PDF(Pubmed)
Abstract：
Swine influenza A virus (swIAV) is one of the main viral pathogens responsible for respiratory disease in farmed pigs. While outbreaks are often epidemic in nature, increasing reports suggest that continuous, endemic infection of herds is now common. The move towards larger herd sizes and increased intensification in the commercial pig industry may promote endemic infection; however, the impact that intensification has on swIAV infection dynamics and evolution is unclear. We carried out a longitudinal surveillance study for over 18 months on two enzootically infected, intensive, indoor, and multi-site pig production flows. Frequent sampling of all production stages using individual and group sampling methods was performed, followed by virological and immunological testing and whole-genome sequencing. We identified weaned pigs between 4 and 12-weeks old as the main reservoir of swIAV in the production flows, with continuous, year-round infection. Despite the continuous nature of viral circulation, infection levels were not uniform, with increasing exposure at the herd level associated with reduced viral prevalence followed by subsequent rebound infection. A single virus subtype was maintained on each farm for the entire duration of the study. Viral evolution was characterised by long periods of stasis punctuated by periods of rapid change coinciding with increasing exposure within the herd. An accumulation of mutations in the surface glycoproteins consistent with antigenic drift was observed, in addition to amino acid substitutions in the internal gene products as well as reassortment exchange of internal gene segments from newly introduced strains. These data demonstrate that long-term, continuous infection of herds with a single subtype is possible and document the evolutionary mechanisms utilised to achieve this.
摘要：
猪甲型流感病毒（swIAV）是导致养殖猪呼吸道疾病的主要病毒病原体之一。虽然疫情通常是流行病，越来越多的报告表明，牛群的地方性感染现在很常见。商业养猪业向更大的畜群规模和更高的集约化发展可能会促进地方性感染；然而，强化对swIAV感染动态和演变的影响尚不清楚.我们进行了为期18个月的纵向监测研究，密集，室内,和多地点生猪生产流动。采用个别抽样和整群抽样方法对所有生产阶段进行频繁抽样，其次是病毒学和免疫学测试和全基因组测序。我们将4至12周龄的断奶猪确定为生产流中的主要SwIAV库，连续的,全年感染。尽管病毒循环具有连续性，感染水平不一致，随着人群暴露的增加，病毒流行率降低，随后反弹感染。在整个研究期间,在每个农场维持单一病毒亚型。病毒进化的特征是长时间的停滞，而快速变化的时期与牛群内暴露的增加相吻合。观察到与抗原漂移一致的表面糖蛋白突变的积累，除了内部基因产物中的氨基酸取代以及新引入菌株的内部基因片段的重配交换。这些数据表明，从长远来看，用单一亚型连续感染牛群是可能的，并记录了实现这一目标的进化机制。
