Journal of Mosquito Research, 2024, Vol.14, No.5, 247-255 http://emtoscipublisher.com/index.php/jmr 248 2 Overview of Japanese Encephalitis 2.1 Virology and epidemiology Japanese Encephalitis (JE) is caused by the Japanese Encephalitis Virus (JEV), a mosquito-borne flavivirus. JEV is primarily transmitted by mosquitoes of the Culex genus, particularly Culex tritaeniorhynchus, and is endemic in many parts of Southeast Asia and the Western Pacific (Oliveira et al., 2018; Pearce et al., 2018). The virus is known for causing severe encephalitis in humans, with a high mortality rate and significant long-term neurological sequelae in survivors (Mulvey et al., 2021). Despite the availability of effective vaccines, JE remains a leading cause of viral encephalitis in Asia, particularly affecting children under 14 years old. The epidemiology of JE is complex, involving various environmental, ecological, and social determinants that influence its transmission and geographic spread. 2.2 Transmission cycle and primary vectors The transmission cycle of JEV is intricate, involving multiple hosts and vectors. The primary vectors are mosquitoes of the Culex genus, with Culex tritaeniorhynchus being the most significant in many regions (Mulvey et al., 2021). Pigs serve as the main amplifying hosts, while ardeid birds, such as egrets and herons, act as natural reservoirs (Oliveira et al., 2018; Mulvey et al., 2021). During outbreaks, pigs play a crucial role in amplifying the virus, which is then transmitted to humans through mosquito bites (Figure 1) (Ladreyt et al., 2019; Mulvey et al., 2021). Human infection is considered a dead end in the virus's life cycle, as humans do not contribute to further transmission (Pearce et al., 2018). Other mosquito species, such as Culex annulirostris, Culex quinquefasciatus, and Culex sitiens, have also been identified as potential vectors, particularly in regions like Australia where JEV has recently emerged (Furlong et al., 2022; Hurk et al., 2022; Furlong et al., 2023). Figure 1 Overview of the Japanese encephalitis virus transmission cycle (Adopted from Mulvey et al., 2021) 2.3 Geographic distribution and affected populations JE is predominantly found in Southeast Asia, the Western Pacific, and parts of the Pacific Islands. However, recent outbreaks in regions like southeastern Australia indicate an expanding geographic range, likely influenced by factors such as climate change, urbanization, and changes in agricultural practices (Pearce et al., 2018; Furlong et al., 2022; Hurk et al., 2022; Furlong et al., 2023). In Australia, the primary vectors include Culex annulirostris and Culex sitiens, with significant presence along the eastern and northern coastlines. The affected populations are primarily rural communities with close proximity to rice paddies, pig farms, and water bodies, which provide ideal breeding grounds for the mosquito vectors (Liu et al., 2018; Pearce et al., 2018; Furlong et al., 2023). Children are particularly vulnerable to JE, with the highest incidence rates observed in those under 14 years old. The disease's impact on human health underscores the need for increased surveillance, vaccination, and targeted vector control measures to mitigate the risk of JE transmission (Oliveira et al., 2018; Ladreyt et al., 2019; Mulvey et al., 2021).
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