Seroprevalence of avian influenza virus and its relationship with increased mortality and decreased egg production.

To evaluate the occurrence of avian influenza viruses (AIV) infections in southern Pakistan, an enzyme-linked immunosorbent assay was initially used to screen sera from broiler, layer and broiler breeder flocks for the presence of antibodies to type A influenza viruses. Data from this survey showed high levels of AIV antibodies, indicating unrecognized AIV infection occurring in these flocks. Based on this information a second investigation was undertaken in selected broiler-breeder, broiler and layer flocks. In this investigation, nine H9N2 AIV isolates were recovered. Serological data from this investigation indicated that chickens in flocks with a previous history of respiratory tract infection and some without overt clinical respiratory signs had seroconverted to H9N2 AIV.