Determination of a Suitable Avian Cell Line for the Quantification of Avian Reovirus via Plaque Assays

Avian reovirus (ARV) infections pose a significant economic threat to poultry production despite biocontainment and routine vaccination efforts. Quantifying ARV load is essential for understanding infection dynamics. There is a widespread misperception that ARVs in cultures do not produce countable plaques, leading most in the field to use the less useful 50% tissue culture infectious dose quantifications. Here, we compare the suitability of two well-known avian cell lines, quail myoblast clone 5 (QM5) and leghorn male hepatocellular carcinoma (LMH), for use in plaque assays for the quantification of ARV. LMH cells, which exhibit syncytia formation postinfection, proved unsuitable for plaque assays due to poor substrate adherence, the tendency to form syncytia-like conglomerations of cells even when uninfected, and the tendency for areas of the substrate cleared by viral cytopathic effect (CPE) to quickly fill in with new cell growth. In contrast, QM5 cells demonstrated clear contact inhibition and well-defined CPE, enabling distinct, countable plaques even at high virus titers. Therefore, although LMH cells are advantageous for viral propagation, QM5 cells are better suited for plaque assays to assess ARV infectivity, with QM5 enabling more precise viral growth tracking and quantification.