Highly divergent type 2 and 3 vaccine-derived polioviruses isolated from sewage in Tallinn, Estonia

Abstract

Highly divergent vaccine-derived polioviruses (VDPVs) have been isolated from sewage in Tallinn, Estonia, since 2002. Sequence analysis of VDPVs of serotypes 2 and 3 showed that they shared common noncapsid region recombination sites, indicating origination from a single trivalent oral polio vaccine dose, estimated to have been given between 1986 and 1998. The sewage isolates closely resemble VDPVs chronically excreted by persons with common variable immunodeficiency, but no chronic excretors have yet been identified in Estonia.

Fig 1

Shared noncapsid region recombination sites among Estonian VDPV2 and VDPV3 sewage isolates. (A) Schematic of the poliovirus genome. The single ORF is indicated by a rectangle flanked by the 5′- and 3′-untranslated regions (UTRs); the small protein VPg, covalently attached to the 5′ end, is represented by a circle. Cleavage sites for processing of the polyprotein are indicated by arrows. Dashed lines symbolize virion surface loops forming neutralizing antigenic (NAg) sites 1, 2, 3, and 4. Mosaic structures of VDPV genomes are symbolized by differential shading. (B to E) Maximum likelihood trees (34) (http://www.geneious.com) summarizing sequence relationships among Estonian VDPV2 and VDPV3 isolates and the parental Sabin OPV strain sequences for genomic intervals approximately corresponding to different recombination blocks. (B) VDPV2 and VDPV3 P1/capsid region sequences (nt 763 to 3395) compared to the homologous Sabin strain sequences. (C) VDPV2 and VDPV3 sequences (nt 3396 to 4941) rooted to the homologous Sabin 3 sequences. (D) VDPV2 and VDPV3 sequences (nt 4942 to 5875) compared to the homologous Sabin strain sequences. (E) VDPV2 and VDPV3 sequences (nt 5876 to 7392) rooted to homologous Sabin 1 sequences. Nucleotide positions are numbered according to Toyoda et al. (35). Bootstrap values were obtained after 1,000 replicates and are shown at nodes of consensus trees.