Influenza A subtype diversity in fall migrating teal: almost a decade in the making

Wild birds in the order Anseriformes are important reservoirs for influenza type A viruses (IAV); however in wild birds, IAV prevalence and subtype diversity vary greatly by location, season, and species. To better understand... [ view full abstract ]

Wild birds in the order Anseriformes are important reservoirs for influenza type A viruses (IAV); however in wild birds, IAV prevalence and subtype diversity vary greatly by location, season, and species. To better understand the ecology of IAV during the early fall migration (September) of teal through the Gulf Coast of the United States (Louisiana and Texas), surveillance of blue-winged (Anas discors) and green-winged (Anas carolinensis) teal was conducted annually from 2007-2015. Overall, 551 low pathogenicity (LP) IAV were recovered from cloacal swabs taken from hunter-acquired teal representing a prevalence of 7.6% (range: 0.4%-23.9%) for the 9-year period. All relevant North American “duck” HA (1-12, 14) and NA (1-9) subtypes were isolated from this collection. Consistent with historic results from fall migrating ducks, H3 and H4 subtypes were most common; however, this diversity is in contrast to the documented predominance of LP H7 viruses in teal in this region during their spring migration. Interestingly, during the fall, annual subtype turnover was not observed with viruses in the H4 subtype predominating in every year. Furthermore, the N6 and N8 subtypes which were usually associated with H4 were most common during fall migration, with N6 predominating in all but one year; these NA subtypes have not been recovered in this area in the spring. Ongoing annual surveillance efforts will continue to inform our understanding of IAV prevalence and diversity in these long-distant migrants, as well as provide a better understanding of the potential effects of population immunity as related to these unique seasonal patterns.