Japanese Encephalitis Virus

Viruses belonging to the genus Flavivirus of the family Flaviviridae are the established human pathogens and their zoonotic potential has escalated in the last few decades. They are transmitted by vectors and accordingly grouped as tick-borne flaviviruses and mosquito-borne flaviviruses. Viruses transmitted by ticks are closely related species of single sero-complex, whereas mosquito-borne flaviviruses are diverse. Yellow fever virus is the prototype of this genus. There are four important Flaviviruses associated with Japanese encephalitis sero-complex, which causes encephalitis epidemics world over. Examples include Japanese encephalitis, West Nile, Murray Valley encephalitis, and Saint Louis encephalitis viruses. Japanese encephalitis is a leading cause of neurological illness in children’s aged below 15 years. It is transmitted by Culex tritaeniorhynchus mosquito. JEV is maintained in nature by ardeid birds and pigs (both domestic and wild pigs). There are two enzootic cycles of JEV transmission, i.e. pig-mosquito-pig and bird-mosquito-bird cycle. The ardeid birds are the natural reservoir maintaining the JE virus, whereas pigs are the amplifier host. The disease is endemic in South-East Asian countries, and the highest numbers of deaths are recorded in India. JEV is considered as emerging pathogen due to changing epidemiology. JEV is endemic in 24 countries, and most of them are Asian countries. JE is spreading in new area owing to climate change, expansion of vector range, increase in pig husbandry, and population explosion. Introduction of JE vaccines has curtailed down the incidence of JE to a great extent in several endemic countries. India has also recommended JE vaccination for children in the endemic regions. Although immunization of humans is an effective strategy for JEV prevention, its control is challenging due to the existence of different transmission cycles. Especially, risk from the ardeid birds is unpredictable and cannot be controlled. Few countries have attempted JE vaccination in porcine population as a strategy for JE prevention but it is not universally adopted. Co-circulation of different flaviviruses in nature makes the diagnosis and prevention of JE challenging in the endemic countries. In the context of global warming and climate change, it is mandatory to consider JE in One Health paradigm.