Japanese Encephalitis

Abstract

Japanese Encephalitis (JE) is an endemic vector-borne (mosquitoes) zoonotic flavivirus disease in Asia with severe neurological manifestations (case fatality rate CFR 20–30%; 30–50% of survivors with serious sequelae). Japanese Encephalitis Virus (JEV) is the leading cause of viral encephalitis in Asia and exposes an estimated 3 billion people to the risk of infection. Other regions of the world have conditions suiting JEV without circulation of the virus (yet). Most JEV infections are asymptomatic or only cause mild symptoms. 1 in 250 infections progresses to severe disease for which no specific treatment is yet available. Neutralizing antibodies develop after infection. In endemic areas this occurs usually during childhood followed by subclinical re-exposure with life-long immunity protecting against disease. Disease in adult populations in endemic areas is rare. General prevention includes avoidance of mosquito bites, e.g., repellents, long-sleeved clothes, coils and vaporizers. Vaccine prevention: Neutralizing antibodies (PRNT50 titer ≥ 1:10) is the correlate of protection. Vaccines currently used are live attenuated JE vaccines and recombinant chimeric JE vaccines (mostly in endemic countries) and cell culture-derived inactivated JE vaccines (travelers, endemic countries). As animal reservoirs of the JEV cannot be eradicated, universal vaccination of humans can control the disease in humans. Optimal JE control in endemic countries is limited by issues around vaccine supply, surveillance (burden of disease underestimation), and resource competition / prioritization.