Armstrong – Table of Contents

endemic form in non-primate hosts such as rodents. The diagnostic criteria that the
Committee recommended for identifying and defining a poliomyelitis strain included: 1)
The clinical and histopathologic manifestation produced in monkeys. If the unknown
viral agent did not produce experimental infection with clinical signs and the
characteristic changes in specific parts of the brain and spinal cord, then the agent was
not a poliovirus. 2) The host range. Primates are the only known experimental hosts for
most strains isolated directly from human or extra-human sources. Since 1939, other than
the Lansing strain, others, such as those designated MEF, Y-SK or Ph isolated from
human hosts had the capacity of producing paralytic poliomyelitis in mice, hamster and
cotton rats, but not in rabbits or guinea pigs. These strains, however, were found to be
related immunologically to the Lansing strain. 3) Immunologic diagnosis. Any virus
which was immunologically distinct from any previously established virus but which
possessed the above-mentioned diagnostic properties, had nevertheless, to be considered
as a poliovirus. Any virus that was immunologically identical to a previously established
poliomyelitis strain had to be tentatively considered as a poliomyelitis virus. 4) Physico-
chemical properties. These properties taken into consideration included small particle
size (8-12mμ), appearance under the electron microscope, and resistance to the lethal
effects of ether.
These criteria helped to differentiate the mouse viruses, often mislabeled “mouse
poliomyelitis,” from the strains responsible for human and animal primate poliomyelitis.
Dr. Max Theiler of the Rockefeller Institute, who adapted the yellow fever virus to mice,
thus enabling the production of a non-virulent vaccine for humans, discovered these
mouse viruses (strains variously designated TO, FA, GD VII). Theiler suggested using