Other meanings of Japanese encephalitis
INFECTIOUS DISEASE
Japanese encephalitis is a viral brain infection transmitted by mosquitoes, primarily in Asia. It is caused by Japanese encephalitis virus, a flavivirus maintained in cycles involving mosquitoes, pigs, and water birds; most infections produce no symptoms, but severe disease can cause inflammation of the brain, lasting neurological disability, or death.1
Japanese encephalitis is caused by Japanese encephalitis virus, an enveloped, single-stranded RNA flavivirus related to West Nile, dengue, and yellow fever viruses.2 The virus is transmitted mainly by Culex mosquitoes, especially species that breed in rice fields, wetlands, and other areas with standing water. These mosquitoes are most active from dusk to dawn, although exposure patterns vary by species and region.
The natural transmission cycle usually involves mosquitoes feeding on infected pigs or wading birds; humans and horses are incidental, “dead-end” hosts because they generally do not develop enough virus in the blood to infect new mosquitoes.1 Person-to-person spread does not normally occur. Risk is therefore shaped by season, rainfall, irrigation, animal husbandry, land use, and travel to or residence in endemic areas.
Most Japanese encephalitis virus infections are asymptomatic, while a small fraction progresses to encephalitis, the inflammation of brain tissue.1 Early symptoms can include fever, headache, vomiting, weakness, and confusion; severe illness may bring seizures, neck stiffness, movement disorders, impaired consciousness, and paralysis. Children may be particularly vulnerable to severe neurological consequences, though disease can affect people of any age.
Diagnosis relies on clinical assessment and laboratory testing, usually detection of virus-specific immunoglobulin M in cerebrospinal fluid or serum. Other causes of encephalitis must be considered because the symptoms overlap with infections such as herpes simplex encephalitis, cerebral malaria, and other arboviral diseases.3 There is no widely used antiviral treatment that specifically clears the virus. Care is supportive, including management of seizures, airway and breathing problems, raised intracranial pressure, and rehabilitation after the acute illness.
Vaccination is the principal method for preventing Japanese encephalitis in populations and travelers at meaningful risk.4 Several inactivated or live-attenuated vaccines are used in different countries, and national programs commonly target children in endemic areas because routine immunization can sharply reduce disease incidence. Travelers should seek individualized advice according to destination, season, itinerary, duration, and rural or outdoor exposure.
Mosquito avoidance complements vaccination: use an effective repellent, wear long sleeves and trousers, sleep in screened or air-conditioned rooms, and use bed nets when needed. Community measures include mosquito control, environmental management, and surveillance. Eliminating pigs alone is difficult because the virus also circulates among birds, and the ecology differs substantially between densely settled agricultural regions, islands, and temperate zones.2
Japanese encephalitis is not confined to Japan; its endemic and outbreak-prone range extends across much of South, Southeast, and East Asia and parts of the Western Pacific.1 The disease’s geography can change when irrigation, rice cultivation, urban expansion, animal production, or climate alter mosquito habitats. In some areas, transmission is seasonal; elsewhere it may occur throughout the year.
The burden does not end when fever resolves. Survivors can experience persistent seizures, movement abnormalities, learning difficulties, speech problems, behavioral changes, or other cognitive and neurological effects, creating long-term demands on families and health systems. A notable epidemiological shift has also occurred in several countries: successful childhood vaccination has reduced disease in children, while remaining cases may be proportionally more visible among adults who lack prior immunity. This pattern makes surveillance and vaccination policy important even where incidence has fallen.
Incidence and fatality estimates vary by surveillance quality, case definition, age distribution, and access to medical care; the figures shown are broad global estimates rather than counts for a single year.
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