Adaptation of Mahoney, Type I, poliomyelitis virus to suckling mice

Abstract

The Mahoney, Type I, poliomyelitis virus undergoes two ‘cycles’ of multiplication in the CNS of suckling mice—the first within 48 hr. after intracerebral inoculation, and the second approximately 10 days later. The former may not be associated with paralysis whilst the latter usually is. By to-and-fro passage in suckling mouse brain and monkey kidney-tissue culture there is a gradual increase in the amount of virus obtained during the early multiplication cycle in suckling mouse brains and associated with this is the occurrence of early paralysis in 80% or more of these mice. The virus capable of causing early paralysis in infant mice is gradually lost by direct mouse-to-mouse passage. The occurrence of two variants is postulated, one of these apparently nonparalytic and multiplying selectively in suckling brains. The author would like to thank the late Prof. M. van den Ende for his stimulating discussions and advice, Dr P. K. Olitsky of New York for his constant interest, and Mr T. C. Norcott for his able technical assistance.