Monkey Pathogenicity of Various Strains of Murine Poliomyelitis Virus. I. Experiments with Lansing,MEF,and Yale-SK Group. ∗

Abstract

Conclusion

The data presented above demonstrate that strains of mouse-adapted human poliomyelitis virus may exhibit wide variations in the degree of their pathogenicity for rhesus monkeys. The Lansing virus, for instance, harvested from remote mouse passages, gave no evidence of being pathogenic for rhesus monkeys in repeated tests. The MEF virus, originally rhesus-pathogenic, apparently suffered a progressive loss of its pathogenicity for rhesus monkeys during serially maintained rapid mouse passages. The Y-SK virus, finally, seemed to have undergone but little change in its pathogenic power for rhesus monkeys as the strain was passed rapidly through mice. It is realized that the described phenomena may not always be duplicated in different laboratories since the Lansing virus has frequently been reported by others as being fully rhesus-pathogenic. Yet the authenticity of our strains is attested by the fact that all three murine strains had fully preserved their biological and immunological characteristics. The observed differences in the degree of pathogenicity for rhesus monkeys and in the extent to which murine virus returns to mice from paralyzed monkeys may be due to individual differences among strains or reflect an attainment of different levels of perfection in the adaptive process.