Improved Zika virus plaque assay using Vero/TMPRSS2 cell line

While there are several methods of viral quantification, the plaque assay remains the gold standard for accurate quantification of replication-competent, cytopathic viruses including Zika virus (ZIKV). Vero cells are commonly used to titer ZIKV stock via the plaque assay. Prior to the initiation of this study, we observed that ZIKV-PRV strain plaque assays using Vero cells often yielded plaques that were very small, overly diffuse, and hard to count. We also observed that the ZIKV-CAM strain often did not produce plaques at all on Vero cells. This study shows that Vero cells expressing TMPRSS2 improve the morphology and visibility of plaques produced by ZIKV-PRV and ZIKV-CAM compared to regular Vero cells and may, therefore, be a better alternative to use for performing plaque assays for these strains and perhaps for other strains of ZIKV that are difficult to titer. However, Vero cells proved to be superior for generating high titer stock.