Genomic Analysis of Vaccine-Like Poliovirus Isolates from Stool Specimens of Acute Flaccid Paralysis Cases with Residual Paralysis during the Years 1380-1381 in Iran

The live attenuated oral poliovirus vaccine(OPV), used for many years has reduced the poliomyelitis cases throughout the world wide. Most RNA viruses have highly mutable genomes and polioviruses are among the most rapidly evolving of all RNA viruses. Mutations naturally occurs during their replication in human intestine and in rare instances it can be back mutation to become to neorovirulant(vaccine-associated paralytic poliomyelitis). For many years the role of some critical nucleotides in 5 non-coding region in vaccine-associated paralytic poliomyelitis was known however the investigators have focused on the importance of other nucleotides in capsid regions such as VP1.Therefore mutations in this region of polioviruses isolated from acute-flaccid paralysis cases were analyzed. In Iran the WHO eradication program has been done since 1373 and all acute flaccid paralysis have been studied .During the years 13801381 out of all AFP cases, 5 patients were found to have residual paralysis and 5 vaccine-like polioviruses were isolated from these patients Using icroneutralization test and intratypic differentiation tests (ELISA, probe-hybridization and RT-PCR).Three isolates (no:2,10 and 11) were vaccine-like polioviruses type2. The other isolates (no:7 and 9) were vaccine-like polioviruses type3. The VP1 regions of these isolates were sequenced and analyzed. Sequence analysis showed that 3 vaccine-like polioviruses type2(no:2,10,11) had 1and 2 nucleotide substitutions in VP1 region in comparison with reference Sabin strain type2 respectively and in vaccine-like polioviruses type 3(no:7,9) there was only one nucleotide substitution in isolate7 in this region in comparison with reference Sabin strain type 2. Eradication of wild polioviruses is near however it is essential to identify any mutations in all three Sabin strains and improve our knowledge about molecular pathogenesis of these viruses.