Methods for Quantification of Viruses

Virus quantification is widely practised in both commercial and academic laboratories involved in research or production of viral vaccines, recombinant proteins, viral antigens, or antiviral agents. For this, the cell culture-based endpoint dilution assays are the most widely used methods. However, these infectivity assays are laborious, time consuming, and susceptible to failures due to the contamination of cells. With the advancement in science, a number of other methods based on chemical or physical principles have been developed for determining the viral load in a given sample. These methods include electron microscopy, hemagglutination assay, qPCR, flow cytometry, and serological assays such as ELISA. However, all of these methods have their own limitations and advantages associated with them and therefore one must be careful while selecting an appropriate method to determine the virus titer and interpretation of results. Here, we describe the theory and practical aspects of the most commonly used methods for virus quantification and their practical utility in the field of virology.