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. 2014 Oct 2;8(10):e3122.
doi: 10.1371/journal.pntd.0003122. eCollection 2014 Oct.

Molecular epidemiology of Japanese encephalitis virus in mosquitoes in Taiwan during 2005-2012

Affiliations

Molecular epidemiology of Japanese encephalitis virus in mosquitoes in Taiwan during 2005-2012

Chien-Ling Su et al. PLoS Negl Trop Dis. .

Abstract

Japanese encephalitis (JE) is a mosquito-borne zoonotic disease caused by the Japanese encephalitis virus (JEV). Pigs and water birds are the main amplifying and maintenance hosts of the virus. In this study, we conducted a JEV survey in mosquitoes captured in pig farms and water bird wetland habitats in Taiwan during 2005 to 2012. A total of 102,633 mosquitoes were collected. Culex tritaeniorhynchus was the most common mosquito species found in the pig farms and wetlands. Among the 26 mosquito species collected, 11 tested positive for JEV by RT-PCR, including Cx. tritaeniorhynchus, Cx. annulus, Anopheles sinensis, Armigeres subalbatus, and Cx. fuscocephala. Among those testing positive, Cx. tritaeniorhynchus was the predominant vector species for the transmission of JEV genotypes I and III in Taiwan. The JEV infection rate was significantly higher in the mosquitoes from the pig farms than those from the wetlands. A phylogenetic analysis of the JEV envelope gene sequences isolated from the captured mosquitoes demonstrated that the predominant JEV genotype has shifted from genotype III to genotype I (GI), providing evidence for transmission cycle maintenance and multiple introductions of the GI strains in Taiwan during 2008 to 2012. This study demonstrates the intense JEV transmission activity in Taiwan, highlights the importance of JE vaccination for controlling the epidemic, and provides valuable information for the assessment of the vaccine's efficacy.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Map showing mosquito collection sites in northern, central, southern and eastern Taiwan.
Mosquitoes collected from pig farms and wetlands are indicated with a triangle (▴) and star (★), respectively.
Figure 2
Figure 2. Japanese encephalitis epidemic season in humans and MLE of the JEV infection rates in mosquitoes by month during 2005–2012.
Figure 3
Figure 3. Proportions of genotype distributions of Japanese encephalitis virus strains and annual numbers of Japanese encephalitis cases in Taiwan between 2005 and 2012.
The proportions of genotype distributions in northern (A), central (B), southern (C), eastern (D), all (E) of Taiwan, and the annual numbers of confirmed and death cases of individuals with Japanese encephalitis (F). NA = not available.
Figure 4
Figure 4. Phylogenetic analysis of Japanese encephalitis virus.
The phylogenetic tree shows the genetic relationship of genotype I (A) and genotype III (B) of Japanese encephalitis virus isolates. The tree was constructed based on the nucleic acid sequences of complete envelope (E) genes of the JEV strains. The sequences obtained in this study are indicated in boldface. A sequence obtained from a human case is indicated with a triangle (▴). Viruses were identified by using the nomenclature of virus/country/strain/source/year of isolation/GenBank accession number. Numbers in parentheses indicate the number of isolates that showed 100% nucleotide homology. Virus isolates with the same sequences were collected at the same time from the same locations in this study. CH = Changhua County; HL = Hualien County; KH = Kaohsiung City; TC = Taichung City; TN = Tainan City; TP = New Taipei City; TPC = Taipei City; TY = Taoyuan County; YL = Yilan County; M = mosquito pool; P = pig serum; H = human sample. Analysis was performed using MEGA 5 software and the maximum likelihood method based on the general time-reversible model. The reliability of the analysis was calculated using 1,000 bootstrap replications. Bootstrap support values>75 are shown. The scale bar indicates nucleotide substitutions per site.

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