Biological characterization of FPV, Ulster 73, replicative cycle.

The replication of an avian influenza A, Fowl plague virus (FPV), Ulster 73 strain, was studied in chick embryo fibroblasts, assumed to be the natural host, and in cells of different origin such as LLC-MK2, Hep-2, Vero, KB and Mc Coy. In the natural host, FPV shows a characteristic pattern of polypeptide synthesis suggesting a transcriptional and/or translational mediated control mechanism, specific for this strain of influenza A. FPV was able to give a productive infection in all the above mentioned cells releasing mature viral particles. This behaviour is very interesting if one compares FPV, Ulster strain to FPV, Rostock strain. These viruses, belonging to the same antigenic subtype (H7 N1 group) recognize the same cellular determinants but Rostock strain undergoes an abortive replication whereas Ulster strain gives productive infection in all cellular lines tested. These observations lead to postulate a viral genetic mechanism controlling host range both at early and late steps in infection. This genetic mechanism controls the interaction between viral and cell molecules affecting synthesis of virus specific polypeptides.