Japanese Encephalitis in a U.S. Traveler
Returning from Thailand,
2004 MMWR 11 Feb 2005
Japanese encephalitis (JE) virus is a
mosquito-borne flavivirus that is closely related to the West Nile and St. Louis
encephalitis viruses endemic to North America. JE virus is a leading cause of
viral encephalitis in Asia (1) but is rarely reported among travelers to
countries where JE is endemic (2).
This report describes a case of an unvaccinated Washington resident who had JE
after traveling to northern Thailand. The Advisory Committee on Immunization
Practices (ACIP) recommends JE vaccine for travelers to JE-endemic areas of Asia
during the transmission season, especially those spending >1 month in
those areas and whose travel itineraries include rural settings (2).
JE vaccine should also be considered for travelers visiting areas with epidemic
transmission or those engaging in extensive outdoor activity in rural settings
in areas where JE is endemic, regardless of the duration of their visit. In
addition, health-care providers and organized international travel programs
should ensure that travelers obtain appropriate preventive health guidance
before travel.
Case Report:
In late June 2004, a previously healthy woman
aged 22 years was admitted to a Seattle hospital within hours of returning from
a 32-day visit to Thailand. She had become ill 2 days earlier with fever (101.5ºF
[38.6ºC]), nausea, headache, photophobia, and stiff neck that had
worsened over time. A lumbar puncture was performed; her cerebrospinal fluid (CSF)
revealed a white blood cell count of 47 cells/µL (97% polymorphonuclear
leukocytes), glucose 60 mg/dL, and protein 37 mg/dL. The patient was
presumptively treated for herpes encephalitis with acyclovir and for cerebral
malaria with quinidine and corticosteroids.
Two days later, the patient had dysarthria,
dysphagia, profound lethargy, and fever (104.0ºF [40.0ºC]);
as a result, she was sedated and endotracheally intubated. A nonenhanced
magnetic resonance image revealed edema in the hypothalamus. Polymerase chain
reaction studies of CSF for herpes simplex virus and enteroviruses were
negative, and peripheral blood smears were negative for plasmodia. The patient
improved clinically and was extubated after 2 days but had onset of Bell's palsy
on hospital day 11. After 14 days of hospitalization, she was discharged and
underwent outpatient rehabilitation for 6 weeks. The patient had no apparent
neurologic sequelae. CSF and serum collected 4 days after illness onset and
serum collected 21 days after illness onset had JE virus--specific IgM
antibodies and neutralizing antibodies confirming a recent JE viral infection.
In May 2004, the patient had traveled with 21
other students to Chiang Mai City, Thailand, on a university-affiliated
study-abroad program. Although the program did not require students to consult a
health-care provider before travel, the patient consulted her primary-care
physician. She did not receive any vaccinations or malaria prophylaxis. During
her month-long stay, the patient slept in a dormitory, where her room did not
have screened windows or bed nets. She also spent one night in a poorly screened
cabin in the rural Chiang Mai Valley. The patient reported receiving mosquito
bites in both the dormitory and cabin.
Cohort Survey:
Approximately 6 weeks after
hospital admission, a telephone survey of the patient's travel cohort was
performed. Of 22 students, 20 (91%) participated in the survey; none had a
similar illness. Mean age of respondents was 22 years (range: 19--30 years), and
the median time spent in Asia during the study-abroad program was 6.5 weeks
(range: 4.5--16.0 weeks). In preparation for the trip, five (25%) students
consulted a travel medicine specialist, seven (35%) consulted a primary-care
provider or a parent in the health-care field, and eight (40%) did not consult a
health-care provider. One student was vaccinated against JE. All students
participated in outdoor activities in Thailand, and 19 (95%) reported receiving
mosquito bites. Three (15%) students reported having screens or bed nets at the
dormitory; however, 15 (75%) reported "sometimes" or "always" using insect
repellent while in Chiang Mai City.
On the basis of the cohort survey results,
the Washington State Department of Health recommended that the university
study-abroad program 1) require all students traveling to areas outside of North
America or Western Europe to consult a knowledgeable health-care provider for
advice on appropriate vaccinations, malaria prophylaxis, and other health
precautions before travel, and 2) develop a formal curriculum on travelers'
health topics to be presented during predeparture orientation.
Reported by:
P Hashisaki, MD, Overlake Hospital Medical Center, Bellevue; V Hsu, MD, M
Grandjean, C DeBolt, MPH, J
Duchin, MD, Public Health-Seattle and King County, Seattle; L Kidoguchi, MPH, M
Leslie, DVM, J Hofmann, MD, Washington State Dept of Health. A Marfin, MD, G
Campbell, MD, Div of Vector-Borne Infectious Diseases, National Center for
Infectious Diseases, CDC.
Editorial Note:
JE virus is a leading cause
of viral encephalitis in Asia; JE has a case-fatality rate of approximately 30%
(1,3). No virus-specific treatment exists, and survivors commonly have
neurologic sequelae (1,3). Although JE is a substantial public health
problem in Asian countries, transmission to short-term travelers to JE-endemic
countries rarely has been reported (2,4).
This report describes the first reported case in a U.S. traveler since 1992.
Less than 1% of JE virus--infected persons
have onset of encephalitis (3); however, because an effective JE vaccine
is available, vaccination should be considered for use in travelers to Asia.
