Abstract
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.
Highlights
Water-borne transmission of influenza A (IA) viruses has been suggested as an important transmission mechanism in wild and domestic duck populations [1,2]
Influenza A virus prevalence in duck populations Based on IA virus isolation, the prevalence of infected waterfowl was 13.165.8% and 9.961.2% in 2006 and 2007, respectively
All ducks inoculated with A/Surface water/Minnesota/NW1-T/2006 (H4N6) tested positive for IA antibody from day 4 until the end of the experiment. Both the H3N8 and H4N6 subtypes that were isolated from surface lake water have been commonly detected in North American waterfowl [24]. The prevalence of these subtypes was relatively low in wild duck populations during the years of detection; the limited number of viruses recovered during 2006 provided limited information on virus subtypes circulating in local duck populations during that year
Summary
Water-borne transmission of influenza A (IA) viruses has been suggested as an important transmission mechanism in wild and domestic duck populations [1,2]. Viral persistence in aquatic habitats has been demonstrated to be a determinant for IA virus transmission dynamics in wild duck populations [13,14,15]. Several studies have attempted to isolate or detect IA viruses from surface water in habitats utilized by waterfowl [16,17,18,19,20,21,22] In these studies, virus subtypes detected in local aquatic habitats reflected the current subtype diversity circulating in waterfowl populations. Environmental persistence and replication in the natural host have not been documented for water-isolated viruses, limiting our understanding of viral fitness in ducks and aquatic habitats
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