Japanese Encephalitis Information for Travelers
Date Last Rev'd: July 12, 1996
DESCRIPTION
Japanese encephalitis is a mosquito-borne viral disease that occurs
chiefly in three areas: (1)
China and Korea, (2) the Indian sub-continent consisting of India, parts
of Bangladesh,
southern Nepal, and Sri Lanka, and (3) the southeast Asian countries of
Burma, Thailand,
Cambodia, Laos, Vietnam, Malaysia, Indonesia and the Philippines. Japanese
encephalitis
also may occur with a lower frequency in Japan, Taiwan, Singapore, Hong
Kong, and
eastern Russia. In all areas, Japanese encephalitis is primarily a rural
disease.
Transmission is usually seasonal, following the prevalence of mosquitoes.
In China, Korea
and other temperate areas, the transmission season extends through the
summer and fall. In
other subtropical and tropical regions, risk is associated with the rainy
season, which varies in
each country. For instance, recent epidemics have occurred in northern
India, Nepal, and Sri
Lanka, from October to December. However, in tropical areas, sporadic
cases may occur at
any time of the year.
The chance that a traveler to Asia will develop Japanese encephalitis is
probably very small.
Only 5 cases among Americans traveling or working in Asia are known to
have occurred
since 1981. Only certain mosquito species are capable of transmitting
Japanese encephalitis.
In areas infested with mosquitoes, usually, only a small portion of the
mosquitoes are actually
infected with Japanese encephalitis virus. Among persons who are infected
by a mosquito
bite, only 1 in 50 to 1 in 1000 persons will develop an illness.
The majority of infected persons develop mild symptoms or no symptoms at
all. However,
among persons who develop encephalitis, the consequences of the illness
may be grave.
Japanese encephalitis begins clinically as a flu-like illness with
headache, fever, and often
gastrointestinal symptoms. Confusion and disturbances in behavior also may
occur at an
early stage. The illness may progress to a serious infection of the brain
i.e. encephalitis, and
in one third of cases, the illness may be fatal. Another one third of
cases survive with serious
neurologic after effects such as paralysis or other forms of brain damage,
and the remaining
one third of cases recover without further problems. After the onset of
the infection, and
until the illness has run its course, only supportive treatment is
available. Infection in pregnant
women during the first and second trimester have been associated with
miscarriages.
JAPANESE ENCEPHALITIS VACCINE
The vaccine for Japanese encephalitis is currently available in the United
States through
most traveler's clinics. Travelers to Asia may receive the vaccine, but
CDC recommends the
vaccine only to those who work or have extensive visits during the
transmission season to
rural areas of the previously mentioned countries. The vaccine is
recommended only for
persons who will travel in rural areas for four weeks or more, except
under special
circumstances such as a known outbreak of Japanese encephalitis.
Risk of acquiring Japanese encephalitis is proportional to exposure to the
mosquitos that
breed chiefly in rural rice-growing and pig farming regions. Therefore,
risk is low among the
vast majority of persons whose itineraries are limited to cities or who
will travel to the
countryside only for short periods. These travelers do not require the
vaccine. Older persons
(> 55 years old) may be at higher risk for disease after infection and
should be carefully
considered for vaccination if they travel in areas of risk.
The vaccine is given in 3 doses on days, 0, 7, and 30 and protection can
be expected 10 days
following the last dose. A short course of vaccine can be given on days 0,
7 and 14, but this
vaccination schedule is less effective than the longer course. Serious
allergic side effects
from the vaccine have been reported from up to 0.1% of vaccinees. These
side effects can
be delayed for several days after vaccination and consist of hives and
dangerous swelling of
the throat and mouth. Persons who have multiple allergies, especially to
bee stings and
various drugs, appear to be at higher risk for side effects and probably
should not be
vaccinated except under strict medical supervision. Close medical
supervision should be
available for persons receiving the vaccine for at least 48 hours after
vaccination.
Fever and local reactions such as redness, swelling, and pain are reported
in about 10% of
those vaccinated. There is no information on the usefulness of this
vaccine in children under
1 year old. In children and adults above 1 year old, the vaccine appears
to be over 85%
protective against the illness.
A booster dose may be required two years after the primary vaccination if
the traveler is still
at risk for infection.
The vaccine is also available in many Asian countries and travelers
needing the JE vaccine
abroad are advised to contact the local U.S. Embassy or consulate for a
list of reputable
clinics that may have the vaccine. In China, the vaccine may be obtained
at the U.S.
Embassy and consulates in major cities, but only by citizens who will live
in China for an
extended period.
Because of the potential for other mosquito-borne diseases in Asia, all
travelers are advised
to use precautions to avoid mosquito bites. The mosquitoes which transmit
Japanese
encephalitis feed chiefly outdoors during the cooler hours at dusk and at
dawn. Travelers are
advised to minimize outdoor exposure at these times, to wear mosquito
repellents containing
DEET as an active ingredient, and to stay in air-conditioned or
well-screened rooms.
Repellents containing high concentrations of DEET should be used with care
on children,
because of the potential for neurological side effects. Travelers to rural
areas should bring a
portable bednet, which can be obtained at backpacking and army-navy
surplus stores, and
aerosol room insecticides to kill indoor mosquitoes. Permethrin, a
mosquito
repellent/insecticide can be applied to clothing.
Who Should not be Vaccinated
Some people should generally not receive the vaccine. The CDC recommends
that the
vaccine not be administered to the following persons unless the benefit of
the vaccine clearly
outweighs the risk:
Persons with a history of multiple allergies or hypersensitivity to
components of the
vaccine.
Pregnant women unless there is a high risk of Japanese encephalitis
during the
woman's stay in Asia.
