Diagnostic Methods of Viruses : Direct and Indirect Examination of Specimen

Diagnostic Methods of Viruses

Tests can be grouped into 3 categories

1. Direct examination of specimen

A. Light microscopy histological appearance e.g. inclusion bodies
B. Antigen detection immunofluoreicence, ELISA etc
C. Molecular techniques for the direct detection of viral genomes
D. Electron microscopy (not applicable in health centers)

1. Indirect examination

a. Cell culture – cytopathic effect, hemadsorption, confirmation by neutralization, interference, immunofluorescence etc.

b. Animals disease or death confirmation by neutralization

c. Serology; detection of antibody and convalescent stages of infection, or the detection of IgM in primary infection.

Direct examination of specimen

o Fluoresce in an enzyme or a radiolabel (the indicator system) is conjugated to the antibody used to detect the virus (Primary antibody) specifically.


1. Antigen -capture EIA, which is used to detect extra cellular viral antigens in exudates and homogenized tissues. A common application of antigen capture, for which several commercial kits are available, is in the diagnosis of Herpes simplex.

2. Immuno fluorescence (IF) for the detection of infected cells in exudates and secretions

3. Immuno filtration is a powerful technique for rapid detection of infected cells in tissue samples

4. Detection for viral DNA or RNA sequences in clinical samples.

For rapid diagnostic purposes, virus-specific nucleic acid sequences in serum, cells or tissue extracts are detected primarily by dot- blot hybridization techniques.

Polymerase Chain Reaction is important for virus diagnosis.

It is extremely sensitive and widely regarded as a research tool with limited application to the diagnostic workbench.

Indirect examination

o The indicator system is conjugated to a secondary antibody, which in turn directed against the primary antibody.

The indirect method can be constructed to react with human IgG or IgM molecules use in antibody assays

o The major indicator systems include immunofluorescence assay (FA), enzyme immunoassay (EIA), and radioimmunoassay (RIA)

Ex. The EIA procedure can be adapted to perform:

i. An enzyme linked immunosorbent assay (ELISA) where on unlabelled antibody (the capture antibody) is bound to a solid phase (e.g., a latex bead or the bottom of a micro titer plate well)

to “capture” the antigen and a second enzyme- labeled antibody is added to detect the captured antigen ii. Immunoperoxidase (IP) methods to demonstrate specific viral antigen by light microscopy in tissues from biopsy or autopsy specimens or cells form viral cell cultures.

Serologic Methods – detection of rising titers of antibody between acute & convalescent stages of infection

-Measurement of IgG antiviral antibodies is used to determine immunity, while quantization of IgG or IgM antibodies can diagnose current or recent infection. Generally IgM antibodies denote a new or recent infection.

-Classical techniques which measure only IgG or ‘total” antibodies

o Neutralization tests
o Complement fixation (CF)
o Hemaglutination inhibitation (HI)
Newer techniques, which are modified to detect either IgG or IgM are;
o Immunofluorescent Assay (FA)
o Enzyme linked immunosorbent assay (EIA)

Thanks For Visiting ! Keep Your Healthy !

Diagnostic Methods of Viruses : Direct and Indirect Examination of Specimen 2018-12-26T01:08:00-08:00 Rating: 4.5 Diposkan Oleh: David Maharoni