| Poliomyelitis (polio) is an acute infectious disease and mainly infected children, it can be prevented by inactivated poliovirus vaccine (IPV) or live Oral Poliomyelitis Attenuated Vaccine (OPV). The global Polio Eradication Initiative began in 1988. Wild poliovirus (WPV) type-2 was last reported in October 1999, by 2009, transmission of indigenous type 1 and type 3 (WPV1 and WPV3) had been interrupted in all but 4 countries worldwide. (The countries where transmission has not been interrupted are Afghanistan, India, Nigeria and Pakistan.)Since 1995, the indigenous wild poliovirus has not been isolated in China. In 2000, including China, the World Health Organization (WHO) Western Pacific (WPRO) was certified as "polio-free" status. OPV was used to prevent and contral poliomyelitis in China now. OPV strains can mutate during their replication in the human intestine and some mutations may result in recovery of the capacity for higher neurovirulence and lead to vaccine associated paralytic poliomyelitis (VAPP).These strains were excreted to the environment by the inoculators, and they can affect other non-inoculators, if they can live for a longer time and circulating (the mutation rate of VP1 nucleotide acid is equal to or larger than 1%), it is called vaccine-derived Poliovirus (VDPV). Although China is in polio-free status now, the transmission of wild poliovirus type I has not been interrupted globally, and there is still a risk of importation of wild poliovirus to China. To study the molecular characteristics of type 1 poliovirus and provide a scientific basis for maintaining polio-free status for China, we used Polymerase chain reaction (RT-PCR) method amplify the VP1 code region of all the type I poliovirus isolated from the acute flaccid paralysis (AFP) surveillance system in China in 2009, 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, and sequenced and analyzed the VP1 coding region of the isolated stains. The results of VP1 sequencing showed that no wild strains or vaccine-derived poliovirus (VDPVs) were detected. However, five pre-VDPVs were founded. And nucleotide sequences of two isolates are in a high degree of similarity (100%). Sequence alignment showed that two nucleotides in the VP1 region, nt2747 and nt2749, are two mutation hot spots. According to the epidemiological and laboratory test results of two height variation strains, the probability that the occurrence of a short-term circulation could not be ruled out, and further study are needed to confirm. Meanwhile, the existence of mutation hot spots indicated that when the strains are under selective pressure, they are easy to reverse into wild-type substitutions, leading to a series of neurological and other virulence changes.According to Real-time RT-PCR recommended by WHO and developed by USA Centers for Disease control and prevention,6 respected poliovirus isolates were tested for intratypic differentiation (ITD) and vaccine derived polioviruses (VDPVs) screening. The results of Real-time RT-PCR for 6 isolates were compared with those of VP1 region sequencing. We found that the Real-time RT-PCR cannot identify 5 Pre-VDPVs. The Real-time RT-PCR retrospective and prospective researches for large scale of polioviruses will be needed to determine if the assay is applicable to Chinese Poliomyelitis Laboratory Network. |
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