The action on mice of several neurotropic viruses was studied with reference to factors which influence
infection. With pseudorabies virus, section of the sciatic nerve with inoculation into the ipsilateral foot pad significantly retarded the speed of
infection. The virus ascended other nerves of the leg, but at a slower rate. It would appear that the number of nerve fibers available for passage may play a rôle in the speed with which
infection occurs with this virus. When pseudorabies virus was inoculated into an area of
inflammation its effects were markedly lessened. Similar experiments with unmodified
equine encephalomyelitis virus which, unlike
pseudorabies, does not ascend along local nerves, showed no impedance of
infection.
Brain trauma did not change the rate of
infection with the viruses of
St. Louis encephalitis, herpes, or
pseudorabies. But
intraperitoneal injection of
glycerine, followed by intramuscular inoculation of St. Louis virus, resulted in marked facilitation of
infection, as already remarked of fixed
equine encephalomyelitis virus. This phenomenon did not occur with
pseudorabies or herpes. In contrast to certain other viruses, pseudorabies and herpes viruses were only slightly more effective in young mice than in adults. With St. Louis virus, as with fixed
equine encephalomyelitis viruses, inoculation into the eye or nose was far more effective than other peripheral routes. This was not the case with
pseudorabies. Herpes, however, also showed greater sensitivity of the intraocular route. After injection into the eye, St. Louis and fixed
equine encephalomyelitis viruses invaded the optic pathway, while herpes and
pseudorabies avoided the optic fibers and attacked the trigeminal nerve. These phenomena are discussed in the light of cellufugal and cellupetal progression of viruses. The similarities in the action of fixed
equine encephalomyelitis and St. Louis encephalitis viruses are discussed and contrasted with herpes and
pseudorabies.