Pathology of Experimental Vaccinal and Rabies Encephalitis.

Abstract

One of the primary infections 1 of the central nervous system of man, is termed post-vaccinal because it is most frequently found after vaccination against small pox. Yet the identical pathological changes have been described after vaccination against rabies, 2 complicating measles, small pox, varicella and upper respiratory infections. This, of course, does not necessarily mean that a single virus is the responsible agent. The reaction of the nervous system is more or less stereotyped and the same reaction may occur in several diseases such as is the case in Heine-Medin's disease, epidemic encephalitis, and true rabies.

In the human, postvaccinal type of encephalomyelitis there occur disseminated foci of perivascular demyelinization, especially about the veins, coalescing and extensions of the lesions to destroy the whole nerve fiber and to form true softenings composed of intra and extracellular fat. Very few or frequently no lymphocytes are found in the perivascular spaces, and meningeal exudates occur only secondary to the softenings.

Experiments to discover whether the encephalomyelitis associated with vaccination was due to the vaccine virus have given conflicting results. (McIntosh and Scarff 3 and Aldershoff, 4 Eckstein and Herzberg, 5 McIntosh, 6 Hurst and Fairbrother, 7 Thompson, 8 Pette. 9 ) Many investigators contend that vaccination in the human against small pox or rabies, or the exanthematous diseases does not produce encephalitis by the introduction of a specific virus but by stimulating a latent virus to activity.

It was attempted to determine whether in the experimental animal, vaccinia encephalitis could be produced, and whether it resembled the human type. Furthermore attenuated rabies was introduced into experimental animals to determine its pathological characteristics, to compare it with vaccinia encephalitis and human postvaccinal (rabies) encephalitis. Rabies was used particularly because it could be identified by the presence of negri bodies.