Abstract
Factors influencing the rct character of poliovirus were studied in-vitro to elucidate the mechanisms of change in the character of type 1 wild polioviruses isolated at the 1960 epidemic.
The results were following:
1) It was demonstrated that the wild poliovirus strains were usually consisted of viral particles different in the rct character. Additional evidence were obtained suggesting that the proportion in the number of rct/40+ and rct/40- particles included in each strains might determine the character of the strain as a whole.
2) The wild strains of rct/40- did not change the character after 5 passages in MK cell cultures at 37°C. In contrast, most of the virus strains did change the character after serial passages in cell cultures at 40°C. These results are suggesting that the change in the character of wild polioviruses obtained at the epidemic may be due to the selection of rct/40+ particles by sequential passages of the viruses in the body of febrile patients.
3) The stability of the rct character of attenuated polioviruses (Sabin strains) after human passage differed by the virus type. The type 2 virus was much more stable than type 1, while the type 3 virus was markedly unstable.
