The median parasitaemia in experimental birds was zero before infection, peaked to 0.030% (range: 0.004–0.548%) during the acute phase and dropped to 0.007% during the chronic phase (range: 0–0.038%) (figure 1a). Parasitaemia in the control group remained zero throughout. Figure 1.Parasitaemia in experimentally treated and naturally infected great reed warblers. (a) Frequency of parasitaemia of the lineage pGRW04 induced in the experimental birds during the acute phase of infection (n = 16) and (b) total frequency of parasitaemia in chronically infected wild birds (n = 61). (c) Genus-specific parasitaemia (medians ± 25/75% and the ranges) in wild birds for Plasmodium ssp. (red, n = 18) and Haemoproteus ssp. (dark grey, n = 40).