You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Test for quantification of viral infectivity is and explain in detail?
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.