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Health |
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| Japanese
encephalitis (JE), a mosquito-borne flaviviral infection, is the leading
cause of childhood encephalitis in Asia, where up to 50,000 cases may
be reported annually. Most infections are asymptomatic, but when encephalitis
develops, the case-fatality rate can be as high as 30%. Neuropsychiatric
sequelae are reported in 50% of survivors. Although children are at greatest
risk of infection in endemic areas, outdoor
occupation, recreational exposure, and male gender are also risk factors
for infection. |
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Immunity
to JE virus from previous vaccination or naturally acquired immunity reduces
the risk of illness. Although most adults living in endemic areas have
acquired natural immunity and older persons rarely develop illness,
a high case-fatality rate has also been reported in the elderly
JE
virus is transmitted chiefly by mosquitoes in the Culex vishnui complex;
the specific species depends on the geographic area. In China and other
endemic areas in Asia, C. tritaeniorhyncus is the principal vector. This
species feeds outdoors beginning at dusk and during evening hours until
dawn. Larvae are found in flooded rice fields, marshes, and other small
stable collections of water found around cultivated fields. In temperate
zones, this vector is present in greatest density from June
through September; it is inactive during
winter months.
It
has a wide host range that includes domestic mammals, birds, and humans.
Swine and certain species of wading birds are the amplifying hosts in an
enzootic transmission cycle. Because JE virus primarily cycles among
animals and mosquitoes and because national JE vaccination programmes
are present in many affected countries, the absence of human infections
alone should not be used to gauge a traveller's risk for infection.
| The
disease and how it affects people |
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| Japanese
encephalitis (JE) is a disease caused by a flavivirus that affects
the membranes around the brain. Most JE virus infections are mild
(fever and headache) or without apparent
symptoms, but approximately 1 in 200 infections results in severe disease
characterized by rapid onset of high fever,
headache, neck stiffness, disorientation, coma, seizures, spastic paralysis
and death. |
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The
case fatality rate can be as high as 60% among those with disease symptoms;
30% of those who survive suffer from lasting damage to the central nervous
system. In areas where the JE virus is common, encephalitis
occurs mainly in young children because older children and adults have
already been infected and are immune.
An
effective killed vaccine is available for Japanese encephalitis, but it
is expensive and requires one primary vaccination followed by two boosters.
Sources:
BBC and CDC
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