Rabies :Diagnosis and Negri bodies

DIAGNOSIS OF RABIES

• Detection of antigens by immunofluorescence. 
• The specimens collected are :

1. Antemortem
2. Corneal smear
3. Skin biopsy from neck or saliva
4. Postmortem
5. Brain biopsy

• A definitive diagnosis Negri bodies in the brain or spinal cord.
• Rabies virus specific antibodies detection in serum and CSF.(devlop late)
• Two methods are used to detect antibodies
• Indirect fluorescent antibody test
• Rapid fluorescent focus inhibition (RFFIT)
• Reverse-transcription polymerase chain detection of rabies virus nucleic acid in the saliva.
• It is done during early CNS infection.
• Virus isolation
• Isolation of virus by intracerebral inoculation in mice can be attempted from the brain, CSF, saliva and urine 
• Chances of isolation are greater in early disease.
• A more rapid and sensitive method is isolation in the tissue culture cell lines (WI-38, BHK 21, CER)

NEGRI BODIES

• Described by Negri in 1903
• Negri bodies are practically pathognomic for rabies
• Composed of fibrillar matrix and virus particles

STRUCTRE

• Sharply outlined, (2-10 µm in diameter)
• Intracytoplasmic
• Deeply eosinophilic inclusions that measures several microns in diameter.
• Seen in hematoxylin and eosin stained sections.
• Consists of a mass of nucleocapsids
• Surrounded by viral particles budding from intracytoplasmic membranes.

SITE OF OCCURENCE

• Occur in Ammon’s horn of neurons of the brain stem(Hippocampus)
• Purkinje cells of the cerebellum
• Can be seen in axons(infection spread from here)
• Found away from the inflammatory, nonspecific lesions

DETECTION

• Antigen demonstrated in infected cell
• Early confirmation
• Detection by immunofluorescence of biopsy sample