Japanese encephalitis virus (JEV) is one of the leading causes of acute encephalitis in humans. The virus is spread by mosquitoes, mainly belonging to the Culex species. The main reservoirs are considered to be birds and pigs, with pigs constituting the most important reservoir in regard to human infection. During the last few decades the production of pork has increased significantly in Vietnam. With 90% of pigs being kept in households owning 10 pigs or less, pigs are widely spread across most parts of the country.