is Japanese B encephalitis?
Japanese B encephalitis is the leading cause of viral encephalitis in Asia,
with 30-50,000 cases reported annually. It has a fatality ratio of 30% and there
are serious neuralgic (affected by pain in the sensory nerve) consequences in
another 30% of cases.
are the symptoms of Japanese B encephalitis?
The incubation period is usually five to 15 days. The majority of Japanese
B encephalitis infections are subclinical (have no symptoms) and many infected
people become symptomless carriers. Mild infections occur with few apparent
symptoms other than fever with headache.
More severe infection is marked by:
- Quick onset.
- High fever.
- Neck stiffness.
- Occasional convulsions (especially in infants).
- Spastic (occasionally flaccid) paralysis.
Acute encephalitis can progress to paralysis, seizures, coma and death.
is Japanese B encephalitis transmitted?
Rice field breeding mosquitoes (primarily the Culex tritaeniorhynchus group)
become infected by feeding on domestic pigs and wild birds infected with the
Japanese encephalitis virus.
Infected mosquitoes then transmit the Japanese encephalitis virus to humans
and animals by biting them. Only domestic pigs and wild birds are carriers of
the Japanese encephalitis virus.
are the high risk destinations for Japanese B encephalitis infection?
It is found almost exclusively in Asia but there is a growing incidence of
Japanese B encephalitis in Northern Australia. Countries which have had major
epidemics in the past but which have controlled the disease primarily by vaccination
include China, Korea, Japan, Taiwan and Thailand.
Other countries that still have periodic epidemics include Vietnam, Cambodia,
Myanmar, India, Nepal, and Malaysia. Seasonality of the illness varies by country,
for example May to September in Northern China, May to October in Thailand and
Goa; July to December in Northern India; June to September in Japan; April to
October in Southern China; and year round transmission with an April peak in
can infection be prevented?
The only means of infection is the bite of mosquitoes infected with the Japanese
encephalitis virus. Japanese encephalitis virus is NOT transmitted from person-to-person.
For example, you cannot get the virus from touching or kissing a person who
has the disease, or from a healthcare worker who has treated someone with the
is Japanese B encephalitis treated?
There is no specific therapy. Intensive supportive therapy is indicated.
I be vaccinated against Japanese B encephalitis?
Japanese encephalitis vaccine is NOT recommended for all travellers to Asia.
In general, vaccine should be offered to persons spending a month or longer
in endemic areas during the transmission season, especially if travel will include
can I do?
Japanese encephalitis does not usually occur in urban areas and rarely infects
travellers. Residents of rural areas in endemic locations are most at risk.
Risk for most short-term travellers may be one per million. Special factors
should be considered by elderly persons and pregnant women who plan visits to
areas where Japanese encephalitis is endemic. Japanese encephalitis acquired
during pregnancy carries the potential for intrauterine infection and foetal
can I get further information?
Your GP will be able to advise you on the vaccinations
necessary for travel to various regions. Travel vaccination information is also
available at www.cdc.gov/travel/
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