Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Viral titer is the concentration of virus particles in a sample, typically expressed as plaque-forming units per milliliter (PFU/mL). It is an essential measure in virology to assess viral infectivity and replication.
5 Must Know Facts For Your Next Test
Viral titers are commonly measured using plaque assays, which involve infecting a monolayer of host cells and counting the resulting plaques.
High viral titers indicate a high concentration of infectious virus particles, while low titers suggest fewer infectious particles.
Accurate determination of viral titer is critical for vaccine production, antiviral drug testing, and basic virology research.
Other methods to determine viral titer include endpoint dilution assays and quantitative PCR (qPCR), though qPCR measures genetic material rather than infectious particles.
Standardization and proper controls are essential when measuring viral titers to ensure reproducibility and accuracy.
A method used to measure the number of virus particles capable of forming plaques per unit volume.
Endpoint Dilution Assay: A technique used to estimate the concentration of viruses by serially diluting a sample until no infection occurs.
Quantitative PCR (qPCR): A molecular biology technique that quantifies DNA or RNA sequences, often used to estimate virus load but not directly measuring infectivity.