A virulent strain of deformed wing virus (DWV) of honeybees (Apis mellifera) prevails after Varroa destructor-mediated, or in vitro, transmission.
A virulent strain of deformed wing virus (DWV) of honeybees (Apis mellifera) prevails after Varroa destructor-mediated, or in vitro, transmission.
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DOI：
10.1371/journal.ppat.1004230
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发表时间：
2014-06
期刊：
影响因子：
6.7
通讯作者：
Evans DJ
中科院分区：
文献类型：
--
作者：
Ryabov EV;Wood GR;Fannon JM;Moore JD;Bull JC;Chandler D;Mead A;Burroughs N;Evans DJ
全球分布的外寄生虫狄斯瓦螨是西方蜜蜂（Apis mellifera）的病毒病原体，特别是黄病毒畸形翅病毒（DWV）的载体。在没有瓦螨属低水平DWV的情况下发生，通常引起无症状感染。相反，瓦螨属感染的菌落显示病毒水平显著升高，越冬菌落损失增加，蛹发育受损和有症状的工蜂。为了确定病毒种群的变化是否是由于瓦螨属扩增和引入强毒病毒株和/或抑制宿主免疫应答所致，我们将瓦螨属未处理幼虫暴露于口服和瓦螨属传播的DWV。我们监测了病毒水平和多样性在发展脓和相关的瓦螨属，所产生的RNAi反应和转录组的变化，在主机。根据瓦螨属相关性（存在/不存在）和病毒水平（低/高）将暴露的脓毒症分为三组。无瓦螨蛹均表现出低水平的高度多样化DWV种群，经口暴露的蛹（NV组）表现出种群组成的变化。瓦螨相关脓毒症表现出低水平的不同DWV群体（VL组）或高水平的DWV近克隆毒性变体（VH组）。这些组和未暴露的对照组（C）也可以通过观察到的转录组变化的主成分分析来区分，其中包括参与发育和免疫应答的几个基因。所有检测的瓦螨属均含有多样化的复制型DWV群体，这意味着VH组中存在的毒性变体，并且在时间和地理上分离的瓦螨属侵染菌落的RNA-seq分析中占主导地位，是在从瓦螨属传播后选择的，这一结论得到了混合病毒群体体外直接注射腐殖酸的支持。DWV的毒性变体的鉴定、瓦螨属在其传播中的作用以及由此产生的宿主转录组变化进一步加深了我们对蜜蜂的这种重要病毒病原体的理解。蜜蜂是最重要的人工授粉昆虫，每年为全球农业生产贡献数十亿美元。在上个世纪，一种寄生螨，瓦螨，已经在世界范围内传播，由于其在以蜜蜂“血液”为食时传播病毒混合物，对蜂群健康产生重大影响。对蜂群健康最重要的病毒是畸形翅病毒（DWV），高水平的DWV会导致发育畸形和过早衰老，导致越冬蜂群的大量损失。在对个体瓦螨属暴露脓疱的实验中，我们证明了单一类型的毒性DWV在受体脓疱中扩增1，000 - 10，000倍，尽管螨含有高度多样性的复制DWV菌株。我们可以通过直接注射带有混合病毒种群的脓液来概括这一点，表明强毒株通过传播途径传播。同时，我们检测到蜜蜂的免疫反应和发育基因表达的变化，并提出这些有助于DWV的特征性发病机制。DWV强毒株的鉴定对于改善蜂群健康的治疗性或预防性干预具有意义，并且有助于我们对这种重要的蜜蜂病毒病原体的生物学的理解。
The globally distributed ectoparasite Varroa destructor is a vector for viral pathogens of the Western honeybee (Apis mellifera), in particular the Iflavirus Deformed Wing Virus (DWV). In the absence of Varroa low levels DWV occur, generally causing asymptomatic infections. Conversely, Varroa-infested colonies show markedly elevated virus levels, increased overwintering colony losses, with impairment of pupal development and symptomatic workers. To determine whether changes in the virus population were due Varroa amplifying and introducing virulent virus strains and/or suppressing the host immune responses, we exposed Varroa-naïve larvae to oral and Varroa-transmitted DWV. We monitored virus levels and diversity in developing pupae and associated Varroa, the resulting RNAi response and transcriptome changes in the host. Exposed pupae were stratified by Varroa association (presence/absence) and virus levels (low/high) into three groups. Varroa-free pupae all exhibited low levels of a highly diverse DWV population, with those exposed per os (group NV) exhibiting changes in the population composition. Varroa-associated pupae exhibited either low levels of a diverse DWV population (group VL) or high levels of a near-clonal virulent variant of DWV (group VH). These groups and unexposed controls (C) could be also discriminated by principal component analysis of the transcriptome changes observed, which included several genes involved in development and the immune response. All Varroa tested contained a diverse replicating DWV population implying the virulent variant present in group VH, and predominating in RNA-seq analysis of temporally and geographically separate Varroa-infested colonies, was selected upon transmission from Varroa, a conclusion supported by direct injection of pupae in vitro with mixed virus populations. Identification of a virulent variant of DWV, the role of Varroa in its transmission and the resulting host transcriptome changes furthers our understanding of this important viral pathogen of honeybees. Honeybees are the most important managed pollinating insect, contributing billions of dollars to annual global agricultural production. Over the last century a parasitic mite, Varroa, has spread worldwide, with significant impacts on honeybee colony health as a consequence of its transmission of a cocktail of viruses while feeding on honeybee ‘blood’. The most important virus for colony health is deformed wing virus (DWV), high levels of which cause developmental deformities and premature ageing resulting in high overwintering colony losses. In experiments on individual Varroa-exposed pupae we demonstrate that a single type of virulent DWV is amplified 1,000–10,000 times in the recipient pupae, despite the mite containing a high diversity of replicating DWV strains. We could recapitulate this by direct injection of pupae with mixed virus populations, showing the virulent strain is advantaged by the route of transmission. In parallel, we detected changes in the immune response and developmental gene expression of the honeybee and propose that these contribute to the characteristic pathogenesis of DWV. Identification of a virulent strain of DWV has implications for therapeutic or prophylactic interventions to improve honeybee colony health, as well as contributing to our understanding of the biology of this important honeybee viral pathogen.
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