Negri bodies are discrete, intracytoplasmic, deeply eosinophilic inclusions that measure several microns in diameter. In about 75% of cases of rabies these can be seen on hematoxylin and eosin stained sections. Image Link
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Since first described by Negri in 1903, the presence of the Negri bodies are practically pathognomic for rabies and are an important diagnostic finding. Image Link
They occur in neurons of the brain stem, particularly those in the hippocampus, and in the Purkinje cells of the cerebellum. Image Link
Ultrastructural studies have shown that Negri body consists of a mass of nucleocapsids surrounded by viral particles budding from intracytoplasmic membranes. Image Link
Those bodies can be seen in axons, and it is in this way that virus spreads from the central nervous system to many organs of the body.
Because Negri bodies are usually seen in intact neurons, they are found away from the inflammatory, nonspecific lesions.
Rabies viral antigens can be demonstrated in infected cells by means of fluorescent antibody technique.
Antigens can be shown to be present in cells in the absence of Negri bodies, and hence this technique is much more sensitive than the search of sections of brain for the pathognomonic cytoplasmic inclusions.
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