Figure 1.

Falciparum infections during early childhood for 8 twin pairs. In each panel, smear results (parasite counts per 300 white blood cells [WBCs]) for the 2 twins in the pair are represented by blue and red lines. Hemoglobin type and ID numbers are indicated in the upper left corner. Circles represent time points when smears were performed; black squares, clinical episodes. Orange shaded areas represent the transmission season (July–December). To facilitate visualization of low-density infections, infections with <100 parasites per 300 WBCs are represented by stars. Groups defined in the text are shown on the top right corner in each panel. Pairs in group 1 were subcategorized in those with similar parasite levels during infection (group 1a) and those with discordant levels (group 1b), in which the twin with highest parasitemia had ≥1 smear with parasite counts ≥5-fold the maximum count of her or his sibling. Group 2 corresponds to pairs in which only 1 twin had infection. Group 3 includes pairs with discordant hemoglobin S mutation status. Note that here only the 2 pairs in each group with the longest follow-up are presented (the same information is shown for all twin pairs in Supplementary Figure 1). In group 3, only individuals with AA genotype had hyperparasitemia (here defined as > 3750 parasites per 300 WBC; see also Supplementary Figure 3). Clinical episodes in which only nonfalciparum parasites were detected are represented by black squares that are not linked to the plot lines and whose y-axis coordinate is defined by the nonfalciparum parasitemia.