Site analysis of recombinant and mutant poliovirus isolates of Sabin origin from patients and from vaccinees.

Recombination in vaccine strains of polioviruses is a very frequent phenomenon. In the present report, 12 strains isolated from patients after OPV administration and healthy vaccinees were investigated for the identification of recombinant strains as well as for the further analysis of their recombination types and the localization of the recombination sites. The identification of these strains was achieved through reverse transcription, polymerase chain reaction and restriction fragment length polymorphism assays applied to four sequences of the viral genome, which are located in 5'UTR, VP3-VP1, 2C and 3C-D regions. The exact recombination sites were determined by sequencing. Four of the 12 included strains were recombinant in one or more regions. Two of the recombinant strains had an S2/S1 recombination, localized in 3C-D region, one had an S3/S2 localized in 2C and finally a birecombinant strain was identified having an S3/S2/S1 recombination type, with the two recombinations localized in 2C and 3D regions, respectively. The significance of the recombination types and sites observed concerning the viral viability are discussed.