Determination of infectivity of transforming avian sarcoma virus and parotitis virus in fibrin-embedded monolayer cultures.

A sensitive and reproducible technique for titration of transforming avian sarcoma virus, Rous sarcoma virus (RSV), in chick embryo cell monolayers embedded between two layers of a solid fibrin coagulum was developed. The foci of RSV-transformed fibrinolysis-exhibiting cells locally attacked the surrounding fibrin and were identifiable as plaque-like cell-free areas of retraction easily scored against the background of cells stained with neutral red. In comparison to the conventional assay in agar, the assay in fibrin proved more sensitive and less time-consuming. The titration technique in fibrin was also used for plaquing a cytopathogenic virus, parotitis virus, but the titration by conventional plaque assay in agar and the technique in fibrin yielded similar results in this case.