Abstract
Japanese encephalitis virus (JEV), a mosquito-borne zoonotic pathogen, is one of the major causes of viral encephalitis. To reduce the impact of Japanese encephalitis among children in the Republic of Korea (ROK), the government established a mandatory vaccination program in 1967. Through the efforts of this program only 0–7 (mean 2.1) cases of Japanese encephalitis were reported annually in the ROK during the period of 1984–2009. However, in 2010 there was an outbreak of 26 confirmed cases of Japanese encephalitis, including 7 deaths. This represented a >12-fold increase in the number of confirmed cases of Japanese encephalitis in the ROK as compared to the mean number reported over the last 26 years and a 3.7-fold increase over the highest annual number of cases during this same period (7 cases). Surveillance of adult mosquitoes was conducted during the 2010 outbreak of Japanese encephalitis in the ROK. A total of 6,328 culicine mosquitoes belonging to 12 species from 5 genera were collected at 6 survey sites from June through October 2010 and assayed by reverse-transcription polymerase chain reaction (RT-PCR) for the presence of JEV. A total of 34/371 pooled samples tested positive for JEV (29/121 Culex tritaeniorhynchus, 4/64 Cx. pipiens, and 1/26 Cx. bitaeniorhynchus) as confirmed by sequencing of the pre-membrane and envelope protein coding genes. The maximum likelihood estimates of JEV positive individuals per 1,000 culicine vectors for Cx. tritaeniorhynchus, Cx. pipiens, and Cx. bitaeniorhynchus were 11.8, 5.6, and 2.8, respectively. Sequences of the JEV pre-membrane and envelope protein coding genes amplified from the culicine mosquitoes by RT-PCR were compared with those of JEV genotypes I-V. Phylogenetic analyses support the detection of a single genotype (I) among samples collected from the ROK in 2010.
Highlights
Japanese encephalitis virus (JEV), the prototype member of the JEV serocomplex within the genus Flavivirus, family Flaviviridae, is a single stranded positive sense RNA virus
JEV vector surveillance provides information regarding the distribution, intensity, and abundance of circulating viruses that can be used for the development and implementation of disease mitigation strategies by public health officials
Outbreaks/epidemics continued to be reported in India, China, and other countries that did not have comprehensive JEV vaccination programs
Summary
Japanese encephalitis virus (JEV), the prototype member of the JEV serocomplex within the genus Flavivirus, family Flaviviridae, is a single stranded positive sense RNA virus. An estimated three billion persons live in JEV-endemic countries [5], and the annual incidence of Japanese encephalitis (JE) is 30,000– 50,000 cases [6]. Humans and other non-avian vertebrates (e.g., horses) are only infected with JEV incidentally and are considered ‘‘dead-end hosts’’ because they usually fail to produce viremia of sufficient titer to infect mosquitoes. The prototype JEV strain was isolated in Japan in 1935 [8], and the virus has since been found throughout east and southeast Asia, with the geographical borders of viral activity extending north to maritime Siberia [9], west to Pakistan [10], southeast to Australia [11], and northeast to Japan and the Korean
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