Question
Cytopathic effect (CPE)
Answer
Cytopathic effect (CPE) refers to the visible, microscopically observable morphological changes that occur in cultured host cells as a result of viral infection and replication — the basis of the classical, traditional method of detecting and presumptively identifying viruses grown in cell culture.
Types of CPE (the specific pattern often provides a presumptive clue to the virus family involved):
- Rounding and detachment of cells — a common, non-specific pattern seen with many viruses (e.g., enteroviruses, adenoviruses).
- Syncytium (giant cell/multinucleated cell) formation — adjacent infected cells fuse together to form large multinucleated masses; classically seen with paramyxoviruses (measles virus, respiratory syncytial virus — the latter’s very name derives from this characteristic effect) and herpesviruses.
- Inclusion body formation — intranuclear or intracytoplasmic inclusions (e.g., Cowdry type A bodies with herpes simplex virus).
- Focal degeneration — localized areas of cell destruction spreading outward from an initial focus, seen with herpesviruses.
- Complete cell destruction/lysis — extensive, rapid cell death, seen with poliovirus and other enteroviruses.
- Vacuolation — cytoplasmic vacuole formation, e.g., with SV40 virus.
Clinical/laboratory significance: observation of CPE in an inoculated cell culture (using a susceptible cell line appropriate to the suspected virus) confirms viral growth and, combined with the characteristic pattern and time course of CPE development, provides presumptive identification of the virus family — historically the mainstay of diagnostic virology before molecular methods, and still used in some settings and for viral isolation/characterization, though largely supplemented or replaced by faster PCR-based methods in routine modern diagnostic practice.
Related phenomenon — haemadsorption: some viruses (e.g., influenza, parainfluenza) that produce minimal or no visible CPE can still be detected by their ability to cause red blood cells to adhere to the surface of infected cell monolayers (via viral haemagglutinin expressed on the infected cell surface), an alternative indirect method of confirming viral growth in culture.