Virulence and densities of <i>P. c. adami</i> parasites that had undergone 30 passages in naïve mice (derived) with their progenitors (ancestral) (“evaluation experiment 1”).

<p>Curves (panels A and C) represent the kinetics in up to four mice (mean ± 1 s.e.m.) that were sham-vaccinated (no symbols) or AMA-1 vaccinated (filled circles) and infected with derived (red) or ancestral parasites (blue). Interaction plots (panels B and D) show minimum parasite densities and red cell densities in sham- or AMA-1-vaccinated mice infected with ancestral parasites (blue lines) or derived parasites (red lines). Derived parasites induced more anaemia and achieved higher parasite densities than ancestral parasites during infection of naïve mice (A–D; anemia <i>F</i>_1,6 = 6.5, <i>p</i> = 0.04, parasites <i>F</i>_1,6 = 22.3, <i>p</i> = 0.003) and AMA-1 vaccination was disproportionately less effective at containing the derived parasites (C–D; total parasite density×vaccination: <i>F</i>_1,12 = 5.4, <i>p</i> = 0.03).