The detection of Japanese encephalitis virus in Megachiropteran bats in West Kalimantan, Indonesia: A potential enzootic transmission pattern in the absence of pig holdings

Mosquito vector competence for Japanese encephalitis virus: a systematic review and meta-analysis update

BACKGROUND

Japanese encephalitis is an emerging zoonotic disease caused by the Japanese encephalitis virus (JEV), transmitted primarily by mosquitoes of the Culex species. Amid the recent geographical expansion of JEV into Mainland Australia and the dramatic increase in research output, here we provide an update to our 2018 systematic review and meta-analysis, by appraising the scientific literature published from 2016 through 2023 and quantitatively summarizing the data from this update and the 2018 systematic review meta-analysis on vector competence for JEV.

METHODS

A systematic review of the literature on JEV vector and host competence, published from 2016 through 2023, was performed. Bibliographic databases, PubMed, Scopus, Web of Science, and the Armed Forces Pest Management Board website were searched for relevant literature. Records were screened for relevance for vector competence, specifically: infection rate, dissemination rate, and transmission rate. To estimate the overall and subgroup effect sizes for each mosquito species, random-effects meta-analysis models were utilized. Meta-regression models were fit to evaluate the association between a priori variables-such as mosquito subfamily/tribe, routes of JEV administration for mosquito infection, incubation length, incubation temperatures, and diagnostic methods for JEV detection-and the outcomes of interest.

RESULTS

This study update includes 74 new reports, identifying 9-12 additional mosquito species as competent for JEV, depending on the specific outcome assessed. The overall JEV infection, dissemination, and transmission rates across all species and studies were 45.4% (95% confidence interval (CI) 35.9-55.2%), 41.2% (95% CI 29.7-53.7%), and 22.7% (95% CI 14.6-33.4%), respectively. Among the subfamilies/tribes, Culicini had the highest infection (51.9%; 95% CI 39.2-64.4%) and transmission (27.8%; 95% CI 16.5-43.1%) rates. Meta-regressions showed mosquito subfamily/tribe was consistently associated with all the outcomes of interest, although the heterogeneity (I2) between studies remained consistently high (I2 > 83.47).

CONCLUSIONS

The information presented in this study provides a quantitative summary update on vector competence for JEV. Vector competence data are necessary for risk assessment models, the development of mosquito and virus surveillance programs, and effective prevention and control strategies in regions currently affected by JEV and those at risk of incursion.

Australian vertebrate hosts of Japanese encephalitis virus: a review of the evidence

Japanese encephalitis virus (JEV) transmission in temperate Australia has underscored a critical need to characterise transmission pathways and identify probable hosts of the virus. This systematic review consolidates existing research on the vertebrate hosts of JEV that are known to exist in Australia. Specifically, we aim to identify probable species involved in JEV transmission, their potential role as hosts and identify critical knowledge gaps. Data were extracted from studies involving experimental infection, seroprevalence and virus isolation and were available for 22 vertebrate species known to reside in Australia. A host competence score was calculated to assess the ability of each species to generate and sustain a viraemia. Based on the host competence score and ecology of each species, we find that ardeid birds, feral pigs and flying foxes have potential as maintenance hosts for JEV in the Australian context. We also note that domestic pigs are frequently infected during outbreaks, but their role as amplification hosts in Australia is unclear. Evidence to confirm these roles is sparse, emphasising the need for further targeted research. This review provides a foundation for future investigations into JEV transmission in Australia, advocating for enhanced surveillance and standardised research methodologies to better understand and mitigate the virus's impact.

