Question
Virus cultivation by cell culture method.
Answer
Virus cultivation by cell culture method: cell cultures are one of three classical methods for propagating viruses in the laboratory (alongside embryonated eggs and laboratory animal inoculation), and are the modern mainstay for diagnostic virus isolation, vaccine production, and research.
Types of cell culture used: primary cell culture (freshly derived from tissue, e.g., primary monkey kidney; limited passage capability, normal diploid karyotype); diploid cell strain (e.g., WI-38, MRC-5 human fibroblast lines — extended but still finite passage, diploid karyotype, used for certain vaccines); continuous (established) cell line (e.g., HeLa, Vero cells — derived from malignant/transformed cells, indefinite passage capability, aneuploid karyotype, widely used for virus isolation and vaccine production).
Procedure: the clinical specimen (suitably treated to reduce bacterial/fungal contamination, e.g., with antibiotics) is inoculated onto a susceptible cell monolayer in appropriate nutrient medium, then incubated at 37°C and observed over days for evidence of viral replication.
Detection of viral growth:
- Cytopathic effect (CPE) — visible morphological changes (rounding, syncytium formation, inclusion bodies, cell lysis) examined by light microscopy, the primary evidence of successful viral growth.
- Haemadsorption — for viruses (e.g., influenza, parainfluenza) causing minimal visible CPE but expressing haemagglutinin on the infected cell surface, detected by the adherence of added red blood cells to the infected monolayer.
- Interference — detecting a non-cytopathic virus by its ability to block/interfere with the CPE of a subsequently added, known cytopathic virus.
- Direct antigen/nucleic acid detection — immunofluorescence or PCR performed on the inoculated culture.
Applications: virus isolation/diagnosis (though increasingly supplemented or replaced by faster molecular PCR-based methods in routine diagnostic practice), vaccine production, antiviral susceptibility testing.