The Virological Surveillance of the Vaccine-derived Poliovirus Circulation in Zhenfeng County of Guizhou Province
For quickly discovering the circulation of vaccine-derived polioviruses(cVDPVs),the imported wild polioviruses and the other vaccine related polioviruses which could cause clinical poliomyelitis and also for strengthening the surveillance of polio virus under the polio-free status,we adopted the methods of virus isolation,virus identification and nucleotide sequencing to carry out the virological examination and made an analysis on the results of polio virus surveillance of AFP cases and their contacts by collecting stool specimens in 2003～2004 from Zhenfeng county and its surrounding 10 counties of Guizhou Province.The results showed that 66 enterovirus(EV) strains had been isolated out of 278 stool specimens.The virus isolation rate of positive cases was 43.4%(66/152),among which 29 strains were polioviruses(PV),37 were non-polio enteroviruses(NPEV).29 PV strains were identified by the National Poliomyelitis Laboratory,among them,24 strains were OPVlike viruses,and 5 strains were Type ⅠVDPVs,all of the VDPVs were isolated from Zhenfeng county in 2004.The EV isolation rate(43.4%)of Zhenfeng and its surroundings counties was higher than that in the whole province in 2003～2004(22.9%～24.6%).The PV isolation rate in 2004 was almost 3 times higher than that in 2003.The isolation rate of Type I PV(34.5%)was obviously much higher than that in former years(the whole provincial average rate of 2000～2002 was 4.1%).This fact indicated that the Type Ⅰ VDPVs had already circulated in Zhenfeng county in our province but had been interrupted after complementary OPV immunization.The infection rate of PV and NPEV has been increasing obviously in the crowd.So it should not be neglected to notice the clinical poliomyelitis caused by non-VDPVs. We should also strengthen both the analysis for monitoring data of poliovirus and the predicted works of epidemic situation in earlier period under the polio-free status.