Southeastern Cooperative Wildlife Disease Study, Department of Population Health, College of Veterinary Medicine, University of Georgia, Athens, Georgia, United States of America.
PLoS One. 2011;6(10):e26566. doi: 10.1371/journal.pone.0026566. Epub 2011 Oct 20.
Water-borne transmission has been suggested as an important transmission mechanism for Influenza A (IA) viruses in wild duck populations; however, relatively few studies have attempted to detect IA viruses from aquatic habitats. Water-isolated viruses have rarely been genetically characterized and evaluation for persistence in water and infectivity in natural hosts has never been documented. In this study, we focused on two IA viruses (H3N8 and H4N6 subtypes) isolated from surface lake water in Minnesota, USA. We investigated the relative prevalence of the two virus subtypes in wild duck populations at the sampling site and their genetic relatedness to IA viruses isolated in wild waterbirds in North America. Viral persistence under different laboratory conditions (temperature and pH) and replication in experimentally infected Mallards (Anas platyrhynchos) were also characterized. Both viruses were the most prevalent subtype one year following their isolation in lake water. The viruses persisted in water for an extended time period at constant temperature (several weeks) but infectivity rapidly reduced under multiple freeze-thaw cycles. Furthermore, the two isolates efficiently replicated in Mallards. The complete genome characterization supported that these isolates originated from genetic reassortments with other IA viruses circulating in wild duck populations during the year of sampling. Based on phylogenetic analyses, we couldn't identify genetically similar viruses in duck populations in the years following their isolation from lake water. Our study supports the role for water-borne transmission for IA viruses but also highlights that additional field and experimental studies are required to support inter-annual persistence in aquatic habitats.
水传播已被认为是野鸭种群中甲型流感（IA）病毒的重要传播机制；然而，很少有研究试图从水生栖息地检测到 IA 病毒。从水生环境中分离出的病毒很少进行基因特征分析，也从未有研究评估其在水中的持久性和对自然宿主的感染性。在本研究中，我们专注于从美国明尼苏达州的湖泊表面水中分离出的两种 IA 病毒（H3N8 和 H4N6 亚型）。我们调查了在采样点的野鸭种群中这两种病毒亚型的相对流行率，以及它们与在北美的野生水禽中分离出的 IA 病毒的遗传关系。我们还研究了两种病毒在不同实验室条件（温度和 pH 值）下的持久性以及在实验感染的绿头鸭（Anas platyrhynchos）中的复制情况。这两种病毒在其从湖水中分离出来后的一年中是最流行的亚型。病毒在恒定温度下（数周）可以在水中长时间持续存在，但在多次冻融循环下感染性迅速降低。此外，这两种分离株在绿头鸭中高效复制。完整基因组特征分析支持这些分离株起源于与当年采样期间在野鸭种群中循环的其他 IA 病毒的基因重组。基于系统进化分析，我们无法在其从湖水分离出来的几年后在鸭群中鉴定出具有遗传相似性的病毒。我们的研究支持了水传播在 IA 病毒中的作用，但也强调需要进行更多的野外和实验研究来支持其在水生环境中的年度持久性。
