Seroepidemiological Studies on Japanese Encephalitis: A Systematic Review

Abstract

Background Japanese encephalitis (JE) is one of the major mosquito-borne infectious diseases in the Western Pacific region, accounting for 20-30% of mortality cases. The JE virus (JEV) seroprevalence fluctuations indicate that continuous research is important for prevention and control activities. By mapping JEV seroprevalence by age stratification, the population profile for immunity and susceptibility can be identified to aid in vaccination programme planning. Thus, the aim of this study is to determine the trend of age-specific JEV seroprevalence. Method Systematic search was conducted on all studies conducted on JEV seroprevalence between the years 2010 until 2019. The two search engines used were PubMed and Web of Science. Eligible criteria were set and articles were screened according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines. Three investigators cross-checked all articles assigned. Data were extracted into Excel sheet and results were tabulated in tables and graphs accordingly. Result Four studies from four countries (Taiwan, Sri Lanka, South Korea, India) met the eligibility criteria. The papers show an increasing trend of JEV seropositivity in all countries as their populations reach older age cohorts. Nonetheless, there were slight downtrend notches seen among young adults in Taiwan and India before increasing again after reaching more mature ages. South Korea has the highest seroprevalence rate (97.8% to 98.3%) among the compared countries; this is most likely because it was the earliest to introduce the JEV vaccine in 1967 which was later made mandatory in early 1980s, while India has the lowest seroprevalence rate (12.9% to 18.1%). Among the old-vaccination-naïve population, seropositivity is commonly derived from natural infection. Conclusion Decreases in reported JE cases are mainly due to immunisation. As JEV is expected to remain in nature and the zoonotic chains, the risk of infection will persist. Hence, it is important to apply JEV vaccination protocols in national immunisation programmes with priority given to those at the young childhood stages.