Aim: To date, there is no study from Asian countries describing the pathology and topographic distribution of virulent, "street" rabies viral infection in the canine brain. In the present study, neuroanatomical distribution of rabies viral antigen in the brains of rabid street dogs, by immunohistochemical techniques is documented and the role of apoptosis in pathogenesis of rabies in natural hosts especially canines infected with street virus is studied.
Materials and methods: 10 brains of adult street dogs from urban areas of Bangalore, South Central India, infected with rabies were collected. The diagnosis was confirmed by immunofluorescent study. The pathomorphological features and the neuroanatomic distribution of the viral antigen by immunohistochemistry were studied. The ability of the virus to activate apoptosis in nerve cells if any, was studied by determining the DNA fragmentation and TUNEL technique in infected canine brains.
Results: The viral antigen was mostly localized to the neuronal perikaryon extending along the dendrites, while occasional astrocytes were also labeled. In the brain, the limbic areas, thalamus and the reticular formation of the brain stem, the trigeminal and the vagal nuclei were involved, corresponding to areas of cholinergic innervation. It is proposed that the preferential involvement of these cholinergic zones could explain some of the clinical features of rabies in canines. The extensive involvement of thalamus and immunolocalization of the rabies viral antigen in the axons are the unusual features noted in a dog's brain in contrast to murine experimental studies with "fixed virus". Characteristic DNA fragmentation forming 180-200 bp, leading to laddering was not seen, indicating apoptosis is not involved in the evolution of lesions in rabies in adult dogs infected by street virus.