Japanese encephalitis ;
is a potentially
severe viral disease that is spread by
infected mosquitoes in the agricultural
regions of Asia.
It is one of several mosquito-borne virus
diseases that can affect the central
nervous system and cause severe
complications and death.
Japanese encephalitis can be a risk to
travelers to rural areas where the
disease is common.
There
is no specific treatment for
Japanese encephalitis.
A vaccine is licensed for use in travelers
whose itineraries might put them at risk
for Japanese encephalitis. All travelers
should take precautions to avoid
mosquito bites to prevent Japanese
encephalitis and other mosquito-borne
diseases.
What is Japanese encephalitis?
Japanese encephalitis is a disease that is
spread to humans by infected
mosquitoes in Asia. It is one of a group of
mosquito-borne virus diseases that can
affect the central nervous system and
cause severe complications and even
death.
What is the infectious agent that
causes Japanese encephalitis?
Japanese encephalitis is caused by the
Japanese encephalitis virus, an
arbovirus. Arbovirus is short for
arthropod-borne virus. Arboviruses are
a large group of viruses that are spread
by certain invertebrate animals
(arthropods), most commonly blood-
sucking insects. Like most arboviruses,
Japanese encephalitis is spread by
infected mosquitoes.
Where is Japanese encephalitis
found?
Japanese encephalitis is found
throughout rural areas in Asia.
Transmission can also occur near urban
areas in some developing Asian
countries.
Japanese encephalitis is a seasonal
disease that usually occurs in the
summer and fall in the temperate
regions of China, Japan, and Korea. In
other places, disease patterns vary with
rainy seasons and irrigation practices.
How do people get Japanese
encephalitis?
The Japanese encephalitis virus has a
complex life cycle involving domestic
pigs and a specific type of mosquito,
Culex tritaeniorhynchus, that lives in
rural rice-growing and pig-farming
regions. The mosquito breeds in flooded
rice fields, marshes, and standing water
around planted fields. The virus can
infect humans, most domestic animals,
birds, bats, snakes, and frogs. After
infection, the virus invades the central
nervous system, including the brain and
spinal cord.
What are the signs and symptoms
of Japanese encephalitis?
Most infected persons develop mild
symptoms or no symptoms at all. In
people who develop a more severe
disease, Japanese encephalitis usually
starts as a flu-like illness, with fever,
chills, tiredness, headache, nausea, and
vomiting. Confusion and agitation can
also occur in the early stage. The illness
can progress to a serious infection of the
brain (encephalitis) and can be fatal in
30% of cases. Among the survivors,
another 30% will have serous brain
damage, including paralysis.
How soon after exposure do
symptoms appear?
Symptoms usually appear 6-8 days after
the bite of an infected mosquito.
How is Japanese encephalitis
diagnosed?
Diagnosis is based on tests of blood or
spinal fluid.
How common is Japanese
encephalitis?
Japanese encephalitis is the leading
cause of viral encephalitis in Asia, where
30,000 to 50,000 cases are reported
each year. The disease is very rare,
however, in U.S. travelers to Asia.
The chance that a traveler to Asia will
get Japanese encephalitis is very small:
1) only certain mosquito species can
spread Japanese encephalitis; 2) in areas
infested with mosquitoes, only a small
portion of the mosquitoes are usually
infected with Japanese encephalitis
virus; 3) among persons who are
infected by a mosquito bite, only 1 in 50
to 1 in 1,000 will develop an illness. As a
result, fewer than 1 case per year is
reported in U.S. civilians and military
personnel traveling to and living in Asia.
Only 5 cases among Americans traveling
or working in Asia have been reported
since 1981.
Who is at risk for Japanese
encephalitis?
Anyone can get Japanese encephalitis,
but some people are at an increased
risk:
People living in rural areas where the
disease is common
Active-duty military deployed to areas
where the disease is common
Travelers to rural areas where the
disease is common (very small
increased risk)
What is the treatment for Japanese
encephalitis?
There is no specific treatment for
Japanese encephalitis. Antibiotics are not
effective against viruses, and no
effective anti-viral drugs have been
discovered. Care of patients centers on
treatment of symptoms and
complications.
How can Japanese encephalitis be
prevented?
A vaccine is licensed for use in U.S.
travelers to rural areas where the
disease is common. The vaccine is
recommended only for persons who plan
to travel in these areas for 4 weeks or
more, except in special circumstances
such as an ongoing outbreak of disease.
Because of the potential for other
mosquito-borne diseases in Asia, all
travelers should take steps to avoid
mosquito bites. The mosquitoes that
transmit Japanese encephalitis feed
mainly outside during the cooler hours at
dusk and dawn. Travelers should
minimize outdoor activities at these
times, use mosquito repellent on
exposed skin, and stay in air-conditioned
or well-screened rooms. Travelers to
rural areas should use a bednet and
aerosol room insecticides.
This fact sheet is for information only
and is not meant to be used for self-
diagnosis or as a substitute for
consultation with a health-care provider.
If you have any questions about the
disease described above, consult a
health-care provider.
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