Virology
The causative agent Japanese encephalitis virus is an enveloped virus of the genus flavivirus and is closely related to the West Nile virus and St. Louis encephalitis virus. The positive sense single stranded RNA genome is packaged in the capsid which is formed by the capsid protein. The outer envelope is formed by envelope (E) protein and is the protective antigen. It aids in entry of the virus to the inside of the cell. The genome also encodes several nonstructural proteins also (NS1,NS2a,NS2b,NS3,N4a,NS4b,NS5). NS1 is produced as secretory form also. NS3 is a putative helicase, and NS5 is the viral polymerase. It has been noted that the Japanese encephalitis virus (JEV) infects the lumen of the endoplasmic reticulum (ER) and rapidly accumulates substantial amounts of viral proteins for the JEV.
Japanese Encephalitis is diagnosed by detection of antibodies in serum and CSF (cerebrospinal fluid) by IgM capture ELISA.
Viral antigen can also be shown in tissues by indirect fluorescent antibody staining.
Based on the envelope gene (E) there are five genotypes (I - V). The Muar strain, isolated from patient in Malaya in 1952, is the prototype strain of genotype V. Genotype IV appears to be the ancestral strain and the virus appears to have evolved in the Indonesian-Malayasian region. The first clinical reports date from 1870 but the virus appears to have evolved in the mid 1500s.
Over 60 complete genomes of this virus have been sequenced as of 2010.
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