Japanese encephalitis (JE) is one of the most important endemic encephalitis in the
world especially in Eastern and Southeastern Asia. JE affects over 50,000 patients
and results in 15,000 deaths annually. JE virus is a single stranded positive sense
RNA virus belonging to family flaviviridae. JE virus is transmitted through a zoonotic
cycle between mosquitoes, pigs and water birds. Humans are accidentally infected and
are a dead end host because of low level and transient viremia. In the northern region,
large epidemics occur during summers whereas in the southern region JE tends to be
endemic: cases occur throughout the year with a peak in the rainy season. Occurrence
of JE is more closely related to temperature than to humidity. JE is regarded as a
disease of children in the endemic areas but in the newly invaded areas, it affects
both the adults and children because of the absence of protective antibodies. For
every patient of JE, there are large numbers of subclinical cases (25-1000). Symptomatic
JEV infection manifests with nonspecific febrile illness, aseptic meningitis or encephalitis.
Encephalitis manifests with altered sensorium, seizures and focal neurological deficit.
Acute flaccid paralysis may occur due to anterior horn cell involvement. A wide variety
of movement disorders especially transient Parkinsonian features and dystonia (limb,
axial, orofacial) are reported in 20-60% patients. JE mainly affects thalamus, corpus
striatum, brainstem and spinal cord as revealed by MRI and on autopsy studies. Coinfection
of JE and cysticercosis occurs because of the important role of pigs in the life cycle
of both JEV and cysticercosis. Laboratory diagnosis of JE is by IgM capture ELISA,
which has high sensitivity and specificity. In the absence of specific antiviral therapy,
JE is managed by symptomatic and supportive therapies and preventive measures. Purified
formalin inactivated mouse brain derived vaccine and live attenuated vaccine (SA 14-14-2)
are available; the latter is reported to be safe, effective and cheap. The role of
Chimeric recombinant attenuated JE vaccine is under investigation. Control of JE is
related to the wider issues of hygiene, environment, education and economy.
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