The Ecology and Evolution of Japanese Encephalitis Virus

Abstract

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus mainly spread by Culex mosquitoes that currently has a geographic distribution across most of Southeast Asia and the Western Pacific. Infection with JEV can cause Japanese encephalitis (JE), a severe disease with a high mortality rate, which also results in ongoing sequalae in many survivors. The natural reservoir of JEV is ardeid wading birds, such as egrets and herons, but pigs commonly play an important role as an amplifying host during outbreaks in human populations. Other domestic animals and wildlife have been detected as hosts for JEV, but their role in the ecology and epidemiology of JEV is uncertain. Safe and effective JEV vaccines are available, but unfortunately, their use remains low in most endemic countries where they are most needed. Increased surveillance and diagnosis of JE is required as climate change and social disruption are likely to facilitate further geographical expansion of Culex vectors and JE risk areas.

The pig as an amplifying host for new and emerging zoonotic viruses

“…Culex spp. mosquitoes transmit JEV from animals to humans [ [28] , [29] , [30] ]. Ardeid birds are thought to be the natural reservoirs for JEV, pigs in turn are the main amplifying host, and Culex mosquitoes are the vectors in the transmission cycle [ [30] , [31] , [32] ].…”

“…mosquitoes transmit JEV from animals to humans [ [28] , [29] , [30] ]. Ardeid birds are thought to be the natural reservoirs for JEV, pigs in turn are the main amplifying host, and Culex mosquitoes are the vectors in the transmission cycle [ [30] , [31] , [32] ]. Interestingly, more recent findings have implicated that direct transmission between pigs can occur via oronasal virus shedding [ 33 ].…”

Adaptive Evolution as a Driving Force of the Emergence and Re-Emergence of Mosquito-Borne Viral Diseases

“…Despite the successful vaccination and eradication programs in some economically affluent Asian countries, the distribution of JEV in Southeast Asia continues to grow. Recently, the Tiwi Islands in the Northern Territory of Australia reported its first JEV case in 2021 [21], while cases of indigenous JEV infection were detected in Angola in 2016 [22], raising concerns about future outbreaks in these regions.…”

Japanese Encephalitis emergence in Australia: the potential population at risk

“…This is the genotype associated with the 2021 case from the Tiwi Islands. It is not the genotype isolated during the 1995 and 1998 Australian outbreaks (I, II) nor one of the genotypes that dominate Asia (I, II, III [1]). Genotype IV is currently circulating in Indonesia [1, 8].…”

“…Until 2022, the southerly limit of the disease was the far north of Australia where, in 1995 there were three cases and two deaths on Badu Island [2], and a further two cases from the same island and neighbouring Cape York peninsula in 1998 (one case recovered, one with ongoing cognitive challenges) [3]. An additional death, associated with JEV exposure in the Tiwi Islands (Northern Territory, Australia) occurred in 2021 [1]. In far north Queensland (QLD), JEV was recovered annually from mosquitoes and/or domestic pigs (including sentinel animals) in 1995-1998, and 2000-2005.…”