Japanese encephalitis (JE) is the most important cause of viral encephalitis in Asia. It is caused by a flavivirus and is transmitted by mosquitoes. The World Health Organization estimates that there are approximately 50,000 cases of clinical disease per year with 10,000 deaths, mainly in children.
It is endemic in wet, rural areas, but can also occur in urban areas. Areas that are particularly risky are rice fields where mosquitoes thrive and where there is a lot of pig farming. Pigs and wading birds are the predominant hosts for this virus. Japanese encephalitis tends to be seasonal and cases occur mainly through the wet season.
JE is a rare disease in travellers, but it has a high fatality rate and there is a high rate of neuropsychiatric effects after recovery. There is a JE vaccine available for those who may be spending prolonged periods in endemic areas, although a risk assessment must be carefully considered as this vaccine can cause serious side effects.