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Examples of two different patterns of selection during chronic infection. The results of PCR sequencing assays for serum samples obtained at various times postinfection are shown for two ducklings. In the upper panels (bird 40), the wild type (WT)-specific band is seen to increase continuously during chronic infection, while in the lower set of panels (bird 14) the initial enrichment of wild type is followed by replacement with the 2619A-specific band.
