Detection of virus growth in cell culture:
Virus growth in cell cultures is recognized by the development of cytopathic effect, haemadsorption, immune-fluorescence, electron microscopy and detection of enzymes.
- Cytopathic effects (CPE): CPE are morphological changes in the viral culture cell which was normal before viral inoculation. The viruses causing CPE are called cytopathogenic virus. The CPE produced by particular group of virus is specific. CPE includes:
- Lysis
- swelling
- fusion (syncytism)
- degranulation
- plaque formation
- lesion
Inclusion bodies:
These are granulated intracellular bodies produced by the host cell in response to some viral infection. These are confined within the cytoplasm (intracytoplasmic- rabies virus) or nucleus (intranuclear- herpes, adeno, measles viruses) and do not come out of cell. These are either basophilic or acidophilic. IBs formed by different viruses show distinct shape, size, location and staining properties. Some of the common IBs of viruses are:
- Negribody (rabies – detected after death)
- Liptshuty body (coronavirus)
- Councilman body (herpes virus)
- Guarneri body (ebola virus)
- Cowdary body (human herpes virus)
- Molluscum body (pox virus)
Fig: IB: Negri bodies in neurons in case of rabies.
Importance of IBs:
- Used in diagnosis of a viral disease.
- Helps in the identification of virus.
2. Haemadsorption: this is observed with haemagglutinating viruses (orthomixo, paramixo, toga viruses). Guinea pig erythrocytes added to virus infected tissue cultures adhere to the infected cells.
3. Immunufluorescence: viruses can be detected in infected cells by antiviral serum labeled with a fluorescent dye (direct method). In indirect method, the unlabelled antiviral serum is applied first, followed by fluorescent labeled antibody to gammaglobulin.
4. Electron microscopy: virus detection in ultra thin section of cell.
5. Detection of enzymes: detection of viral enzymes in culture fluids (eg. Reverse transcriptase of retrovirus).
6. Interference: some viruses (rubella) do not produce CPE but multiply within the host cell.
7. Neutralization test: To detect virus, known specific anti-serum is used which neutralizes virus activity and fails to produce CPE. This is used for CPE producing viruses.