Japanese encephalitis (JE) is a viral disease characterized by inflammation of the brain. Symptoms include high fever, headache, fatigue, nausea, vomiting, confusion, and in severe cases, seizures, paralysis and coma. There is no specific treatment. Severe illnesses are treated by supportive therapy which may include hospitalization, respiratory support and intravenous fluids. JE is fatal in up to 30% of cases. Among survivors, 30-50% have long-term neurologic sequelae.
JE virus is transmitted by mosquitoes in a cycle with water birds and sometimes pigs. JE virus transmission occurs across broad areas of Asia and the Western Pacific, including parts of 24 countries: Australia, Bangladesh, Bhutan, Brunei Darussalam, Cambodia, China, Democratic People’s Republic of Korea, India, Indonesia, Japan, Lao People’s Democratic Republic, Malaysia, Myanmar, Nepal, Pakistan, Papua New Guinea, Philippines, Republic of Korea, Russian Federation, Singapore, Sri Lanka, Thailand, Timor-Leste, and Viet Nam. JE usually occurs in rural or agricultural areas, often associated with rice farming. In temperate areas of Asia, transmission is seasonal, and human disease usually peaks in the summer and fall. In the subtropics and tropics, transmission can occur year-round, often with a peak during the rainy season.
Most infections with JE virus result in mild symptoms or no symptoms at all. However, around 1 in 300 infections results in encephalitis. Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. Vaccination against JE virus is the single most important preventive measure.
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