FMGE 2009 — Pathology

Question 1: Confirmatory diagnosis of rabies on postmortem:

• A. Negri bodies in saliva
• B. Anti-rabies antibodies in blood
• C. Negri bodies in brain (Correct Answer)
• D. Negri bodies in corneal scrapings

Explanation: ***Negri bodies in brain*** - The presence of **Negri bodies** (eosinophilic intracytoplasmic inclusions) found upon histological examination of brain tissue (specifically **Purkinje cells of the cerebellum** and **pyramidal cells of the hippocampus**) is the **pathognomonic microscopic finding** for rabies [1]. - This is considered the **gold standard for postmortem confirmation** because the rabies virus primarily targets and replicates in neuronal tissue, leading to these characteristic inclusions. *Negri bodies in saliva* - While rabies virus can be present in saliva, the presence of **Negri bodies** themselves in saliva is **not a diagnostic criterion**. - **Viral isolation** or **PCR** from saliva might detect the virus, but Negri bodies are cellular inclusions, not free virus particles. *Anti-rabies antibodies in blood* - The presence of **anti-rabies antibodies** in blood typically indicates **prior exposure or vaccination**, not necessarily an active, fatal infection as required for a postmortem diagnosis. - In unvaccinated individuals with clinical rabies, antibodies may only appear in the very late stages, if at all, due to the rapid progression of the disease and the virus's evasion of the immune system in the CNS. *Negri bodies in corneal scrapings* - While rabies virus antigens can sometimes be detected in **corneal impressions or scrapings** during life using **fluorescent antibody tests**, Negri bodies are not typically found or used for diagnosis in these samples [1]. - Corneal testing is primarily a **pre-mortem diagnostic aid** for antigen detection, not for visualizing Negri bodies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1279-1280.