Neville Peter J, Evans Rachel N, O'Brien Helen, Mee Peter T, Brohier Natasha D, Hughes Nicole
Communicable Disease Prevention and Control, Department of Health, Melbourne, Victoria, Australia.
Agriculture Victoria Research, AgriBio Centre for AgriBioscience, Bundoora, Melbourne, Victoria, Australia.
PLoS Negl Trop Dis. 2025 Aug 18;19(8):e0013407. doi: 10.1371/journal.pntd.0013407. eCollection 2025 Aug.
The sporadic yet explosive nature of Murray Valley encephalitis virus (MVEV) in the southeast of Australia has led to several hypotheses to explain the viruses temporal and spatial patterns in the region. These theories, relying on the presence of flooding events, include the role of migratory waterbirds as carriers of MVEV from endemic areas in northern Australia or the re-appearance of MVEV from isolated, cryptic habitats. Here we describe the environmental, climatic and entomological factors that led to the development of the "perfect swarm" and re-emergence of MVEV in Victoria during the 2022-23 mosquito season, allowing greater scrutiny of the proposed theories for MVEV outbreaks in the southeast of Australia.
Mosquitoes were collected using Encephalitis Virus Surveillance Carbon Dioxide (EVS CO2) traps that were set weekly across 17 northern Victorian Local Government Authorities (LGAs). Trapped mosquitoes were counted, speciated and screened for known viruses of public health significance. Mosquito abundance and species composition was compared with climatic variables including temperature and rainfall.
A positive Southern Oscillation Index and a significant rainfall event in October 2022 led to flooding in central and northern Victoria that persisted for many months. Dominance of the mosquito fauna by Culex australicus in October to December 2022, followed by Culex annulirostris over January to March 2023 provided the vectors for amplification and subsequent transmission of MVEV within hosts, leading to spill-over into human populations for the first time in Victoria in almost 50 years. Mosquito surveillance systems detected MVEV in 48 mosquito traps over a 13-week period commencing in the first week of 2023. Virus positive species-specific pools included Cx. australicus and Cx. annulirostris, implicating both species as playing a role in MVEV amplification and/or transmission. Typing of MVEV was determined to be closely related to MVEV serotype G1A sub-lineage, which had previously only been detected in northwest Australia and from a human case in the Northern Territory.
The detection of MVEV during the 2022-23 mosquito season in south-eastern Australia provides greater context for understanding the re-appearance of MVEV in this region, with increased evidence implicating the role of migratory waterbirds, in response to flooding events, as carriers of MVEV into south-eastern Australia.
澳大利亚东南部墨累谷脑炎病毒（MVEV）具有散发性但爆发性的特点，这引发了多种假说以解释该病毒在该地区的时空分布模式。这些依赖于洪水事件存在的理论包括：迁徙水鸟作为MVEV从澳大利亚北部流行地区的携带者的作用，或者MVEV从孤立的隐秘栖息地再次出现。在此，我们描述了导致2022 - 2023年蚊虫季节维多利亚州出现“完美群体”以及MVEV再次出现的环境、气候和昆虫学因素，从而能够更深入地审视关于澳大利亚东南部MVEV爆发的提出的理论。
使用脑炎病毒监测二氧化碳（EVS CO₂）诱捕器收集蚊子，这些诱捕器每周在维多利亚州北部的17个地方政府辖区（LGAs）设置。对捕获的蚊子进行计数、分类，并筛查具有公共卫生意义的已知病毒。将蚊子的丰度和物种组成与包括温度和降雨在内的气候变量进行比较。
2022年10月正的南方涛动指数和一次显著降雨事件导致维多利亚州中部和北部发生洪水，洪水持续了数月。2022年10月至12月澳大利亚库蚊在蚊虫群落中占主导地位，随后在2023年1月至3月环纹库蚊占主导地位，这为MVEV在宿主体内的扩增和随后传播提供了媒介，导致近50年来MVEV首次在维多利亚州传播到人类群体。蚊虫监测系统在从2023年第一周开始的13周内，在48个蚊虫诱捕器中检测到了MVEV。病毒阳性的物种特异性样本包括澳大利亚库蚊和环纹库蚊，这表明这两个物种在MVEV扩增和/或传播中都发挥了作用。MVEV的分型被确定与MVEV血清型G1A亚谱系密切相关，该亚谱系此前仅在澳大利亚西北部以及北领地的一例人类病例中被检测到。
2022 - 2023年蚊虫季节在澳大利亚东南部检测到MVEV，为理解该地区MVEV的再次出现提供了更多背景信息，越来越多的证据表明，迁徙水鸟作为MVEV的携带者，在洪水事件的影响下，将MVEV带入了澳大利亚东南部。
