Test for quantification of viral infectivity is
Viral assays

Virus content of a specimen can be assayed in two ways

1. With reference to total virus particles-

Electron microscopy
Hemagglutination

2. With reference to the infectious virions only
A. Quantal Assays
→ Indicates the presence or absence of infectious virus e.g

Death of the experimental animal.
Production of haemagglutinin in allantoic fluid.
Appearance of cytopathological effects on cell cultures.

B. Quantitative infective assay

It 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.
Cytopathic effect
Plaque assay
Electron microscopy
Haemagglutination