Molecular Epidemiology of Japanese Encephalitis Virus in Mosquitoes in Taiwan during 2005–2012

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.

A Japanese Encephalitis Virus Genotype 5 Molecular Clone Is Highly Neuropathogenic in a Mouse Model: Impact of the Structural Protein Region on Virulence

“…From the isolation of the prototype strain of JEV in 1935 until recently, most of the circulating strains of JEV belonged to g3 and were at the origin of major epidemics in Southeast Asian countries (5). Recently, a shift in prevalence from JEV g3 to g1 has been observed in several Asian countries (6)(7)(8), while some strains of JEV g5 have been occasionally isolated in China in 2009 (9) and in South Korea in 2010 (10). The JEV g5 prototype strain, strain Muar, was originally isolated in 1952 from an encephalitis patient in Malaysia (11) and was found to be genetically and serologically distinct from other genotypes (12)(13)(14).…”

Epidemiological Features of Japanese Encephalitis in Taiwan from 2000 to 2014

“…7,19 Another possible reason is that there has been a dramatic shift in the dominant genotype of the JEV from GIII to GI circulating in Taiwan over the past two decades. 15,20,21 It has been found that antibodies elicited by JE-VAX (Nakayama strain) among Taiwanese children show reduced neutralizing potency against the genotype of the emerging GI JEV strain. 22 Taiwan has been using an inactivated mouse brain Nakayama-NIH vaccine strain since 1968, except for the brief use of an inactivated freeze-dried Beijing vaccine strain in 1988.…”

“…These provide suitable environments for maintaining the JEV infection cycle. 16,27 2) In Taiwan, almost all DF cases (approximately > 95%) over the last decade occurred in the southern region of Taiwan. 6,7 This fact and the high proportion of JE cases suggest that mosquitoes and the JE virus are well adapted to this region.…”

“…12,15 Cell culture techniques using a mosquito C6/36 cell line or plaque assays using the BHK-21 cell line were used for virus isolation. 16 Viral RNA was exacted from the JEV-infected culture medium using the QIAamp Viral RNA Mini Kit (Qiagen, Germantown, MD). 16 Statistical analysis.…”

“…16 Viral RNA was exacted from the JEV-infected culture medium using the QIAamp Viral RNA Mini Kit (Qiagen, Germantown, MD). 16 Statistical analysis. The annual incidence rate of JE was calculated by dividing the number of confirmed JE cases by the number of individuals in the total population of the same age as reported in Taiwan's census between 2000 and 2014 and is expressed as the number of JE cases per 1,000,000 people.…”