[Analysis on genetic characteristic of type I poliovirus in China in 2009].

Objective: To study the molecular characteristics of type 1 poliovirus isolated from the acute flaccid paralysis (AFP)surveillance system in China in 2009, to provide a scientific basis for maintaining polio-free status for China.

Method: Polymerase chain reaction (RT-PCR) method was used to amplify the VP1 code region of all the type I poliovirus, and the VP1 coding region of the isolated stains was sequenced and analyzed, the hot-spots and nuerovirulence determinant were analyzed. The phylogenetic tree was constructed based on VP1 region to analyze the evolutionary relationship between the strains.

Result: The results of VP1 sequencing showed that no wild strains or vaccine-derived poliovirus (VDPVs) were detected. However, five pre-VDPVs were found. And nucleotide sequences of two isolates were in high degree of similarity (100%). Sequence alignment showed that two nucleotides in the VP1 region. nt2747 and nt2749 were two mutation hot spots.

Conclusion: According to the epidemiological and laboratory test results of two high variation strains, the short-term circulation may occur probably, and further research are needed. Meanwhile, the existence of mutation hot spots indicated that strains are easy to reverse into wild-type substitutions, and lead to a series changes of neurological and other virulence when the strains are under selective pressure.