A naturally occurring highly attenuated strain of type 1 poliomyelitis virus

Summary Twenty strains of poliomyelitis virus recovered from cases of abortive, non-paralytic, poliomyelitis have been tested for neurotropism. Only one strain possessed a low intraspinal activity inCynomolgus monkeys. Six single particle cultures were derived from this naturally occurring highly attenuated strain of type 1 poliomyelitis virus. It has been shown that the original virus consisted of a mixture of virus particles with varying degree of neurotropism. The antigenic and immunizing capacity of one highly attenuated plaque progeny has been tested in guinea pigs and monkeys. Aided with a grant from the National Health Research Council T.N.O.