The Poliovirus Serotype Distribution in Serial Stool Samples from a First iVDPVs Case in China and the VP1 Genetic Characterization of Type III iVDPVs
This paper was to analyze the poliovirus serotype distribution in 12 serial stool specimens from a first immunodeficient vaccine-derived poliovirus(iVDPVs) case in China and the VP1 genetic characterization of the type Ⅲ iVDPVs was also studied.In 2005,polioviruses were isolated from 293 of 5231 AFP cases in 31 provincial polio laboratories using cell culture,virus isolation and micro-neutralization.From one AFP case,numbered CHN9230,12 serial stool specimens had been collected within 2-150 days after onset of AFP and 17 polioviruses were isolated,of which 12 were polio type Ⅱ viruses and 5 were poliovirus type Ⅱ and type Ⅲ coinfected.PCR-RFLP intratypic differentiation(ITD) method and ELISA assay were used to identify the 293 polio isolates.The ITD results indicated the 17 poliovirus isolates were drafted.The VP1 sequence analysis suggested that 12 type Ⅱ isolates were mixture of 2 or more type Ⅱ viruses and 5 type Ⅲ were respectively single viruses.VP1 sequencing of type Ⅲ showed there were 22 to 24 nucleotide substitutions among 5 type Ⅲ polioviruses,the identity was 97.33% to 97.56% as compared with type Ⅲ Sabin strain,all the type Ⅲ strains match the vaccine-derived poliovirus(VDPVs) diagnosis criteria(1% but15% nucleotide identity in VP1 capsid region) of Word Health Organization(WHO).The type Ⅲ poliovirus probably had been replicated for two and half years in this AFP patient who had been immunized five times with the last time in Jan.2005.This study firstly reported the iVDPVs case in China and polioviruses both types Ⅱ and Ⅲ VDPVs were isolated from this iVDPVs case.The iVDPVs appearing in China constitutes a serious challenge to the wild-type poliovirus-free status in China.