Résumé
Two hundred thirty specimens of wild birds were collected from some areas in Heilongjiang Province during the period of 2003~2004, including two batches of specimens collected randomly from a same flock of mallards in Zhalong Natural Reserve in August and December, 2004, respectively. Primary virus isolation and identification for avian influenza virus (AIV) and Newcastle disease virus (NDV) were performed. The results showed that only two specimens of young mallards collected from Zhalong Natural Reserve in August, 2004 were positive to AIV (isolation rate 0.9%), and one strain (D57) of these two virus isolates was identified to be H9 subtype by hemagglutination inhibition test. Meanwhile, the two batches of blood serum samples of mallards from Zhalong were also examined for antibodies against AIV and NDV. Among 38 blood serum samples collected in August, antibodies against the hemagglutinin of H1, H3, H5, H6 and H9 subtypes of AIV were found in 1, 0, 2, 0 and 8 samples, respectively; and 11 samples were found with antibody against NDV. Whereas the NDV isolation in both two batches of specimens of mallard was negative, all of the 32 blood serum samples collected in December were negative for antibodies against AIV and NDV.