Summary and Conclusions The influence of age on the susceptibility of mice to infection with the viruses of pseudorabies, Bwamba fever, herpes simplex, St. Louis encephalitis, West Nile disease, Japanese B encephalitis, and Eastern, Western, and Venezuelan equine encephalomyelitis was investigated. Susceptibility to fatal infection with any of these viruses by the cerebral route was not found to diminish.significantly with increasing age. Mice as young as 3 days of age were refractory to peripheral inoculation of the SP strain of pseudorabies virus; this, however, may have been due to the low virulence shown by this strain on cerebral inoculation. With the exception of the Venezuelan equine encephalomyelitis virus, susceptibility to extraneural inoculation of the other viruses was found to decrease with increasing age of the animal. The age at which resistance first appeared depended on the virus. Susceptibility to extraneural inoculation of the Venezuelan equine virus was not influenced by increasing age of the animal. Mice of all the ages tested (from 3 to 233 days) were about as susceptible to extraneural as to cerebral inoculation of the virus. It is concluded that resistance to peripheral inoculation of a virus is not wholly a function of age but is dependent to a variable extent upon the pathogenetic properties of the virus.

Lennette, E. H., & Koprowski, H. (1944). Influence of Age on the Susceptibility of Mice to Infection with Certain Neurotropic Viruses. The Journal of Immunology, 49(3), 175–191.