Prevalence of Neutralizing Antibodies to Japanese Encephalitis Virus among High-Risk Age Groups in South Korea, 2010

Abstract

After an extensive vaccination policy, Japanese encephalitis (JE) was nearly eliminated since the mid-1980s in South Korea. Vaccination in children shifted the affected age of JE patients from children to adults. However, an abrupt increase in JE cases occurred in 2010, and this trend has continued. The present study aimed to investigate the prevalence of neutralizing antibodies to the JE virus (JEV) among high-risk age groups (≥40 years) in South Korea. A plaque reduction neutralization test was conducted to evaluate the prevalence of neutralizing antibodies to JEV in 945 subjects within four age groups (30–39, 40–49, 50–59, and 60–69 years) in 10 provinces. Of the 945 enrolled subjects, 927 (98.1%) exhibited antibodies against JEV. No significant differences were found in the prevalence of neutralizing antibodies according to sex, age, or occupation. However, there were significant differences in the plaque reduction rate according to age and occupation; oldest age group had a higher reduction rate, and subjects who were employed in agriculture or forestry also had a higher value than the other occupations. We also found that three provinces (Gangwon, Jeonnam, and Gyeongnam) had a relatively lower plaque reduction rate than the other locations. In addition, enzyme-linked immunosorbent assays were conducted to determine recent viral infections and 12 (2.2%) subjects were found to have been recently infected by the virus. In conclusion, the present study clearly indicated that the prevalence of neutralizing antibodies has been maintained at very high levels among adult age groups owing to vaccination or natural infections, or both. In the future, serosurveillance should be conducted periodically using more representative samples to better understand the population-level immunity to JE in South Korea.

Clinical Characteristics of Severe Japanese Encephalitis: A Case Series from South Korea

“…For laboratory diagnosis of JE, all samples from patients were transferred to the KCDC and serological tests were performed as previously described. 12 Anti-JEV IgM antibodies were tested by using the JE-Dengue IgM Combo enzyme-linked immunosorbent assay (ELISA) (Panbio, Australia) and JE Detect IgM ELISA kits (InBios, Seattle, WA) according to the manufacturer's protocols. Anti-JEV IgG antibodies were detected by using the JE Detect IgG ELISA kit (InBios).…”

“…However, the number of JE cases notably increased in 2010, when 26 new cases were confirmed, including seven deaths. 12 This increased JE incidence has continued, reaching a peak of 40 cases in 2015. A total of 129 JE cases were reported between 2010 and 2015, with a case fatality rate of 21.3%.…”

Systematic review of seroepidemiological studies on Japanese encephalitis in the Republic of Korea

“…The first study was conducted by the US military in 1946(Deuel et al, 1950. Following this, four studies were conducted in the 1960s (Lee et al, 1963;Chang et al, 1965;Kim et al, 1965;Chay, 1971), six studies in the 1970s (Kim, 1974;Kim et al, 1976;Lee and Lee, 1976;Lee and Ko, 1979;Lee et al, 1980), two studies in the 1980s (Lee and Youm, 1985;Lee et al, 1989), three studies in the 1990s (Cho et al, 1992;Kim et al, 1996;Choi, 1995), and two studies in the 2010s (Lee et al, 2016;Hong et al, 2013). The timing and seasons of blood sample collection varied across the studies.…”

Japanese encephalitis vaccines: Immunogenicity, protective efficacy, effectiveness, and impact on the burden of disease

“…29 The results on the longevity of responses should be interpreted with caution since the outcome may depend on whether the study was conducted in a non-endemic or an endemic area. Seropositivity rates are known to increase significantly beyond 10-15 years of age in endemic areas, 167,[180][181][182] and an inverse correlation has been observed between an age of >5-6 years and the incidence of JE disease. 167 In addition, direct correlation between seropositivity rates and the incidence of JE in an area has also been documented.…”