- Japanese encephalitis (JE) is a mosquito-borne viral disease caused by the Japanese encephalitis virus (JEV), a member of the Flavivirus genus in the Flaviviridae family. It is the leading cause of viral encephalitis in Asia, with an estimated 68,000 clinical cases reported annually, although many more go undiagnosed or unreported. The virus is endemic in parts of Southeast Asia, the Western Pacific, and increasingly parts of South Asia, with transmission peaking during and after the rainy season when mosquito populations surge.
- The primary vectors of JEV are mosquitoes from the Culex species, particularly Culex tritaeniorhynchus, which breed in rice paddies, irrigation canals, and other stagnant water sources in rural and agricultural areas. These mosquitoes feed mainly during dusk and nighttime. The virus maintains a natural transmission cycle between mosquitoes, water birds (such as herons and egrets), and pigs, which are considered important amplifying hosts. Humans are incidental or “dead-end” hosts, as they do not develop sufficient levels of the virus in their blood to infect feeding mosquitoes.
- Most human infections with JEV are asymptomatic or result in mild symptoms, such as fever and headache. However, in a small percentage of cases—approximately 1 in 250—the virus invades the central nervous system, causing encephalitis, a potentially life-threatening inflammation of the brain. Symptoms of Japanese encephalitis can include high fever, stiff neck, seizures, disorientation, coma, and paralysis. The case fatality rate among severe cases can be as high as 30%, and 20–50% of survivors may suffer from long-term neurological or psychiatric complications, including cognitive deficits, behavioral changes, and motor impairments.
- Diagnosis of Japanese encephalitis is based on clinical presentation and confirmed through laboratory tests such as IgM antibody detection in cerebrospinal fluid or blood. There is no specific antiviral treatment for JEV. Care is supportive and focused on managing complications like seizures, reducing intracranial pressure, and preventing secondary infections.
- The most effective method of preventing Japanese encephalitis is vaccination. Several safe and effective vaccines are available and widely used in endemic regions, particularly as part of childhood immunization programs. In addition to vaccination, vector control efforts—such as reducing mosquito breeding grounds, using bed nets and repellents, and minimizing outdoor exposure during peak mosquito activity—play an important role in reducing transmission.
- Due to its potentially devastating neurological impact and the lack of curative treatment, Japanese encephalitis remains a significant public health concern in affected regions. Continued investment in vaccination programs, surveillance, and mosquito control is essential to preventing outbreaks and protecting vulnerable populations, especially children in rural farming communities.
