# An Overview of Japanese Encephalitis in Australia: Trends, Impact and Interventions
## 1 Epidemiology of Japanese Encephalitis and the Outbreak in Australia  
Globally, there are an estimated 68,000-100,000 clinical JE cases annually, causing approximately 15,000-25,000 fatalities [1, 2]. Although historically most common in countries such as Japan and China, large-scale vaccination programmes have significantly reduced infection rates in these populations [2]. On 4 March 2022, an identified outbreak of Japanese Encephalitis (JE) in Australia was declared a \"communicable disease incident of national significance\" by Australia's Acting Chief Medical Officer, Dr. [PERSON] [3, 4]. At this time, Dr. [PERSON] called for a national approach to the \"coordination of health policy, interventions and public messaging\" surrounding this new outbreak [5]. Cases of Japanese encephalitis virus (JEV) infection have been found in piggiers across New South Wales and Victoria since January of that year, with more identified in Queensland and South Australia in the following months [6]. Australia's Chief Veterinary Officer, Dr. [PERSON], noted that disease symptoms were most likely to be seen in piglets, with increased rates of stillbirth, impaired neurological functioning and hindlimb paralysis observed in the affected animal populations [5]. After identifying these animal cases in temperate regions of Australia not typically associated with the disease, it was hypothesised that the first human fatality from JE documented in the country since 1998, which occurred in February 2021, was actually the sentinel human case for the 2022 epidemic [3]. As such, this single case heralded a new infectious disease outbreak that would cause 40 further infections and 5 deaths by August 2022 [6]. Linked genetically to this sentinel case, the JEV genotype responsible for the recent outbreak has been identified as genotype IV, a previously rare variant found in China, Indonesia, Malaysia and Papua New Guinea [7]. The most recent media release from the Australian government in June 2023 reported a total of 45 human cases (35 withlaboratory confirmation and 10 probable cases linked epidemiologically) and 7 deaths associated with the outbreak [8; 9]. As no new cases have been detected in the Australian population since December 2022, the communication also announced the standing down of the JEV emergency response. While this was not the first outbreak of JE in Australia, the situation was unique, as it occurred against the backdrop of an ongoing global pandemic of another communicable disease (COVID-19). The genotype involved in the outbreak (genotype IV) is also different from the two previous JEV outbreaks (I in 1995 and II in 1998) [10]. Although JEV was known to circulate in Queensland in the ten years following the 1995 outbreak, there are numerous theories as to why it is suddenly following a different pattern of expansion now. [PERSON] et al. noted that 2021 and 2022 were La Nina years with high levels of rainfall typically associated with outbreaks of mosquito-borne zoonotic infections [10]. Unprecedented flooding events have also likely contributed to JEV's emergence in Australia's mainland [11]. There is some evidence that endemicity in feral pig populations has already been established, and while JEV is a notifiable disease in both animals and humans in Australia, the contribution of these animals to the overall zoonotic infection rate is unknown [8; 11]. Climate change plays a major role in vector-borne disease transmission, with rain and flood water providing the environmental conditions for mosquito population growth due to an \"abundance of larval habitats,\" and other weather conditions promoting different migration patterns for birds and other animal populations who are potential reservoirs of infection [12; 13; 14]. [PERSON] et al. noted that the incursion of JEV into southeastern Australia represents a shift \"at least 2500 km below its previous southern geographical limit\" (Figure 1) [12].