The role of genetic sequencing and analysis in the polio eradication programme

Figures

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  Figure 1.. Simplified structure of the poliovirus genome adapted from Semler (2004). This diagram highlights the position of the VP1 region of the genome, routinely sequenced for typing purposes, and shows the relative positions of the other major regions mentioned in the text. Red bars show major recombinant regions determined by Stern et al. and arrows the positions of the three gatekeeper mutations for reversion to virulence in serotype two vaccine-derived polioviruses (Stern et al. 2017).

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  Figure 2.. Movement of poliovirus in the west of Tajikistan during the 2010 WPV1 outbreak inferred from a discrete trait analysis of 115 publicly available sequences (Yakovenko et al. 2014). (A) Inferred phylogenetic tree for the poliovirus sequenced in the three regions in 2010. The x-axis is given in decimal years inferred from the clock rate and sampling date of the sequences at the tips of the phylogeny. The inset map shows the location of the four regions in western Tajikistan. (B) Inferred movement events and number of sequenced poliovirus stool samples per region. The breadth of the arrows indicates the number of inferred movement events. The end points of the arrows represent the centroid of each region and not the exact location of reported events. The inset map shows the location of the study area in the wider context of Central and South Asia. (C) Sampling density of sequences over time in the regions shown in (A). Sughd has only one sequence collected on 10 May 2010 so does not feature in this density plot.

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  Figure 3.. Countries reporting circulating vaccine-derived poliovirus (cVDPV) between 1 January 2017 and 1 January 2020. These countries are shaded according to the number of paralysis cases reported over this time period. The red, blue, and green represent serotype one, two, and three VDPVs, respectively. Data from the polio information system of the global polio eradication initiative (World Health Organization 2014c). *Somalia has reported both serotype 2 cVDPV (eight cases) and serotype three (six cases) in the time period covered by this plot.