Molecular Detection and Genotyping of Japanese Encephalitis Virus in Mosquitoes during a 2010 Outbreak in the Republic of Korea

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.

In vitro growth, pathogenicity and serological characteristics of the Japanese encephalitis virus genotype V Muar strain

“…Continuous and careful monitoring of the spread of GV viruses must be undertaken. In South Korea, 26 JE patients were reported in 2010, representing a 12-fold increase compared with the mean number that was reported over the previous 26 years (Seo et al, 2013). The relationship between the increase in the number of JE patients in South Korea in 2010 and the emergence of GV JEV remains unknown.…”

Seroconversion to Japanese Encephalitis Virus Among U.S. Infantry Forces in Korea

“…2,3 However, even with these measures in place, JEV remains present in the mosquito populations, through zoonotic transmission, as indicated by outbreaks from 2010 to 2014 (89 cases, 18 deaths) (T. A. Klein, pers. comm.…”

“…For this reason, the ROK government initiated a mandatory childhood National Immunization Program in 1967 that became fully established by 1983, when only 139 cases (12 deaths) were reported. 2,3 From 1984 to 2009, there were only 0-7 cases reported annually as a result of the mandatory childhood vaccination policy. 2,3 However, even with these measures in place, JEV remains present in the mosquito populations, through zoonotic transmission, as indicated by outbreaks from 2010 to 2014 (89 cases, 18 deaths) (T. A. Klein, pers.…”

“…comm.). 2,4 The continued presence of JEV in the ROK poses a potential threat to the greater than 29,000 U.S. Forces military personnel deployed and greater than 13,000 beneficiaries (civilians and family members) who currently reside in the ROK.…”

“…16 Mosquito surveillance in the ROK continues to identify infected pools, highlighting the potential risk of JEV to unvaccinated service members. 4,12,17 In addition, a similar serosurvey of JEV exposure in infantry service members in the ROK before 2006 found approximately 4% of post-deployment specimens positive for JEV antibody using the less specific enzyme-linked immunosorbant assay (R. Schoepp, pers. comm.…”