JEV is a flavivirus related to dengue, yellow fever, and West Nile viruses, and is spread by mosquitoes (mainly the Culex species). It is the main cause of viral encephalitis in many countries of Asia and there is no cure for the disease however vaccines are available. Most infections are mild, however, 1 in 250 infections results in severe disease which can lead to death (30% fatality rate) or permanent disability such as paralysis, recurrent seizure or the inability to speak. The WHO recommends testing for JEV-specific IgM antibodies in a single sample of cerebrospinal fluid (CSF) or serum, using an IgM-capture ELISA. Testing of CSF samples is preferred to reduce false-positivity rates from previous infection or vaccination.