threat of JEV strains originating from domestic birds should be brought to people's attention.