Williams David T, Diviney Sinéad M, Niazi Aziz-ur-Rahman, Durr Peter A, Chua Beng Hooi, Herring Belinda, Pyke Alyssa, Doggett Stephen L, Johansen Cheryl A, Mackenzie John S
CSIRO, Australian Animal Health Laboratory, Geelong, Victoria, Australia.
Faculty of Health Sciences, Curtin University, Perth, Western Australia, Australia.
PLoS Negl Trop Dis. 2015 Nov 24;9(11):e0004240. doi: 10.1371/journal.pntd.0004240. eCollection 2015 Nov.
Recent increased activity of the mosquito-borne Murray Valley encephalitis virus (MVEV) in Australia has renewed concerns regarding its potential to spread and cause disease.
METHODOLOGY/PRINCIPAL FINDINGS: To better understand the genetic relationships between earlier and more recent circulating strains, patterns of virus movement, as well as the molecular basis of MVEV evolution, complete pre-membrane (prM) and Envelope (Env) genes were sequenced from sixty-six MVEV strains from different regions of the Australasian region, isolated over a sixty year period (1951-2011). Phylogenetic analyses indicated that, of the four recognized genotypes, only G1 and G2 are contemporary. G1 viruses were dominant over the sampling period and found across the known geographic range of MVEV. Two distinct sub-lineages of G1 were observed (1A and 1B). Although G1B strains have been isolated from across mainland Australia, Australian G1A strains have not been detected outside northwest Australia. Similarly, G2 is comprised of only Western Australian isolates from mosquitoes, suggesting G1B and G2 viruses have geographic or ecological restrictions. No evidence of recombination was found and a single amino acid substitution in the Env protein (S332G) was found to be under positive selection, while several others were found to be under directional evolution. Evolutionary analyses indicated that extant genotypes of MVEV began to diverge from a common ancestor approximately 200 years ago. G2 was the first genotype to diverge, followed by G3 and G4, and finally G1, from which subtypes G1A and G1B diverged between 1964 and 1994.
CONCLUSIONS/SIGNIFICANCE: The results of this study provides new insights into the genetic diversity and evolution of MVEV. The demonstration of co-circulation of all contemporary genetic lineages of MVEV in northwestern Australia, supports the contention that this region is the enzootic focus for this virus.
最近澳大利亚蚊媒传播的墨累谷脑炎病毒（MVEV）活动增加，这再次引发了人们对其传播和致病潜力的担忧。
方法/主要发现：为了更好地了解早期和近期流行毒株之间的遗传关系、病毒传播模式以及MVEV进化的分子基础，对来自澳大拉西亚地区不同区域、在60年期间（1951 - 2011年）分离出的66株MVEV毒株的完整前膜（prM）和包膜（Env）基因进行了测序。系统发育分析表明，在四种公认的基因型中，只有G1和G2是同时期存在的。在整个采样期间，G1病毒占主导地位，且在MVEV已知地理范围内均有发现。观察到G1有两个不同的亚谱系（1A和1B）。尽管G1B毒株已在澳大利亚大陆各地分离得到，但澳大利亚的G1A毒株仅在澳大利亚西北部以外未被检测到。同样，G2仅由来自西澳大利亚蚊子的分离株组成，这表明G1B和G2病毒存在地理或生态限制。未发现重组证据，并且发现包膜蛋白中的一个氨基酸替换（S332G）处于正选择之下，而其他几个替换则处于定向进化之下。进化分析表明，MVEV现存的基因型大约在200年前开始从一个共同祖先分化出来。G2是第一个分化的基因型，随后是G3和G4，最后是G1，G1的亚型G1A和G1B在1964年至1994年间分化。
结论/意义：本研究结果为MVEV的遗传多样性和进化提供了新的见解。MVEV所有当代遗传谱系在澳大利亚西北部共同循环的证明，支持了该地区是这种病毒的动物疫源地这一论点。
