Japanese Encephalitis

A flavivirus spread by Culex mosquitoes (amplified in pigs and wading birds), historically confined to Asia and the Western Pacific.

Clinical features

Most infections are asymptomatic or mild. A small proportion (<1%) develop encephalitis — headache, fever, disorientation, tremor, convulsions, progressing to coma — with a high case-fatality rate and frequent neurological sequelae in survivors.

Diagnosis and management

• JE virus IgM/IgG (serum ± CSF); MRI/CSF to support encephalitis.
• No specific antiviral — supportive hospital care for encephalitis (and to exclude bacterial meningitis).
• Vaccination (JEspect / Imojev) is recommended for people moving to or spending ≥1 month in endemic areas, frequent travellers, and now for at-risk Australian residents/occupations (see below).

Japanese encephalitis has established itself on mainland Australia — detected in piggeries across the Murray–Darling basin (Vic/NSW/Qld/SA) from early 2022, with human cases and deaths, and declared a Communicable Disease Incident of National Significance. State-funded JE vaccination programs now cover at-risk residents and occupations (piggery/abattoir workers, those living/working near affected waterways) — check current local advice.