The expanding reach of Japanese encephalitis

Author(s):  Dr Sherilyn Houle

Japanese encephalitis (JE) has largely been regarded as a virus affecting Asia and the western Pacific,  with a seasonal pattern over summer months in temperate areas and rainy season in the tropics and subtropics.¹ However, climate change, novel host species (e.g., ticks, domestic cattle and sheep, pangolins, meerkats),² changing bird migration patterns, and other factors appear to be contributing to a more dynamic picture of this virus.

Geographic regions impacted may be expanding, with one local human case confirmed in Angola (the first case in Africa) in 2016 and 46 human cases and 7 deaths in Australia from an outbreak spanning 2022-2023.^2-3 While the source of infection and its transmission for the case in Angola is unknown,⁴ ecological modelling found that regions with elevated suitability for the virus exist along Australia’s east and southwestern coasts, with spillover possible to large parts of eastern and southern Australia.³ While the virus has also been detected in mosquito and bird hosts in Europe, no new evidence of active transmission has been reported there in over a decade.²

Clinical resources are recognizing JE as a risk in certain parts of Australia, with the CDC identifying it as a concern specifically in the Murray River and Outer Torres Strait Islands areas,⁵ and TravelHealthPro and Shoreland Travax listing broader regions including parts of Victoria, New South Wales, Queensland, Western Australia, South Australia, and the Northern Territory.^6-7

Decision-making around vaccination for JE is complex and considers destination, itinerary, duration and season of travel, and other factors. In addition to keeping current on virus epidemiology, providers can find a free JE vaccine decision aid to assist with these conversations at https://www.monash.edu/medicine/sphpm/vaccinedecisionaids-je/home

References

[1].  Japanese encephalitis.  World Health Organization [link]
[2].  Spatiotemporal Distribution and Host-Vector Dynamics of Japanese Encephalitis Virus.  Yin Q, Li B, Wang R, et al. ‐ Viruses 2025;17(6):815 [link]
[3].  Ecological suitability of Japanese encephalitis virus in Australia: A modelling analysis of vector-host transmission dynamics to potential spillover in humans.  Skinner EB, Sartorius B, Furuya-Kanamori L, et al. ‐ PLoS Negl Trop Dis 2025;19(11): e0013722. [link]
[4].  Review of Emerging Japanese Encephalitis Virus: New Aspects and Concepts about Entry into the Brain and Inter-Cellular Spreading.  Filgueira L, Lannes N. ‐ Pathogens 2019;8(3):111. [link]
[5].  CDC Travelers’ Health: Australia.  Centers for Disease Control and Prevention. [link]
[6].  Country Information: Australia.  TravelHealthPro [link]
[7].  Destinations: Australia.  Shoreland Travax [link]