Armstrong – Table of Contents

The incubation period for St. Louis encephalitis and LCM was different in monkeys and
mice. 3) The clinical illness produced by the two viruses was different in monkeys and
mice. 4) LCM was almost constantly found in the blood and spinal fluid of monkeys
during the febrile phase of LCM infection while encephalitis virus had not been
demonstrated in these fluids during this period. 5) LCM failed to produce detectable
symptoms in mice when introduced into the nose (intranasally) while encephalitis virus
“took” readily by this route. 6) The pathology produced by the two viruses in mice and
monkeys was usually readily distinguishable. 7) Cross neutralization tests between St.
Louis encephalitis and LCM showed them to be immunolgically distinct; LCM, likewise,
was dissimilar to the recent encephalitis strains isolated in Japan. These Japanese strains
were epidemiologically and clinically similar to the St. Louis encephalitis strains but
again quite distinct from them. 8) Armstrong said that the LCM agent did not possess the
characteristics of a herpes virus since it had no effect on rabbits. Furthermore, it did not
correspond with any described virus then known to the microbiology community. For all
of these reasons Armstrong considered LCM to be a hitherto undescribed infectious agent
of which the significance in nature was unknown at that time.
In a brief summary of this virology classic: 1) Armstrong isolated a previously
undescribed neurotropic virus encountered during the experimental transmission of
encephalitis virus from the 1933 St. Louis epidemic from which it was readily
differentiated. 2) He outlined the symptoms of the experimental infection in monkeys and
mice. 3) He demonstrated the virus in the central nervous system, spinal fluid, blood and
urine of monkeys and in the brain and blood of mice during the experimental disease. 4)