Pock Forming Unit

**Semantic type:** Quantitative Concept

**Definition:** A measure of viable infectious entities (e.g. viral particles or group of particles) in the specimen or product defined as the smallest quantity of a viral suspension that can produce a cytopathic effect in the host chick chorio-allantoic membrane challenged with the defined inoculum, visible under the microscope and/or to the naked eye as a pock.

**Synonyms:** - pock forming unit - pock forming unit(s)