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Essentials of Diagnosis
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Most important vaccine-preventable cause of encephalitis in the Asia-Pacific region
The virus is transmitted by mosquitoes, especially Culex species
Wide symptom spectrum; most infections asymptomatic
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General Considerations
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Most common cause of encephalitis in East Asia with over 68,000 estimated cases and up to 20,400 deaths each year
Most cases occur in the summer and late fall although in tropical and subtropical areas transmission occurs throughout the year
Major outbreaks every 2–15 years often correlate with patterns of agricultural development
Virus is transmitted by mosquitoes, especially Culex species
Wading birds and pigs more commonly sustain the infection as reservoirs; viremia in humans is transient and not usually high enough to sustain transmission
In endemic countries, Japanese encephalitis is primarily a disease of children
Travelers to major urban areas for < 1 month are at minimal risk
Transmission by blood transfusion is documented
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Differential Diagnosis
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St Louis encephalitis
West Nile encephalitis
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Leukocytosis
Mild anemia
Hyponatremia
Cerebrospinal fluid typically shows
Enzyme-linked immunosorbent assay (ELISA) for anti-Japanese encephalitis virus IgM performed on cerebrospinal fluid or serum
Definitive diagnosis requires fourfold increase in virus-specific IgG confirmed by plaque reduction neutralization assay
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In severe disease, brain imaging reveals thalamic lesions, with lesions in the hippocampus, midbrain, basal ganglia, and cerebral cortex varying degrees
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Supportive, including antipyretics, analgesics, bedrest, and fluids
Corticosteroids may result in clinical improvement of opsoclonus myoclonus syndrome
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Cognitive, neurologic, and psychiatric complications, including memory and intellectual impairment, occur in as many as 30–50% of survivors and persist at least 1–2 years after acute infection
Opsoclonus myoclonus syndrome and the Kasabach-Merritt phenomenon of consumptive coagulopathy occur rarely
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Use of mosquito repellents
Wearing long sleeves, long pants, and socks
Use of air-conditioned facilities and bed nets are essential means of protection
Eight effective types of vaccine against Japanese encephalitis are available worldwide, including live attenuated and inactivated vaccines
In the United States, formalin-inactivated Vero-cell culture–derived Japanese encephalitis vaccine (IXIARO) is licensed for the prevention of Japanese encephalitis in non-pregnant persons 2 months of age and older