Vaccine derived bi- and multi-recombinant Sabin strains

A retrospective analysis of five Sabin intertypic recombinant strains, isolated from human feacal specimens during the time period 1978-1985 in Greece, was performed by RT-PCR, Restriction Fragment Length Polymorphism (R.F.L.P.) and sequencing. Of the studied strains, three (EPA, EPB, EPC) were found to be bi-recombinant Sabin3/Sabin2/Sabin3 (S3/S2/S3), one strain was characterized as a probable S3/S2- CAV18 or CAV21-S2/S1 multi-recombinant (EDP11) and one was identified as a tripartite one S3/S2/S1 (EDP12). Samples EPA, EPB and EPC presented a common recombination junction in the 2C genomic region. Moreover, strains EPA and EPB shared also the second recombination site in the 3D genomic region, whereas the second recombination of EPC was also determined in 3D but in a different nucleotide position. Strains EDP11 and EDP12 presented both identical recombination motifs and recombination sites. The first was detected in the 2C genomic region and the second in the 3D region. Strain EDP11 presented an interesting feature since a sequence of 120 nucleotides seems to have derived from a member of human enteroviruses species C (CAV18 or CAV21). This finding is of great importance, considering that this strain (EDP11) was isolated from an area and time period, where no Coxsackie A virus or poliovirus epidemics occurred. Our study underlines the role of specific positions and motifs of the poliovirus genomic sequences involved in recombination events and prompts that Coxsackie A viruses belonging to human enterovirus species C (genetically closely related to PV) are considered as the possible counterparts of the recombination.