Lab Diagnosis of Viral Diseases: Five Approaches

By Acharya Tankeshwar •  Updated: 05/04/22 •  3 min read

The diagnosis of a viral infection can be established in several ways, often used together, namely:

  1. Detection of virus particles in a specimen taken from the appropriate site.
  2. Detection of viral antigens (Ag) in blood or body fluids
  3. Serological procedure to detect specific anti-viral antibodies (rise in antibody titre or presence of IgM antibody) or detection of the presence of cell-mediated immune response.
  4. Detection of viral nucleic acids in the blood or body cells of a patient
  5. Culture of infectious virus from an appropriate clinical specimen.
  6. Cytological or histological examination of cells from the site of the infection in those viral infections in which a characteristic viral cytopathic effect (CPE) is produced.

Microscopic identification of Viruses

Viruses can be detected and identified by direct microscopic examination of clinical specimens such as biopsy materials or skin lesions. Three different microscopy techniques are currently in use:

Serological procedure for the laboratory diagnosis of Viruses

Different Serological methods that can be used for viral infection diagnosis
Different Serological methods that can be used for viral infection diagnosis

Detection of Viral Antigens

Various tests such as ELISA, EFA etc can be done to detect the presence of viral antigens in the patient blood or biopsy materials. For the diagnosis of Hepatitis virus infection, HBsAg (Hepatitis viral surface antigen) or HBeAg (Hepatitis virus e antigens) can be detected. Similarly, detection of p24 viral antigen is the diagnostic method in case of HIV Infection.

Detection of Viral Nucleic acids

Detection of viral nucleic acids is one of the sensitive and rapid methods for laboratory diagnosis. It requires the use of PCR (polymerase chain reaction) to amplify the viral genome present in the sample and detection of the specific gene sequence of that particular virus by the use of a specific primer (while performing PCR) and probe (while detecting the specific sequence).  RNA viral assay is currently in use to monitor the course of HIV infection and to evaluate the patient progress.

Identification of the virus in the cell culture

Viruses are obligate intracellular parasites so we cannot grow them in ordinary media (like we grow bacteria, fungi) and require living cells for the growth and propagation.  The growth of the virus in the cell culture may produce a characteristic cytopathic effect (CPE) which helps us for presumptive diagnosis. If that particular virus does not produce the cytopathic effect, its presence can be detected by several other techniques such as Immunofluorescence assay (eg. DFA, IFA), Radioimmunoassay (RIA), Hemadsorption, decrease in acid production of infected cells, ELISA, Complement fixation, Hemagglutination inhibition method, neutralization, etc.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please email at microbeonline@gmail.com