Interval Between Inoculations as a Factor in Interference between Neurotropic Viruses

Abstract

St. Louis encephalitis virus, following nasal instillation, did not protect rats from western equine encephalomyelitis virus inoculated 2, 6, 12, and 24 hrs. later by the same route. If the equine encephalomyelitis virus was inoculated 48 hrs. after the St. Louis encephalitis virus, some interference was noted, since these animals survived longer than did controls. A high degree of protection against equine encephalomyelitis virus was observed in rats that had had St. Louis encephalitis virus inoculated intranasally 72 and 96 hrs. before the equine encephalomyelitis virus was inoculated by the same route. Rats inoculated intranasally with St. Louis encephalitis virus are resistant to nasally instilled equine encephalomyelitis virus for as long as 10 days after the former virus is inoculated, but by the 21st day this resistance disappears.