Surveillance studies in wild animals provide information on the prevalence of avian influenza viruses in the environment, and enables banking of reference reagents and putative vaccine strains to be used in times of outbreaks in humans and animals. In the past five years we have performed surveillance studies in wild birds primarily in The Netherlands and Sweden. In ducks, geese and gulls the prevalence of influenza A virus ranged from 0 to 60 percent, depending on bird species, location and

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... son. The detection of avian influenza A viruses in other bird species was rare. Most of the fifteen haemagglutinin subtypes and all nine neuraminidase subtypes described to date were found in birds in Northern Europe. In addition, we have identified a novel haemagglutinin subtype(H16) in black-headed gulls. Viruses of subtypes H5 and H7 were found less frequently than other subtypes, and were closely related to the H5 and H7 highly pathogenic avian influenza viruses that have caused outbreaks in poultry in Italy and The Netherlands between 1997 and 2003.