Overview of diagnostic methods  

In general, diagnostic tests can be grouped into 3 categories.: (1) direct detection, (2) indirect examination (virus isolation), and (3) serology. In direct examination, the clinical specimen is examined directly for the presence of virus particles, virus antigen or viral nucleic acids. In indirect examination, the specimen into cell culture, eggs or animals in an attempt to grow the virus: this is called virus isolation. Serology actually constitute by far the bulk of the work of any virology laboratory. A serological diagnosis can be made by the detection of rising titres of antibody between acute and convalescent stages of infection, or the detection of IgM. In general, the majority of common viral infections can be diagnosed by serology. The specimen used for direction detection and virus isolation is very important. A positive result from the site of disease would be of much greater diagnostic significance than those from other sites. For example, in the case of herpes simplex encephalitis, a positive result from the CSF or the brain would be much greater significance than a positive result from an oral ulcer, since reactivation of oral herpes is common during times of stress.  

1. Direct Examination of Specimen

1. Electron Microscopy morphology / immune electron microscopy

2. Light microscopy histological appearance - e.g. inclusion bodies

3. Antigen detection immunofluorescence, ELISA etc.

4. Molecular techniques for the direct detection of viral genomes    

2. Indirect Examination

1. Cell Culture - cytopathic effect, haemadsorption, confirmation by neutralization, interference,  immunofluorescence etc.

2. Eggs pocks on CAM - haemagglutination, inclusion bodies

3. Animals disease or death confirmation by neutralization    

3. Serology

Detection of rising titres of antibody between acute and convalescent stages of infection, or the detection of IgM in primary infection.  

Classical Techniques	Newer Techniques
1. Complement fixation tests (CFT)	1. Radioimmunoassay (RIA)
2. Haemagglutination inhibition tests	2. Enzyme linked immunosorbent assay (EIA)
3. Immunofluorescence techniques (IF)	3. Particle agglutination
4. Neutralization tests	4. Western Blot (WB)
5. Single Radial Haemolysis	5. Recombinant immunoblot assay (RIBA), line immunoassay (Liatek) etc.