Low pathogenic avian influenza viruses in wild migratory waterfowl in a region of high poultry production, Delmarva, Maryland

Migratory waterfowl are natural reservoirs for low pathogenic avian influenza viruses (AIVs) and may contribute to the long-distance dispersal of these pathogens as well as spillover into domestic bird populations. Surveillance for AIVs is critical to assessing risks for potential spread of these viruses among wild and domestic bird populations. The Delmarva Peninsula on the east coast of the United States is both a key convergence point for migratory Atlantic waterfowl populations and a region with high poultry production (>4,700 poultry meat facilities). Sampling of key migratory waterfowl species occurred at 20 locations throughout the Delmarva Peninsula in fall and winter of 2013–14. Samples were collected from 400 hunter-harvested or live-caught birds via cloacal and oropharyngeal swabs. Fourteen of the 400 (3.5%) birds sampled tested positive for the AIV matrix gene using real-time reverse transcriptase PCR, all from five dabbling duck species. Further characterization of the 14 viral isolates identified two hemagglutinin (H3 and H4) and four neuraminidase (N2, N6, N8, and N9) subtypes, which were consistent with isolates reported in the Influenza Research Database for this region. Three of 14 isolates contained multiple HA or NA subtypes. This study adds to the limited baseline information available for AIVs in migratory waterfowl populations on the Delmarva Peninsula, particularly prior to the highly pathogenic AIV A(H5N8) and A(H5N2) introductions to the United States in late 2014.