Genotype 5 Japanese Encephalitis Virus—Old Genotype, New Threat

Abstract

Japanese encephalitis (JE) is an important viral encephalitis with epidemic status in Asia, which is caused by Japanese encephalitis virus (JEV), a member of the genus Flavivirus. JEV is divided into five genotypes. Genotype 5 (G5) is relatively neglected because of the limited number of cases and strains isolated. The first strain of G5 JEV (Muar strain) was isolated in Singapore in 1952 in a patient from Muar, Malaysia. The second strain (XZ0934) was isolated 57 years later in China, thus indicating the re-emergence of G5 JEV. A female patient who had been vaccinated against JE was infected with G5 JEV in Korea in 2015. JE is a vaccine-preventable disease, and its incidence has decreased with vaccination in many Asian countries. G3 JEV is the main candidate for current JE vaccines, which include attenuated, inactivated and chimeric type vaccines. However, the available vaccines do not provide adequate protection against the older G5 JEV lineage. Therefore, more research on this genotype is crucial for developing better detection methods, expanding surveillance to determine the possible chains of viral transmission for this new threat and developing a polyvalent JEV vaccine.