The prevalence of influenza A virus infection, and the distribution of different subtypes of the virus, were studied in 604 geese and ducks shot during ordinary hunting 2005. The study was based upon molecular screening of cloacal swabs taken by the hunters. The sampling included the following species: greylag (Anser anser), mallard (Anas platyrhynchos), wigeon (Anas penelope), teal (Anas crecca), goosander (Mergus merganser), tufted duck (Aythya fuligula), common scoter (Melanitta nigra), goldeneye (Bucephala clangula), and red-breasted merganser (Mergus serrator).
The samples found to be positive in the initial pan-influenza A virus reverse transcription-polymerase chain reaction (RT-PCR) were further subtyped by using a specific H5 RT-PCR and full-length RT-PCRs for the hemagglutinin (HA) and neuraminidase genes.
None of the greylag samples (0/185) were positive for influenza A virus, whereas 19.1% of the ducks (80/419) were positive. The prevalences of influenza A virus in the different duck species were as follows: mallard, 20.4% (58/284); wigeon, 12.5% (8/64); teal, 30.9% (13/42); goosander, 0% (0/5); tufted duck, 0% (0/4); common scoter, 14.3% (1/7); goldeneye, 0% (0/11); and red-breasted merganser, 0% (0/2). H5N1 subtype was found in one mallard and H5N2 subtype in another mallard and one teal. Sequencing of the HA gene identified all three viruses as low-pathogenic strains, closely related to low-pathogenic H5 influenza A viruses evidenced in recent years in Sweden and the Netherlands. The other subtypes identified included H1N1, H2, H3N2, H3N8, H6N1, H6N2, H6N8, H8N4, H9N2, H11N9, and H12 in mallards; H3N2, H6N2, H6N8, and H9N2 in teals; and H6N2 in wigeons and common scoter.