When Japanese Encephalitis Virus Invaded Eastern Hemisphere – The History of the Spread of Virus Genotypes

Abstract

1.1 Japanese Encephalitis expansion Japanese Encephalitis (JE) was first clinically identified in 1871 in Japan and known as “summer encephalitis”. In 1924, during an outbreak of encephalitis, important studies were carried out at the Tokyo Research Institute of Infectious Disease (Mackenzie et al., 2007). Subsequently, a virus was isolated of a brain of a patient deceased of Japanese summer encephalitis and named “Japanese encephalitis type B” (JEB) in order to distinguish it, by that time, from another intensively circulating pandemic encephalitis, the “von Economo encephalitis”, initially named “Encephalitis Lethargica” (von Economo, 1931), and named afterward “type A encephalitis”. Then, in 1933, the virus responsible of JEB was reisolated and ultimately characterized in 1934, when it was experimentally inoculated into monkey brain and successfully reproduced the disease (Rosen, 1986; Showa in Seiichi & Teizo, 20021; Hayashi, in Asim A. Jani, 20092). From Japan, until the late 1990s, Japanese encephalitis virus (JEV) was known to actively circulate in South East Asia, extending its eastern range towards Korea, Chinese mainland, Taiwan and Philippines, and then further West towards India and Pakistan. Major epidemics occurred in the 1960s and JE appeared endemic within the Indochinese Peninsula including Cambodia, Laos, Thailand and Vietnam, and further on to Malaysia, Burma, Singapore (rare cases), Brunei (Erlanger et al., 2009). Then, within the following four decades, JE occupied subsequently most of the Asian continent from Pakistan to Sri Lanka on the east of its range (Igarashi et al., 1994; Solomon et al., 2000; Nga et al., 2004; van den Hurk et al., 2009) and then Bangladesh, Nepal (Terai region). Furthermore, in the mean time, JEV emerged among unaffected area of Asia as in Papua New Guinea, Far East Russia (maritime Siberia), and subsequently crossed the Torres Strait toward Northern Australia where it was isolated and emerged for the first time within the Australian continent (Hanna