Paper II
Question
Inclusion bodies.
Answer
Inclusion bodies are distinct, microscopically visible structures forming within infected cells during certain viral infections, representing accumulations of viral particles/proteins/nucleic acid or altered host components — their location, staining, and morphology can provide diagnostic clues.
Classification by location:
- Intranuclear — e.g., Cowdry type A bodies in herpes simplex/varicella-zoster infection; owl’s-eye inclusions in cytomegalovirus infection.
- Intracytoplasmic — e.g., Negri bodies in rabies (in neurons, classically hippocampal/Purkinje cells); Guarnieri bodies in vaccinia/variola.
- Both — e.g., measles virus infection.
Clinical/diagnostic significance: histopathological demonstration of a characteristic inclusion body provided rapid presumptive/confirmatory diagnosis historically, particularly Negri bodies for rabies; modern diagnosis relies more on immunofluorescence and PCR, but inclusion body demonstration remains a useful adjunct in some settings.