Japanese Encephalitis
- 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.
