Japanese encephalitis virus: changing the clinical landscape of encephalitis in Australia

To the Editor: We write in response to the excellent review by Allen and colleagues1 and to highlight the recent introduction of national surveillance for Japanese encephalitis by the Australian Paediatric Surveillance Unit (APSU) (www.apsu.org.au).

Japanese encephalitis virus (JEV) is a mosquito‐borne flavivirus that is endemic in South‐East Asia and may cause severe encephalitis. In March 2022, Australian health authorities notified the World Health Organization of a JEV outbreak on the east coast of Australia, which included 37 human cases of JEV infection in New South Wales, Victoria, South Australia, and Queensland and represented the first locally acquired JEV infections since 1998.2

As of 14 August 2023, there have been 45 cases reported with JEV infection (14 in NSW, 14 in Victoria, ten in SA, five in Queensland, and two in the Northern Territory) and seven deaths.3 The JEV variant identified in all cases was genotype 4 (GIV), which has been only previously isolated in Indonesia and Papua New Guinea4 (Box), and very little is known about its virulence or pathogenesis. In most endemic countries, 75% of Japanese encephalitis cases occur in children aged zero to 14 years. In the current Australian outbreak, of the JEV infection cases reported since 2022, 10% of patients (all male) were aged 19 years or younger.

It is speculated that JEV may become endemic in Australia, and modelling suggests that about 3% (~750000) of the Australian human population is at risk of JEV infection due to their proximity to piggeries.5,6,7

Allen and colleagues1 mentioned the importance of adequate surveillance platforms, highlighting that notification systems are more efficient in identifying laboratory‐confirmed diseases.7 In response to the emergence of JEV in Australia, the APSU commenced national active surveillance in May 2023 to identify cases of Japanese encephalitis in children aged 17 years or younger, and to describe the demographic characteristics, clinical features, treatment, and short term outcomes.

• acute symptoms (eg, high fever, rigors, headache, vomiting, seizures, rash); or
• later stage symptoms/signs (eg, altered level of consciousness, seizures, parkinsonian‐like symptoms, paralysis, cranial nerve palsies); and
• laboratory confirmation of acute JEV infection — detection of JEV IgM (serum and/or cerebrospinal fluid), and/or IgG seroconversion (serum), and/or positive JEV polymerase chain reaction (cerebrospinal fluid, blood, urine).1

Please email schn‐apsu@health.nsw.gov.au if you wish to contribute.

Box – Japanese encephalitis virus (JEV) geographic areas

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