Diagnostic methods accurately identify virus in any patients or any sample. Effective clinical management of the disease is essential for controlling and limiting virus spread. Accurately identifying current or past infections is crucial for preventing transmission, administering appropriate treatment, and monitoring the progress of therapy.
Optical detection of virions by microscopy techniques:
- a) Electron microscopy (EM)
- b) Light microscopy
- c) Fluorescence microscopy
Modern techniques for the rapid diagnosis of viral infections:
- a) Nucleic Acid Amplification techniques (NAATs): PCR, qPCR, LAMP,NGS
- b) Quantitative virus assays: The plaque assay, HA-HI,
Quantitative Assay: Virus quantification is counting or calculating the number of virus particles (virions) in a sample to determine the virus concentration.
There are basically two types of viral quantification tests—physical & biological .
A. Physical/Chemical Methods of Virus Quantitation:
The second category of virus quantification assays relies on the chemical or physical measurement of virus particles. However, these methods cannot distinguish between infectious and non-infectious viral particles, meaning they can yield results even if the sample contains no infectious virus (Fox et al., 1995).
- Direct visualization of virions by electron microscopy (EM),direct & indirect immunofluorescence assay
- Hemagglutination (HA) assay
- Genome quantification by PCR
- Serological assays(ELISA)
- Flow cytometry or flow cytometry
B. Biological/Infectivity assays are the tests that measure virions that can successfully infect a cell to produce infectious progeny. The inactivated or non-infectious virion are not counted in such assays.
In infectivity assays, viruses are introduced to a monolayer of susceptible host cells, embryonated eggs, or animals to assess their ability to replicate. These assays evaluate the virus particles that can replicate in a specific cell type or animal.
There are two main types of biological/infectivity assays:
- a) Plaque assay and
- b) Quantal assays, also referred to as End-point dilution assays.