Genotype Change in Circulating JEV Strains in Fujian Province, China

Distribution and frequency of genetic mutations in three insecticide targets in field populations of Culex tritaeniorhynchus in Mianyang City, Sichuan Province, China

Japanese encephalitis (JE) is an important mosquito borne infectious disease which is mainly transmitted by Culex tritaeniorhynchus Giles (1901) in China. At present, vector control remains an important means to prevent and control vector-borne diseases including JE. The development of insecticide resistance has seriously threatened the effectiveness of insecticide-based vector control programmes. Therefore, understanding insecticide resistance in the target pest is essential to inform evidence-based vector control. In Mianyang City of Sichuan Province of China, Cx. tritaeniorhynchus is the dominant mosquito species, and JE has been documented in this city. Unfortunately, there is little information on the status and underlying mechanisms of insecticide resistance in field populations of Cx. tritaeniorhynchus, the main JE vector in this region. In the study, a total of 314 adults of Cx. tritaeniorhynchus, collected from 6 sites across Mianyang City, were inspected for resistance-conferring mutations in three genes encoding voltage-gated sodium channel (VGSC), Gamma-aminobutyric acid (GABA) receptor Rdl subunit (Rdl), and acetylcholinesterase (AChE) by DNA Sanger sequencing. The results showed that the classical L1014F mutation in VGSC was distributed in all the 6 populations at varying frequencies from 16.98% to 27.78%, and the frequency of F455W mutation in AChE was extremely high (97.06%-100%). Notably, the conserved mutations A296S and V327I previously reported in the Rdl of some other species of mosquitoes were discovered in Cx. tritaeniorhynchus for the first time. The frequency of the resistant Rdl 296S allele was 62.04% to 94.00%, while the V327I mutation was present at a much lower frequency ranging from 0.93% to 1.8%. Overall, the prevalent co-existence of resistance-conferring mutations in multiple insecticide target proteins in Cx. tritaeniorhynchus populations in Mianyang City indicates a worrying status of insecticide resistance, and suggests that it is highly required to monitor the phenotypic resistance of Cx. tritaeniorhynchus on a regular basis.

Genetic Characterization of Japanese Encephalitis Virus Isolates Circulating in Mosquitoes from Pig and Sheep Farms in Shanghai, China

Japanese encephalitis virus (JEV) is regarded as an emerging and reemerging pathogen that is a primary cause of viral encephalitis in humans. However, there is a scarcity of research on the prevalence of JEV genotypes across the different mosquito species in Shanghai. In this study, the diversity of mosquito species and prevalence of JEV in pig and sheep farms in Shanghai were surveyed in 2022. A total of 24,073 mosquitoes, belonging to four genera and seven species, were collected from pig and sheep enclosures in the Chongming, Jiading, Pudong, Fengxian, and Jinshan Districts of Shanghai. Culex tritaeniorhynchus was identified as the predominant species (87.09%, 20,965/24,073) with the highest JEV detection rate. Six strains of JEV were isolated in this study, and genetic analysis revealed that five strains (SH22-M5, SH22-M9, SH22-M14, SH22-M41, and SH22-M52) belonged to genotype I (GI), while one strain (SH22-M1) was classified as genotype III (GIII). The sequence homology was highest between SH22-M9 and SD-1 (99.87%) and between SH22-M14 and SD12 (99.53%). SH22-M5, SH22-M41, and SH22-M52 shared the highest sequence homology with the HEN07011 strain (99.73-99.93%). SH22-M1 was most closely related to SH18, with a sequence homology of 99.8%. Additionally, for the first time, the GI JEV strain was isolated from mosquitoes in sheep sties in this study. The findings highlight the necessity of enhancing the surveillance of JEV in pigs and other livestock farms, including sheep, as well as monitoring the mosquitoes present in these environments. It is recommended that livestock farming areas be kept separate from human habitation to reduce the risk of JEV infections in humans.

Survey of mosquito species in intensive pig farms in Hunan province, China

Mosquitoes (Diptera: Culicidae) are one of the most studied groups of arthropods worldwide due to their high transmission capacity for pathogens, including viruses and parasites. During June to October 2022, the prevalence of mosquito species in 12 intensive pig farms from 12 representative administrative regions in Hunan province of China was investigated using traps with ultraviolet light. All collected mosquitoes were counted and identified to species according to morphological and molecular methods. A total of 4,443 mosquito specimens were collected in the pig farms, and they represented one family, four genera and nine species. Culex pipiens pipiens (24%) was the most common mosquito species, followed by Armigeres subalbatus (23.4%) and Culex tritaeniorhynchus (20.6%). Phylogenetic analyses based on mitochondrial cox1 sequences revealed all mosquito species from present study grouping into distinct monophyletic groups corresponding to nine known mosquito species with strongly supported. The results of the present investigation have implications for the ongoing control of mosquito infestation in pig farms in Hunan province, China. This is the first report of mosquito populations in intensive pig farms in Hunan province, China.

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.