Differential replication efficiencies between Japanese encephalitis virus genotype I and III in avian cultured cells and young domestic ducklings.

Changguang Xiao,Jianchao Wei,Jinpeng Xu,Lihong Liu,Xin Wang,Donghua Shao,Julien Cappelle,Weijie Ren,Zhiyong Ma,Chenxi Li,Xiaodong Wu,Frederik Widén,Beibei Li,Ke Liu,Yafeng Qiu,Di Di,Véronique Chevalier,Linlin Pang

doi:10.1371/journal.pntd.0007046

Abstract

Japanese encephalitis virus (JEV) genotype dominance has shifted to genotype I (GI) from genotype III (GIII) in China as demonstrated by molecular epidemiological surveillance. In this study, we performed a serological survey in JEV-non-vaccinated pigs to confirm JEV genotype shift at the sero-epidemiological level. The average ratio of GI/GIII infection was 1.87, suggesting co-circulation of GI and GIII infections with GI infection being more prevalent in pigs in China. To gain an insight into the reasons for this JEV genotype shift, the replication kinetics of seven recently-isolated JEV isolates including three GI strains and four GIII strains were compared in mosquito C6/36 cells, chicken fibroblast cells (DF-1) and porcine iliac artery endothelial cells (PIEC). We observed that GI strains replicated more efficiently than GIII strains in DF-1 and PIEC cells, particularly in DF-1 cells with titers reaching 22.9–225.3 fold higher than GIII strains. This shows an enhanced replication efficiency of GI viruses in avian cells. To examine this enhanced replication efficiency in vivo, young domestic ducklings were used as the animal model and inoculated with GI and GIII strains at day 2 post-hatching. We observed that GI-inoculated ducklings developed higher viremia titers and displayed a comparatively longer viremic duration than GIII-inoculated ducklings. These results conform to the hypothesis of an enhanced replication efficiency for GI viruses in birds. There are 36 amino acid differences between GI and GIII viruses, some of which may be responsible for the enhanced replication efficiency of GI viruses in birds. Based on these findings, we speculated that the enhanced replication of GI viruses in birds would have resulted in higher exposure and therefore infection in mosquitoes, which could result in an increased transmission efficiency of GI viruses in the birds-mosquitoes-birds enzootic transmission cycle, thereby contributing to JEV genotype shift.

Highlights

Japanese encephalitis virus (JEV) is a zoonotic flavivirus that causes encephalitis in humans and reproductive disorders in pigs in the Asian pacific region [1,2]
The enzootic transmission cycle of JEV is maintained in nature by several species of mosquitoes and vertebrates including birds and pigs
We observed that genotype I (GI) viruses show higher replication titers in avian cells and higher viremia levels in young domestic ducklings than genotype III (GIII) viruses, suggesting an enhanced replication efficiency of GI viruses in birds

Summary

Introduction

Japanese encephalitis virus (JEV) is a zoonotic flavivirus that causes encephalitis in humans and reproductive disorders in pigs in the Asian pacific region [1,2]. The JEV enzootic transmission cycle is maintained in nature by several species of mosquito vectors and vertebrate hosts. Mosquitoes transmit JEV from a viremic vertebrate to a susceptible vertebrate including humans, birds, pigs and other mammals by bite. After infection by JEV-infected mosquitoes, many domestic and wild bird species demonstrate varying degrees of viremia. Some of which, including young domestic ducklings and chicks, as well as ardeid wading birds develop a level of viremia sufficient to infect mosquitoes and are considered the amplifying hosts for JEV transmission [4,5,6]. Among mammal species susceptible to JEV infection, pigs are the only mammals responsible for JEV transmission, because JEV-infected pigs develop a level of viremia that remains high enough to infect mosquitoes for up to 4 days [4]

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