Emerging zoonotic diseases in Southeast Asia in the period 2011-2022: a systematic literature review

As COVID-19 has shown, pandemics and outbreaks of emerging infections such as Zika, Nipah, monkeypox and antimicrobial-resistant pathogens, especially emerging zoonotic diseases, continue to occur and may even be increasing in Southeast Asia. In addition, these infections often result from environmental changes and human behaviour. Overall, public health surveillance to identify gaps in the literature and early warning signs are essential in this region. A systematic review investigated the prevalence of emerging zoonotic diseases over 11 years from 2011 to 2022 in Southeast Asia to understand the status of emerging zoonotic diseases, as well as to provide necessary actions for disease control and prevention in the region. During the 2011-2022 period, studies on pigs, poultry, ruminants, companion animals and wildlife in Southeast Asia were reviewed thoroughly to assess the quality of reporting items for inclusion in the systematic review. The review was performed on 26 studies of pigs, 6 studies of poultry, 21 studies of ruminants, 28 studies of companion animals and 25 studies of wildlife in Southeast Asia, which provide a snapshot of the prevalence of the emerging zoonotic disease across the country. The findings from the review showed that emerging zoonotic diseases were prevalent across the region and identified a few zoonotic diseases associated with poultry, mainly stemming from Cambodia and Vietnam, as high priority in Southeast Asia.Clinical relevance: Appropriate prevention and control measures should be taken to mitigate the emerging zoonotic diseases in Southeast Asia.

Japanese encephalitis virus: epidemiology and risk-based surveillance approaches for New Zealand

The introduction and subsequent rapid spread of Japanese encephalitis virus genotype IV across all Australian mainland states and the Northern Territory since late 2021 has increased the risk of an incursion of this mosquito-transmitted zoonotic virus disease into New Zealand, with serious implications for both animal and human health. The potential modes of entry are through introduction of infected mosquitoes as hitchhikers on ships or aircraft, windborne transfer of mosquitoes, or arrival of infected reservoir bird species. A competent vector mosquito, Culex quinquefasciatus, is endemic in New Zealand and other mosquito species may also become involved. If infection becomes established in New Zealand, the scale of transmission may be considerably less than has occurred in Australia because climatic and epidemiological factors are not so favourable. Early evidence of an incursion could come from detection of clinical disease in horses or pigs, or from human cases. Targeted surveillance to confirm or refute indications of an incursion could be undertaken by antibody detection in a number of species. Dogs have been shown to be a particularly valuable sentinel species due to their cohabitation with people and high seroconversion rate. Other novel methods of surveillance could include reverse transcriptase PCR (RT-PCR) on oronasal secretions of pigs. Should evidence of the disease be detected, prompt action would be required to vaccinate at-risk human populations and clarify the epidemiological situation with respect to mammalian hosts and mosquito vector species, including whether a new mosquito species had arrived in the country.Abbreviations: AHL: Animal Health Laboratory; JE: Japanese encephalitis disease; JEV: Japanese encephalitis virus; RT-PCR: Reverse transcriptase PCR.

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

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.

Estimation of Japanese encephalitis virus infection prevalence in mosquitoes and bats through nationwide sentinel surveillance in Indonesia

Indonesia belongs to endemic areas of Japanese encephalitis (JE), yet data regarding the true risk of disease transmission are lacking. While many seroprevalence studies reported its classic enzootic transmission, data related to the role of bats in the transmission of JE virus are limited. This current study aimed to identify the potential role of bats in the local transmission of the JE virus to aid the ongoing active case surveillance in Indonesia, in order to estimate the transmission risk. Mosquitoes and bats were collected from 11 provinces in Indonesia. The detection of the JE virus used polymerase chain reaction (PCR). Maps were generated to analyze the JE virus distribution pattern. Logistic regression analysis was done to identify risk factors of JE virus transmission. JE virus was detected in 1.4% (7/483) of mosquito pools and in 2.0% (68/3,322) of bat samples. Mosquito species positive for JE virus were Culex tritaeniorhynchus and Cx. vishnui, whereas JE-positive bats belonged to the genera Cynopterus, Eonycteris, Hipposideros, Kerivoula, Macroglossus, Pipistrellus, Rousettus, Scotophilus and Thoopterus. JE-positive mosquitoes were collected at the same sites as the JE-positive bats. Collection site nearby human dwellings (AOR: 2.02; P = 0.009) and relative humidity of >80% (AOR: 2.40; P = 0.001) were identified as independent risk factors for JE virus transmission. The findings of the current study highlighted the likely ongoing risk of JE virus transmission in many provinces in Indonesia, and its potential implications on human health.