Genomic modifications in naturally occurring neurovirulent revertants of Sabin 1 polioviruses.

Five type 1 Sabin-like poliovirus strains were isolated from paralytic cases of poliomyelitis. Their Sabin origin was confirmed by antigenic analysis with monoclonal antibodies and restriction fragment length polymorphism (RFLP) assay. Several nucleotide positions known to play a role in the reversion towards neurovirulence were examined: viz 480, 2741, 6203, 7441. Analysis was performed by enzymatic restriction and partial sequencing of PCR-amplified genomic segments. All the strains bore the reversion G > A at residue 480; in four of the five viruses, only this reversion was found. The fifth strain presented four additional reversions and several new mutations. These results indicate that, during multiplication in the human gut, Sabin 1 poliovirus carrying one or several mutations related to reversion towards neurovirulence can be selected.