Emergence of vaccine-derived polioviruses, Democratic Republic of Congo, 2004-2011

Abstract

Polioviruses isolated from 70 acute flaccid paralysis patients from the Democratic Republic of Congo (DRC) during 2004-2011 were characterized and found to be vaccine-derived type 2 polioviruses (VDPV2s). Partial genomic sequencing of the isolates revealed nucleotide sequence divergence of up to 3.5% in the viral protein 1 capsid region of the viral genome relative to the Sabin vaccine strain. Genetic analysis identified at least 7 circulating lineages localized to specific geographic regions. Multiple independent events of VDPV2 emergence occurred throughout DRC during this 7-year period. During 2010-2011, VDPV2 circulation in eastern DRC occurred in an area distinct from that of wild poliovirus circulation, whereas VDPV2 circulation in the southwestern part of DRC (in Kasai Occidental) occurred within the larger region of wild poliovirus circulation.

Keywords: DRC; Democratic Republic of Congo; circulating VDPV; poliovirus; vaccine-derived poliovirus; viruses.

Figure1

Geographic distribution of vaccine-derived polivirus type 2 from patients from the Democratic Republic of Congo (DR Congo). Viruses are represented by circles colored by lineage. Viruses that are not assigned to a lineage are categorized as unclassified.

Figure 2

Yearly incidence of vaccine-derived polivirus type 2, Democratic Republic of Congo, 2004–2011. The total number of cases associated with vaccine-derived polivirus type 2 is graphed for each year according to date of onset of paralysis. Viruses that are not assigned to a lineage are categorized as unclassified. VDVPs, vaccine-derived PVs.

Figure 3

Viral protein phylogenetic relationships among vaccine-derived poliviruses isolated from patients with acute flaccid paralysis, Democratic Republic of Congo, 2004–2011. The tree was rooted to the Sabin type 2 poliovirus sequence. The year of onset of paralysis is indicated at the beginning of each virus name, followed by a 5-digit identifier and the province of the case-patient. The numbers of nucleotide differences from the Sabin 2 prototype viral protein 1 sequence are indicated, followed by the name of the lineage. Bootstrap values >80 are indicated on the tree. Scale bar indicates nucleotide substitutions per site.