Histologic examination
General histopathology
Histologic examination of biopsy or autopsy tissues is occasionally useful in diagnosing unsuspected cases of rabies that have not been tested by routine methods. When brain tissue from rabies virus-infected animals are stained with a histologic stain, such as hematoxylin and eosin, evidence of encephalomyelitis may be recognized by a trained microscopist. This method is nonspecific and not considered diagnostic for rabies.
Before current diagnostic methods were available, rabies diagnosis was made using this method and the clinical case history. In fact, most of the significant histopathologic features (changes in tissue caused by disease) of rabies infection were described in the last quarter of the 19th century. After Louis Pasteur's successful experiments with rabies vaccination, scientists were motivated to identify the pathologic lesions of rabies virus.
Histopathologic evidence of rabies encephalomyelitis (inflammation) in brain tissue and meninges includes the following:
Mononuclear infiltration
Perivascular cuffing of lymphocytes or polymorphonuclear cells
Lymphocytic foci
Babes nodules consisting of glial cells
Negri bodies