Development and optimization of a direct plaque assay for human and avian metapneumoviruses

► A direct plaque assay for hMPV and aMPV was developed. ► The direct plaque assay is highly sensitive and reliable. ► The direct plaque assay is easy, rapid, more convenient, more economical, and allowed for plaque purification. ► The direct plaque assay is a valuable method for quantitation and evaluation of the biological properties of metapneumoviruses.