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

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.

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.

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.

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.