<prompt> Test for quantification of viral infectivity isCytopathic effectPlaque assayElectron microscopyHaemagglutination  <response>: Viral assaysVirus content of a specimen can be assayed in two ways1. With reference to total virus particles-Electron microscopyHemagglutination2. With reference to the infectious virions onlyA. Quantal Assays Indicates the presence or absence of infectious virus e.gDeath of the experimental animal.Production of haemagglutinin in allantoic fluid.Appearance of cytopathological effects on cell cultures.B. Quantitative infective assayIt measures the exact number of infectious particles. Eg:Plaque assay monolayer cell culture CAM.Pock assay on chick embryo chorioallantoic membrane. Viruses producing pocks on chorioallantoic membrane are HSV, vaccinia, smallpox variola, monkey pox, cowpox and camel pox. 