Armstrong – Table of Contents

Leake, Williams and Mayne volunteered to allow the mosquitoes to feed on them despite
the possibility of a serious or fatal outcome. However, and fortunately, nothing happened
so the 1933 investigators could not at that time prove that mosquitoes were the vectors
for transmitting St. Louis encephalitis.
After cessation of the epidemic in St. Louis, Armstrong returned to the laboratory
in Washington, DC, where he continued additional investigative studies of the virus in
monkeys but gradually shifted primarily to white mice. The study in monkey nervous
tissue provided an unexpected surprise to be described. He probed more deeply into the
pathologic changes brought about by the virus in mice under conditions of partial
immunity and seasonal variation (18, 19).
The passage of 70 years has been witness to the major accumulation of
knowledge about the nature of St. Louis encephalitis and its status among the group of
viruses of which it is a member (20). It has been classified as a Flavivirus. Other viruses
in this group producing virulent disease are Yellow Fever, Dengue, Dengue Hemorrhagic
Fever, Japanese Encephalitis and Tick-Borne Encephalitis. There are approximately 60
arthropod-borne or transmitted diseases, including Flaviviruses, of which 30 are known
to cause human disease. The Flaviviruses are spherical, 40-60 nm in diameter and consist
of a lipid envelope covered densely with surface projections comprising 180 copies of the
M (membrane) and 180 copies of the E (envelope) glycoproteins. The viruses are
unstable in the environment and are sensitive to heat, ultraviolet irradiation, disinfectants
(alcohol, iodine) and acid pH. The molecular RNA structure of the viruses has been
described.