Diagnosis of rabies by immunofluorescence in trypsin-treated histologic sections

After trypsin digestion of 4% formaldehyde (10% formalin)-fixed, paraffin-embedded brain sections, immunofluorescence identification of rabies antigen was successful in three human rabies cases and in experimentally infected mice. The method allows better interpretation of the anatomic localization of rabies antigen and will be helpful in studies of the pathogenesis of rabies. It will also be diagnostically useful where fresh or fresh-frozen brain tissue is not available, although it should not be considered as a replacement for standard immunofluorescence and mouse inoculation techniques for rabies diagnosis.