Diagnostic Laboratory, School of Veterinary Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, Greece.
National Reference Centre for Arboviruses, Department of Microbiology, Medical School, Faculty of Health Sciences, Aristotle University of Thessaloniki, Greece.
Mol Phylogenet Evol. 2019 Dec;141:106617. doi: 10.1016/j.ympev.2019.106617. Epub 2019 Sep 12.
West Nile virus (WNV) is an arbovirus causing neuroinvasive disease to humans and equines. Since 2004, lineage 2 WNV strains have been identified in Europe and have been implicated in severe outbreaks, with that of 2018 exceeding the total number from the previous seven years. The aim of this study was to explore the evolutionary process that shapes the genetic diversity of lineage 2 WNV strains (belonging to the Central European/Hungarian subclade) and reconstruct the origin and transmission routes in Europe, and especially in the Balkans. For this purpose, a high number of whole genome sequences (WGSs) were analyzed, along with newly characterized sequences, including strains from the 2018 WNV transmission season in Greece. Maximum likelihood and Bayesian inference methods were used to perform the phylogenetic and phylodynamic analyses and phylogeographic reconstruction. The majority of the Central European/Hungarian lineage 2 strains are grouped in 2 phylogenetic subgroups (Central/South-West European and Balkan) with bush-like topology. Purifying selection shapes their evolution, however, strong evidence of positive selection was revealed in 7 non-structural protein codons of NS1, NS4B and NS5. Thirty-two amino-acid substitutions were fixed in different phylogenetic subgroups, indicating that random genetic drift is responsible for the majority of evolutionary changes. Virus migration, followed by subsequent local evolution is responsible for continuously evolving strains throughout Europe. In total, 10 virus transitions between discrete geographical locations, involving virus spread from Central Europe to other regions, were highly supported. Three novel, independent introductions from Hungary and Bulgaria were responsible for the 2018 re-emergence of WNV in Northern Greece, indicating that Hungary remains an important ecological niche for the virus and has a central role for the dissemination of novel strains in the Balkans. In Northern Greece, tMRCA estimations indicated that a 1-to 2-year period of silent enzootic transmission precedes spread to dead-end hosts. Reconstruction of WNV population dynamics, from WGS data, revealed epidemic patterns characterized by 3- to 5-year oscillations in Europe. Future studies are necessary to determine the possible driving factors for these fluctuations i.e. avian herd immunity and climatic conditions affecting mosquito and bird populations. Maintaining adequate epidemiological surveillance with emphasis on obtaining WGS data, in areas at risk, is crucial for understanding the epidemiology and transmission patterns of WNV. It can further support integrated programs for risk assessment of virus circulation dynamics, aiming to targeted prevention and response measures for veterinary and public health in Europe.
西尼罗河病毒（WNV）是一种虫媒病毒，可导致人类和马属动物神经侵袭性疾病。自 2004 年以来，欧洲已鉴定出线粒体 2 型 WNV 株，并与严重疫情有关，其中 2018 年的疫情超过了前七年的总和。本研究旨在探讨塑造 2 型 WNV 株（属于中欧/匈牙利亚分支）遗传多样性的进化过程，并重建欧洲，特别是巴尔干半岛的起源和传播途径。为此，分析了大量全基因组序列（WGS），以及新鉴定的序列，包括 2018 年希腊 WNV 传播季节的菌株。最大似然和贝叶斯推断方法用于进行系统发育和系统发育动力学分析和系统地理学重建。大多数中欧/匈牙利 2 型菌株分为 2 个系统发育亚群（中欧/西南欧和巴尔干），具有布什状拓扑结构。净化选择塑造了它们的进化，但在 NS1、NS4B 和 NS5 的 7 个非结构蛋白密码子中发现了强烈的正选择证据。32 个氨基酸取代在不同的系统发育亚群中固定，表明随机遗传漂变是大多数进化变化的原因。病毒迁移，随后是局部进化，导致整个欧洲不断进化的菌株。总共支持了 10 次离散地理位置之间的病毒转移，涉及从中欧到其他地区的病毒传播。三起新的、独立的来自匈牙利和保加利亚的传入事件导致了 2018 年希腊北部 WNV 的再次出现，表明匈牙利仍然是该病毒的重要生态位，在巴尔干半岛传播新菌株方面发挥着核心作用。在希腊北部，tMRCA 估计表明，在传播到死胡同宿主之前，存在 1 到 2 年的沉默地方性传播期。从 WGS 数据重建 WNV 种群动态，揭示了欧洲具有 3 到 5 年波动的流行模式。未来的研究需要确定这些波动的可能驱动因素，即鸟类群体免疫和影响蚊子和鸟类种群的气候条件。在有风险的地区，通过强调获得 WGS 数据来维持适当的流行病学监测，对于了解 WNV 的流行病学和传播模式至关重要。它可以进一步支持针对病毒循环动态风险评估的综合计划，旨在针对欧洲兽医和公共卫生采取有针对性的预防和应对措施。
