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. 2020 May 26;14(5):e0008312.
doi: 10.1371/journal.pntd.0008312. eCollection 2020 May.

An outbreak of Japanese encephalitis caused by genotype Ib Japanese encephalitis virus in China, 2018: A laboratory and field investigation

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An outbreak of Japanese encephalitis caused by genotype Ib Japanese encephalitis virus in China, 2018: A laboratory and field investigation

Wenjing Liu et al. PLoS Negl Trop Dis. .

Abstract

Although Japanese encephalitis virus genotype Ib (JEV GIb) has replaced JEV GIII as the dominant genotype in endemic areas of Asia, no JEV GIb has been isolated from JE cases and natural mosquitoes at the same time in an outbreak of JE. In this study, we conducted virological and molecular biological laboratory tests on JE case samples (serum/cerebrospinal fluid) and locally collected mosquito samples from the 2018 JE outbreak in Ningxia, China. The result of JEV IgM antibody detection showed that 96% (67/70) of the suspected cases were laboratory-confirmed JE cases. Of the mosquitoes collected from local environments, 70% (17400/24900) were Culex tritaeniorhynchus of which 4.6% (16 /348 of the pools tested) were positive for JEV, other mosquitoes were negative. JEVs isolated from both the human cases and C. tritaeniorhynchus specimens belong to JEV GIb and are in the same evolutionary clade according to molecular evolution analyses. JEV GIb was detected simultaneously from specimens of JE cases and mosquito samples collected in nature in this study, suggesting that the JE outbreak that occurred in Ningxia in 2018 was due to infection of JEV GIb.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Cytopathic effect (CPE) of virus isolate NX1889 in Vero cells.
CPE induced by inoculating CSF specimens from NX1889 cases into Vero cells. Magnification, ×ばつ (×ばつ20). 4 days after inoculation, obvious CPE was observed, which presented as circular shrinkage and shedding of the cell.
Fig 2
Fig 2. Spatiotemporal distribution of the 2018 JE incidence in Ningxia.
The information of JE cases demonstrated on the map were obtained from the National Notifiable Disease Reporting System (NNDRS). The spatiotemporal distribution of JE cases was analyzed using ArcGIS (v.10.0; ESRI, Redlands, CA, USA). Each point represents a case of JE; red points are cases reported (excludes the JE cases diagnosed in this study) in Ningxia in 2018, and blue points are confirmed cases diagnosed in this study. From the south to the north: GY, Guyuan City; ZW, Zhongwei City; WZ, Wuzhong City; YC, Yinchuan City; and SZS, Shizuishan City, same in Fig2(A, B, C). The shading scheme for this map is used to distinguish the five different cities of Ningxia province. Fig2A shows that 1 case was reported in July, Fig2B shows that 113 cases were reported in August, of which 67 were confirmed cases diagnosed in this study, Fig2C shows that 48 cases were reported in September.
Fig 3
Fig 3. Phylogenetic analyses of the E fragment of JEV from human cases and mosquitoes.
Blue indicates JE gene sequences from mosquito specimens of Ningxia in 2018. Red indicates the JEV isolate (NX1889) from cerebrospinal fluid specimens of JE cases. Fig 3A used data set of reported JEV GIb isolates[11] along with JEV GIbs from the 2018 Ningxia outbreak, including seven JEV sequences from mosquitoes and one from human; To visualize the phylogenetic relationship of JEV GIbs from Ningxia, the referenced JEV GIb isolates shown in Fig 3B were selected from Fig 3A and represent different hosts (equid, midge, human, mosquito, pig, and unknown host), different countries (China, Japan, Korea, Korea, Vietnam, Thailand, and Australia), and different times (from the 1970s to 2000s).

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