JAPANESE ENCEPHALITIS
JE disease: Mosquito-borne viral infection, similar to West Nile virus
which has recently come to the US. The reservoir is pigs in JE (birds in West
Nile). JE is endemic in much of southern Asia in spring, winter and fall, but is
highly season and geography dependent. Infects many in an endemic area, but
seriously affects few. Those who develop brain infection have a significant
death and permanent disability rate.
JE vaccine: Expensive; 3 doses over a month; 1% allergic rate to the
vaccine (hives and throat or lip swelling) with hospitalizations, but no deaths.
You should remain within easy access of medical care for 10 days after each
dose. That means no backpacking, and no airplane flights. JE vaccine is given as
a general childhood vaccine in many Asian countries.
Japanese encephalitis email correspondence among travel
medicine doctors
I have recently been advised of a case of confirmed Japanese encephalitis in
a New Zealand traveler. This 49 year old female was hospitalized in July, 2004,
immediately on return to NZ from a trip of about 5 weeks to Japan, China and
Hong Kong. The patient had not had any travel vaccinations. She traveled first
to Japan (12 days), then China (3 weeks, including some urban stays and a trip
to the Yangtze River for 4 days), and finally Hong Kong (2 days) before
returning to New Zealand. All sleeping accommodations were air conditioned,
except for 2 days of the trip (while traveling on trains in China). No other
mosquito/insect bite precautions were taken; mosquitoes were seen, but no bites
were noticed by the patient.
As the incubation period for Japanese encephalitis is 5-15 days, it is inferred
that the patient acquired the disease in China. The main manifestation of
illness in this case was a severe meningoencephalitis (brain infection) with
permanent thinking impairment and paralysis.
Japanese encephalitis is an unusual disease for travelers to acquire in the
region for such a short time. Of particular note is the fact that there did not
appear to be extended travel into rural areas. Recently there have been two
reports of Japanese encephalitis in nearby Hong Kong, also an unusual
occurrence, emphasizing the need to advise all travelers to Asia fully on the
benefits of preventative vaccination and protection against mosquito bites (and
making this specific to an intended itinerary of travel).
Reply:
This unfortunate case raises an issue which I believe has not been definitively
dealt with, and that is how rigid travel health advisors should be in
extrapolating from epidemiological data when advising individual travelers. This
becomes particularly pertinent when the consequences of contracting a disease
can be catastrophic.
The usual advice that would have been given to the traveler described would have
been that vaccination against Japanese encephalitis would not have been
warranted, yet her lack of vaccination appears to have ruined her life. The
evidence on the cost-effectiveness of meningococcal vaccine in the United States
is that vaccination can never be justified on economic grounds, yet many parents
sending their children to college are willing to pay for the vaccine.
If a traveler faces the risk, albeit very small, of an illness whose outcome may
be death or permanent brain damage, then should the travel health advisor be
concerned with the risk-benefit ratio of the intervention rather than the
cost-benefit ratio?
Further comment:
It happens that the measured risk of getting severe JE in China is less than 1
in a million. It's up to the practitioner and the traveler to decide whether 1
in a million means "there's still a chance." Some would take comfort in those
odds, others would feel it was worth vaccinating against. Few would feel that
1,000,000 travelers should be vaccinated to prevent one case of JE.
Climate changes and increased commerce and travel between locales have made it
increasingly hard to predict appearance of diseases in new locations (for
example, West Nile virus in North America). Whether we should interpret this
fact as a need to be more free with vaccine advice remains to be determined. An
Israeli tourist acquired a severe case of JE in Thailand in 1989. This led
Israeli public health authorities to recommend JE vaccine to all Israeli
travelers to Thailand, even though the vaccine was not available in Israel at
the time. Is this applied common sense and epidemiology, or a reaction to an
anecdotal event? Which is the more valid way to prevent tragedy?
The second issue is the risk of the vaccine. First of all, we need to clarify
the reactions we are concerned about. Hives and swelling of the throat have been
described, but anaphylaxis is almost unheard of. Only three cases of
anaphylactoid reactions appear in the literature, all from a survey in Korea.
Among 10,000,000 doses that were surveyed in Japan and the USA, there was only
one fatality (a 3 year old Japanese child from a neurological reaction). Adverse
neurological reactions appear to be a more serious concern, but their rate of is
about 1 in 50,000 to 1 in 100,000. These figures are soft, because they often
have not been repeated in other surveys. 08/25/2004
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