Although the risk for infection among travelers is low overall, risk varies
substantially by season (e.g., risk is highest in the rainy season), geographic
location, duration of travel, outbreak presence, and activities of the traveler
(2,5).
Risk estimates based on JE incidence among residents of countries where the
disease is endemic are often inaccurate because JE surveillance is not conducted
in many Asian countries. In countries with childhood vaccination programs or
where the majority of persons aged <15 years have developed immunity after a
natural, asymptomatic JE viral infection, the low incidence among residents can
be misleading. Despite a history of JE outbreaks in rural Chiang Mai Valley (6,7)
and >1 month's stay for all 22 travelers described in this report, 40%
received no pre-travel medical advice from a health-care provider, and only one
was vaccinated against JE.
The specific ecologic setting in which the
patient described in this report was infected is unknown. Swine production and
flood-irrigated rice farming provide a hospitable environment for both the
proliferation of the principal mosquito vector, Culex tritaeniorhynchus,
and amplification of JE virus in swine. Mosquito infection rates can be as high
as 10% in areas where virus transmission to vertebrates is high (8). The
virus can also be transmitted in urban and other ecologic settings, although the
intensity of transmission is often much less than in endemic, rice-producing
areas. JE cases have been reported among urban residents and travelers to Asian
cities who had little or no rural exposure and were likely infected by urban
Culex species (2).
In addition, because wading birds (e.g., egrets) and large mammals other than
swine can serve as amplifying hosts, JE virus transmission can occur in areas
where swine are not raised. JE virus--infected persons do not have high-titer
viremia and are therefore considered "dead-end" hosts.
A single, formalin-inactivated, mouse
brain--derived, JE vaccine is licensed for use in the United States in persons
aged >1 year. The preferred primary vaccination series consists of 3
doses administered at 0, 7, and 30 days, but an accelerated schedule consisting
of 3 doses administered at 0, 7, and 14 days can be used when the longer
schedule is impractical or inconvenient because of time constraints. With either
schedule, the primary series should be completed at least 10 days before travel
to allow an adequate immune response and monitoring of adverse events (AE) after
vaccination; therefore, JE vaccination should begin at least 24 days before
travel abroad. In addition to a moderate rate of local side effects (2),
rare and more serious neurologic (e.g., encephalitis) and allergic AE (e.g.,
urticaria or angioedema) have been reported (9).
JE vaccine is not recommended for all
travelers to Asia. For each traveler, careful consideration of the potential
risks and benefits of vaccination should be made by a health-care provider
familiar with the person's itinerary, the vaccine, and current CDC
recommendations for its use (2).
In general, vaccine should be offered to persons spending >1 month in JE-endemic
areas during the transmission season, especially if travel will include rural
areas. Under specific circumstances, vaccine should be considered for persons
spending <1 month in JE-endemic areas (e.g., travelers to areas experiencing
epidemic transmission and persons whose activities, such as extensive outdoor
activities in rural areas, place them at high risk for exposure). In all
instances, travelers should be advised to take personal precautions to reduce
exposure to mosquito bites (e.g., avoidance of mosquitoes and use of repellents
and protective clothing).
To determine a traveler's need for
vaccination and prophylaxis, health-care providers and travelers can review
regularly updated CDC travel recommendations for JE, malaria, other vector-borne
diseases, and endemic infectious diseases at
http://www.cdc.gov/travel. In addition, health-care providers can call the
CDC Division of Vector-Borne Infectious Diseases, telephone 970-221-6400, or
Division of Global Migration and Quarantine, telephone 404-498-1600. Finally,
organized international travel programs should ensure that their clients obtain
appropriate preventive health guidance before travel.
References
- Halstead SB, Tsai TF. Japanese encephalitis vaccines.
In: Plotkin SA, Orenstein WA, eds. Vaccines. 4th ed. Philadelphia, PA: WB
Saunders; 2004:919--58.
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CDC. Inactivated Japanese encephalitis virus vaccine. Recommendations of the
Advisory Committee on Immunization Practices (ACIP). MMWR 1993;42(No.
RR-1):1--15.
- Solomon T. Flavivirus encephalitis. N Engl J Med
2004;351:370--80.
- Geraghty CM, McCarthy JS. Japanese encephalitis vaccine:
is it being sufficiently used in travelers? Med J Aust 2004;181:269--70.
- Shlim DR, Solomon T. Japanese encephalitis vaccine for
travelers: exploring the limits of risk. Clin Infect Dis 2002;35:183--8.
- Grossman RA, Edelman R, Willhight M, et al. Study of
Japanese encephalitis virus in Chiang Mai Valley, Thailand. Am J Epidemiol
1973;98:133--49.
- CDC. Health information for international travel
2003--2004. Atlanta, GA: US Department of Health and Human Services, Public
Health Service; 2003.
- Maeda O, Karaki T, Kuroda A, et al. Epidemiological
studies on Japanese encephalitis in Kyoto City area, Japan. III. Seasonal
prevalence of virus infections in several pig populations shown by virus
recovery from engorged Culex tritaeniorhynchus summorosus. Jpn J Med
Sci Biol 1978;31:277--90.
- Plesner AM. Allergic reactions to Japanese encephalitis
vaccine. Immunol Allergy Clin North Am 2003;23:665--97.
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