A 10-year-old child bitten by a stray dog 2 months ago now develops hydrophobia, aerophobia, hypersalivation and progressive encephalitis. Post-mortem brain examination shows Negri bodies in Purkinje cells of cerebellum and pyramidal cells of hippocampus. What are Negri bodies composed of?
- A Prion aggregates of misfolded PrPSc protein
- B Aggregates of viral nucleocapsid (N protein + RNA) representing cytoplasmic viral inclusion bodies — intracytoplasmic acidophilic inclusions ✓
- C Host mitochondrial fragments displaced by viral replication
- D Perivascular lymphocytic cuffing around neuronal cell bodies
Explanation
Negri bodies are pathognomonic intracytoplasmic acidophilic inclusion bodies of rabies virus infection, found in pyramidal cells of the hippocampus (Ammon's horn) and cerebellar Purkinje cells. They consist of viral RNA-nucleoprotein (N protein) complexes — essentially the accumulated viral matrix. They are eosinophilic, roughly oval/round, 2–10 µm, may contain basophilic granules. Negri bodies are the definitive histopathological diagnosis but sensitivity is ~80%. More sensitive tests: direct fluorescent antibody (DFA) test and RT-PCR on brain tissue. Prion inclusions (PrPSc) are seen in spongiform encephalopathies; perivascular cuffing is a general viral encephalitis finding.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.