Knowledge Bank

Wild waterfowl are the primary natural reservoirs of influenza A virus (IAV), the causative agent of avian, swine, and human influenzas. Type A influenza viruses are subtyped using two glycoproteins, hemagglutinin (HA) and neuraminidase (NA) of which there are 16 HA and 9 NA circulating in waterfowl. A cursory data review indicated differences in IAV recovery between waterfowl species. Here, IAV recovery was compared in mallard ducks (Anas platyrhynchos) and northern shoveler ducks (Anas clypeata) due to similar wintering grounds, but differences in eating patterns. We hypothesized that IAV prevalence and subtype diversity would be different between the two identified waterfowl species. Data for this study came from IAV surveillance conducted 2008-2015 in hunter-harvested waterfowl along the Mississippi Migratory Bird Flyway. IAV prevalence, dominant viral subtypes overall, and predominant subtypes based on migratory period were examined between the waterfowl species. A total of 7,398 cloacal swabs were collected from mallards, resulting in 509 (6.9%) IAV isolates representing 12 HA and 9 NA subtypes. From northern shovelers, 104 (5.8%) IAVs representing 13 HA and 9 NA subtypes were isolated from 1,779 samples. No significant difference in the IAV prevalence was found between host species, but the predominant subtypes among the species were different. The predominant subtypes in mallards were found to be H4 and N8 whereas in northern shovelers the predominant subtypes were H7 and N3. Subtype H7 has caused highly pathogenic avian influenza (HPAI) outbreaks in poultry. As a result, additional surveillance of IAV in northern shovelers needs to be conducted, ideally throughout the year and across latitudes, to determine if the species predilection for H7 is significant. The IAV subtype diversity found validates the need for continued surveillance in both waterfowl species.