The emerged genotype I of Japanese encephalitis virus shows an infectivity similar to genotype III in Culex pipiens mosquitoes from China

Abstract

Japanese Encephalitis virus (JEV) is a zoonotic flavivirus that represents the most significant etiology of childhood viral neurological infections throughout the Asia. During the last 20 years, JEV genotype dominance has shifted from genotype III (GIII) to genotype I (GI). To date, the exact mechanism of this displacement is still not known. Culex (Cx.) mosquitoes are the most common species in China and play an essential role in maintaining JEV enzootic transmission cycle. In this study, we used Cx. pipiens mosquitoes from China as an in vivo mosquito model to explore if mosquitoes played a potential role in JEV genotype shift. We exposed female Cx. pipiens mosquitoes orally to either GI or GIII JEV strains. Midgut, whole mosquitoes, secondary organs, and salivary glands of JEV-infected mosquitoes were collected at 7 and 14 days of post infection (dpi) and subjected to measure the infection rate, replication kinetics, dissemination rate and transmission potential of the infected JEV strains in Cx. pipiens mosquitoes by 50% tissue culture infective dose assay. We found that Cx. pipiens mosquito was competent vector for both GI and GIII JEV infection, with similar infection rates and growth kinetics. After the establishment of infection, Cx. pipiens mosquitoes disseminated both JEV genotypes to secondary organs at similar rates of dissemination. A few GI-infected mosquito salivary glands (16.2%) were positive for GI virus, whereas GIII virus was undetectable in GIII-infected mosquito salivary glands at 7 dpi. However, 29.4% (5/17) and 36.3% (8/22) were positive for GI- and GIII-infected mosquito salivary glands at 14 dpi, respectively, showing an increase in JEV positive rate. No statistical difference in the transmission rate between GI- and GIII-infected mosquitoes was detected. Our experiment data demonstrated that GI and GIII viruses have similar infectivity in Cx. pipiens mosquitoes, suggesting that Cx. pipiens mosquitoes from China may not play a critical role in JEV genotype shift. Although the current data were obtained solely from Cx. pipiens mosquitoes, it is likely that the conclusion drawn could be extrapolated to the role of mosquitoes in JEV genotype shift.

Evaluating the competence of the primary vector, Culex tritaeniorhynchus, and the invasive mosquito species, Aedes japonicus japonicus, in transmitting three Japanese encephalitis virus genotypes

“…Differential infectivity and EIP among JEV genotypes have been demonstrated by Cx . quinquefasciatus in North America [ 44 , 45 ], though no differences were seen in Cx . pipiens in China [ 46 ].…”

“…Therefore, although cautious interpretation may need to be applied when using mosquito colonies adapted to laboratory condition instead of wild population due to the possible impact of reduced genetic variability on susceptibility [ 54 , 55 , 56 ], a study has inferred that an established laboratory colony may be a representative model [ 45 ]. That being the case, future studies using semi-field colonies and/or wild populations will still be essential in completely understanding JEV vector competence, and finally elucidating the likelihood of an endemic transmission cycle establishment through an invasive species.…”

Temperate conditions restrict Japanese encephalitis virus infection to the mid-gut and prevents systemic dissemination in Culex pipiens mosquitoes

“…This corroborates experimental findings from other Cx. pipiens populations from the UK, Europe and Asia [29][30][31] . Given that we recorded such a marked increase in infection and dissemination prevalence at 25 °C it is likely that the limiting temperature at which Cx.…”

NS5-V372A and NS5-H386Y variations are responsible for differences in interferon α/β induction and co-contribute to the replication advantage of Japanese encephalitis virus genotype I over genotype III in ducklings

“…Although mosquitoes are not considered to play a major role in the JEV genotype shift [22,23,32], we measured the replication levels of the GI and GIII strains in a mosquito-derived cell line (C6/36) and observed no significant differences in viral replication between the GI and GIII strains, as monitored by TCID 50 assays (…”