Circulation of influenza viruses in wild waterfowl wintering in Italy during the 1993-99 period: evidence of virus shedding and seroconversion in wild ducks.

The mechanisms of perpetuation of influenza A viruses in aquatic birds, their main reservoir in nature, have not yet been completely clarified. One hypothesis is that they continue to circulate in waterfowl throughout the year, even though virus isolations during the winter months are rare. We analyzed influenza virus circulation in wild ducks in Italy during six winter seasons (1993-99), using virus isolations and serological analyses.