Japanese encephalitis disease: overview of the virus, its risk to Australia and the need for better surveillance

Abstract

Japanese encephalitis disease: overview of the virus, its risk to Australia and the need for better surveillance Japanese encephalitis virus (JEV) re-emerged in Australia in 2021, initially as a fatal case from the Tiwi Islands north of Darwin. Sequencing studies showed the virus causing the outbreak was a JEV genotype IV (GIV) virus. Encephalitis caused by JEV GIV appeared to be indistinguishable from encephalitis caused by other JEV genotypes or other members of the Japanese encephalitis (JE) serological complex such as Murray Valley encephalitis virus (MVEV) and West Nile virus (WNV).A fatal case of JE occurred in the Northern Territory (NT) in March 2021 in a 45-year-old resident of the Tiwi Islands. 1,2 This was the first recorded case of JE acquired in Australia since 1995-1998 when five cases of encephalitis, two of them fatal, had occurred on Badu, an island in the central Torres Strait, and on Cape York near the mouth of the Mitchell River. 3 The 2021 Tiwi Island case was the sentinel case for a subsequent widespread outbreak of JE that was first detected in February 2022, associated with mummified and stillborn piglets in over 80 piggeries in southern Queensland, New South Wales (NSW), northern Victoria and eastern South Australia (SA). 4 It also resulted in 42 human cases in the four states, seven of them fatal. 5 JEV, a mosquito-transmitted flavivirus, is the most important vaccine-preventable cause of viral encephalitis in Asia 6,7 and is known for its high mortality and high frequency of severe sequelae in symptomatic cases. It is thought to cause the loss of 709 000 disability-adjusted life years annually, making it one of the most important human arboviral diseases. 8,9 The geographic distribution of JEV extends from eastern Asia in maritime Russia, Japan, Korea and China to South-East Asia from the Philippines to Vietnam, Malaysia and Thailand, and southern Asia from Indonesia to India, Nepal and Sri Lanka. It also spread into Papua New Guinea and the Torres Strait islands of north-eastern Australia. 10 It is closely related antigenically and genetically to the Australian flaviviruses, MVEV and WNV (Kunjin strain) viruses. This close antigenic relationship can make serological diagnoses difficult, especially as prior exposure to a flavivirus can often result in higher antibody levels to a previous virus than to a different newly infecting flavivirus. 11 Laboratory testing and the interpretation of results