STUDIES ON VARIANTS OF POLIOMYELITIS VIRUS

Abstract

Attempts were made to "convert" highly virulent strains of the 3 immunologic types of poliomyelitis virus (Mahoney, Y-SK, and Leon) into avirulent variants. Tests involving intracerebral, intramuscular, or oral administration of virus to cynomolgus monkeys indicated that mere propagation in cultures of kidney tissue of cynomolgus monkeys had no effect on virulence when single or small numbers of virus particles were used as seed, and harvests were delayed for 24 hours or more after the appearance of cytopathogenic change. On the other hand, passages at 24 hour intervals with large inocula (10⁵ to 10⁶ TCD₆₀) produced culture fluids with diminished virulence and unusual patterns of response in cynomolgus monkeys. Purification of such culture fluids by the terminal dilution technique yielded modified strains which proved to be avirulent after administration by the intracerebral, intramuscular, or oral routes in cynomolgus monkeys.