Abstract
BackgroundContinuous vector pathogen surveillance is essential for preventing outbreaks of mosquito-borne diseases. Several mosquito species acting as vectors of Japanese encephalitis virus (JEV), dengue virus, Zika virus, malaria parasites and other pathogens are primary mosquito species in Shanghai, China. However, few surveys of human pathogenic arboviruses in mosquitoes in Shanghai have been reported in the last ten years. Therefore, in this study, we evaluated mosquito activity in Shanghai, China during 2016 and tested for the presence of alphaviruses, flaviviruses, orthobunyaviruses and several parasitic pathogens.ResultsFive pooled samples were JEV-positive [4/255 pools of Culex tritaeniorhynchus and 1/256 pools of Cx. pipiens (s.l.)] based on analysis of the NS5 gene. Alphaviruses, orthobunyaviruses, Plasmodium and filariasis were not found in this study. Phylogenetic and molecular analyses revealed that the JEV strains belonged to genotype I. Moreover, newly detected Shanghai JEV strains were genetically close to previously isolated Shandong strains responsible for transmission during the 2013 Japanese encephalitis (JE) outbreak in Shandong Province, China but were more distantly related to other Shanghai strains detected in the early 2000s. The E proteins of the newly detected Shanghai JEV strains differed from that in the live attenuated vaccine SA14-14-2-derived strain at six amino residues: E130 (Ile→Val), E222 (Ala→Ser), E327 (Ser→Thr), E366 (Arg→Ser/Pro), E393 (Asn→Ser) and E433 (Val→Ile). However, no differences were observed in key amino acid sites related to antigenicity. Minimum JEV infection rates were 1.01 and 0.65 per 1000 Cx. tritaeniorhynchus and Cx. pipiens (s.l.), respectively.ConclusionsFive new Shanghai JEV genotype I strains, detected after a ten-year hiatus in local mosquito surveillance, were genetically close to strains involved in the 2013 Shandong JE outbreak. Because JEV is still circulating, vaccination in children should be extensively and continuously promoted. Moreover, JEV mosquito surveillance programmes should document the genotype variation, intensity and distribution of circulating viruses for use in the development and implementation of disease prevention and control strategies.
Highlights
Continuous vector pathogen surveillance is essential for preventing outbreaks of mosquito-borne diseases
Detection of mosquito-borne pathogens from samples In total, 21,881 adult mosquitoes belonging to nine species from five genera of the family Culicidae (Culex, Aedes, Anopheles, Mansonia and Coquillettidia) were collected at 94 survey sites (Fig. 1) during the peak mosquito activity period from May to November 2016 in Shanghai
Historical co-circulation of Japanese encephalitis virus (JEV) GI and GIII strains in Shanghai The first JEV strain found in Shanghai was isolated from a human brain in 1987 and classified as the GIII genotype [30]
Summary
Continuous vector pathogen surveillance is essential for preventing outbreaks of mosquito-borne diseases. Several mosquito species acting as vectors of Japanese encephalitis virus (JEV), dengue virus, Zika virus, malaria parasites and other pathogens are primary mosquito species in Shanghai, China. Few surveys of human pathogenic arboviruses in mosquitoes in Shanghai have been reported in the last ten years. In this study, we evaluated mosquito activity in Shanghai, China during 2016 and tested for the presence of alphaviruses, flaviviruses, orthobunyaviruses and several parasitic pathogens. Japanese encephalitis virus (JEV) is an arbovirus prevalent throughout Asia and in parts of the western and south Pacific [1, 2]. Rice paddy-breeding Culex tritaeniorhynchus is the primary JEV vector [1]. Pigs, wading birds and bats are susceptible reservoirs and act as amplifiers of JEV [9]. Cows and horses are dead-end hosts [10], as they
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