Japanese Encephalitis Virus: The Emergence of Genotype IV in Australia and Its Potential Endemicity

Abstract

A fatal case of Japanese encephalitis (JE) occurred in northern Australia in early 2021. Sequence studies showed that the virus belonged to genotype IV (GIV), a genotype previously believed to be restricted to the Indonesian archipelago. This was the first locally acquired case of Japanese encephalitis virus (JEV) GIV to occur outside Indonesia, and the second confirmed fatal human case caused by a GIV virus. A closely related GIV JEV strain subsequently caused a widespread outbreak in eastern Australia in 2022 that was first detected by fetal death and abnormalities in commercial piggeries. Forty-two human cases also occurred with seven fatalities. This has been the first major outbreak of JEV in mainland Australia, and geographically the largest virgin soil outbreak recorded for JEV. This outbreak provides an opportunity to discuss and document the factors involved in the virus’ spread and its ecology in a novel ecological milieu in which other flaviviruses, including members of the JE serological complex, also occur. The probable vertebrate hosts and mosquito vectors are discussed with respect to virus spread and its possible endemicity in Australia, and the need to develop a One Health approach to develop improved surveillance methods to rapidly detect future outbreak activity across a large geographical area containing a sparse human population. Understanding the spread of JEV in a novel ecological environment is relevant to the possible threat that JEV may pose in the future to other receptive geographic areas, such as the west coast of the United States, southern Europe or Africa.

Little pig, little pig, let me come in: The influence of landscape structure and La Niña climatic anomalies on the emergence of Japanese encephalitis virus in Australian piggeries in 2022

“…These models allow the evaluation of spatial dependencies among JEV outbreaks in relation to landscape features and thus help to spatially demarcate risk. As a null model representing complete spatial randomness (CSR), JEV outbreaks were first fitted as a homogeneous Poisson process, with conditional intensity, λ(u,X) = β, [1] in which u represents outbreak (X) locations and β is the intensity parameter which signifies the number of points in a subregion of a defined spatial window. The expected intensity under CSR is simply proportional to the area of the subregion under investigation [57], indicating an absence of spatial dependency.…”

“…Japanese encephalitis virus (JEV) re-emerged in Australia over the 2021-2022 summer with extensive outbreaks in piggeries and sporadic cases in humans manifesting an unprecedented geographic distribution across Queensland, New South Wales (NSW), Victoria, and South Australia [1][2][3].…”

“…Japanese encephalitis virus (JEV) re-emerged in Australia over the 2021-2022 summer with extensive outbreaks in piggeries and sporadic cases in humans manifesting an unprecedented geographic distribution across Queensland, New South Wales (NSW), Victoria, and South Australia[1–3]. Previously, documented JEV circulation had been limited to very localised areas in the Torres Strait Islands[4] and the Cape York Peninsula of northern Queensland[5], but with evidence of regional ongoing circulation between southern Papua New Guinea, the Torres Strait Islands, and northern Australia[6].…”

Growth, Pathogenesis, and Serological Characteristics of the Japanese Encephalitis Virus Genotype IV Recent Strain 19CxBa-83-Cv

“…The first case of JE in humans caused by GIV JEV infection was reported in 2019 [ 31 ]. The endemics of JE in Australia in 2021 and 2022 were also caused by GIV JEV [ 38 , 39 , 40 ]. However, only a few GIV JEV have been isolated before the epidemics, little attention has been paid to GIV JEV, and GIV JEV has not been well characterized.…”

“…Genetic analysis of the JEV isolates from mosquitoes and pigs indicated that the isolates in 1998 also belonged to GII, whereas the isolate from Badu in the Torres Strait Islands in 2004 belonged to GI [ 36 , 37 ]. A JE patient who was thought to be infected with GIV JEV in the Tiwi islands in northern Australia was confirmed as infected in Australia in 2021 following a 20-year absence of JE [ 38 , 39 , 40 ]. In 2022, JEV was widespread in Australia.…”