Enterovirus C strains circulating in Nigeria and their contribution to the emergence of recombinant circulating vaccine-derived polioviruses.

Between 2005 and 2011, 23 lineages of circulating vaccine-derived polioviruses (cVDPVs) were detected in Nigeria with nonstructural region (NSR) of non-polio enterovirus C (NPEV-C) origin. However, no information exists on NPEV-C strains recombining with oral poliovirus type 2 vaccine strains (OPV2) to make type 2 cVDPVs (cVDPV2s) in Nigeria. This study was therefore designed to investigate the probable contribution of NPEV-Cs recently isolated in the region to the emergence of cVDPV2s. Eleven enterovirus C (EV-C) strains (8 NPEV-Cs and 3 PV2s) previously isolated by the authors were analysed in this study. All 11 isolates were assayed for cell-line-dependent growth restriction in four cell lines (LLC-MK2, MCF-7, RD and L20B). Subsequently, the isolates were subjected to RT-PCR specific for VP1 and 3Dpol/3'-UTR of EV-C. All PCR products were sequenced, and phylogenetic analysis was performed. All eight NPEV-Cs replicated exclusively in the MCF-7 cell line, while the three PV2s replicated in all four cell lines. The eight NPEV-Cs were identified as CVA13 (7 isolates) and CVA20 (1 isolate) by VP1 analysis, while all 11 isolates were confirmed to be EV-Cs by 3Dpol/3'-UTR analysis. In addition, phylogeny violations suggested that some cVDPVs might have recombined with common ancestors of the NPEV-Cs described in this study. This was confirmed by the scatter plot of divergence in VP1 against that of 3Dpol/3'-UTR sequences for pairs of isolates. The results of this study showed that the NSR of unknown origin found in cVDPVs from the region might have come from NPEV-Cs (e.g., CVA13 and CVA20) circulating in Nigeria.