A mosquito-borne virus that turns the brain against itself

Health · Published 3 October 2026 Swipe more like this →

In short: Japanese encephalitis is a rare but devastating viral infection that primarily affects children in Asia. While most infections cause only mild symptoms, the virus can trigger a severe inflammatory response in the brain. With no known cure, the disease remains a significant public health challenge across twenty-four countries.

Japanese encephalitis virus (JEV) is a flavivirus, sharing a family with dengue, yellow fever, and West Nile virus. It persists in an enzootic cycle involving mosquitoes, particularly the Culex tritaeniorhynchus species, and vertebrate hosts like domestic pigs and water birds. Humans are accidental hosts; while we can be infected through mosquito bites, we do not develop enough virus in our blood to pass it back to the insects. The disease is most common in rural and periurban areas where humans live in close proximity to these animal reservoirs.

The clinical reality of the infection is stark. While only about 1 in 250 infections result in severe illness, the consequences are profound. The virus invades the central nervous system, causing an acute inflammatory response. Research suggests that this triggers an autotoxic loop where the brain's own immune cells, known as microglia, become overactive. These cells release proinflammatory cytokines and neurotoxins that, while intended to fight the virus, can cause significant bystander damage to healthy neurons in a non-regenerating organ.

The mortality rate for symptomatic cases can reach 30%, and survivors face a high risk of long-term disability. Between 30% and 50% of those who recover experience permanent cognitive, behavioural, or neurological sequelae, including seizures, paralysis, and speech or vision loss. Because there is no antiviral treatment, medical care focuses entirely on supportive therapy and symptom management. Vaccination remains the most effective tool for prevention, and the World Health Organization strongly recommends integrating it into national immunization schedules in all endemic regions.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

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