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Japanese encephalitis in Hong Kong
K Lam, OTY Tsang, RWH Yung,
KK Lau
Department of Medicine and Geriatrics, Caritas Medical Centre, Shamshuipo,
Hong Kong
OBJECTIVES. To review past and present patterns
of occurrence of Japanese encephalitis in Hong Kong and across Asia.
A better understanding of the disease should facilitate the formulation
of an effective strategic plan to prevent a future epidemic.
DATA SOURCES. Report of local cases, and literature
search of MEDLINE up to November 2004.
DATA SELECTION. Literature and data related to Japanese
encephalitis.
DATA EXTRACTION. Relevant information and data were
reviewed by the
authors.
DATA SYNTHESIS. Since 16 July 2004, under the ordinance
of Hong Kong, Japanese encephalitis has been a notifiable disease.
In the past, Japanese encephalitis has reached epidemic proportions
in Japan, South Korea, and some areas in China. It has spread globally
and has a worldwide incidence of 35 000 to 50 000 cases per year
with 10 000 deaths. Mortality is about 30% and survivors often suffer
serious long-term morbidity. In 2004, there were five local cases
of Japanese encephalitis in Hong Kong. Subsequent serological surveillance
of serum samples from 1547 local inhabitants revealed that 37 were
positive, ie 2.4% of local inhabitants had been exposed to the Japanese
encephalitis virus in the past. Most local inhabitants are immunologically
naive to Japanese encephalitis virus.
Most infections in endemic areas are asymptomatic. Patients with
symptomatic Japanese encephalitis usually present with fever, headache,
and confusion. Other signs include neurosis, poliomyelitis, and
convulsion. Investigations including magnetic resonance imaging,
electroencephalography, and single photon emission computed tomography
are not specific. A definitive diagnosis depends on serological
studies. Treatment is mainly supportive.
CONCLUSIONS. The control of Japanese encephalitis
in Hong Kong relies on an accurate surveillance system, vector control,
vector avoidance, and vaccination of the at-risk population. At
present, vaccination should be limited to travellers to endemic
areas who would stay for longer than 1 month.
Hong Kong Med J 2005;11:182-8
Key words: Asia, Southeastern; Encephalitis, Japanese;
Epidemiology; Hong Kong
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