Numerous oxyhemoglobin crystals form in the digestive tract of fleas infected using a PIER-inducing blood source.

<p>Digestive tracts (A-D) and midgut contents (E-J) dissected from <i>X</i>. <i>cheopis</i> 24h after they had fed on infected rat (A, E, I), guinea pig (B, F, J), mouse (C, G) or gerbil (D, H) blood. Partially digested red blood cell stroma and rhomboid to trapezoid-shaped or rhomboid-shaped crystals were abundant following rat or guinea pig blood meals, respectively. Images are representative of 11–29 dissections. (K) Percentage of total and PIER+ <i>X</i>. <i>cheopis</i> digestive tracts containing oxyhemoglobin crystals one day after feeding on infected blood from one of the four rodent sources. The cumulative mean from 2–4 independent experiments are shown; the number of fleas positive/ total number of fleas dissected is indicated below the <i>x</i>-axis. *p < 0.0001 compared to infectious mouse blood group by chi-square test with Bonferonni post-test. (L) Example of a flea with PIER (infected with rat blood); and (M) a higher magnification image of the proventricular-esophageal junction (dashed-yellow boxed area) containing numerous rhomboid oxyhemoglobin crystals. Three oxyhemoglobin crystals are highlighted in yellow. Image contrast, color balance, and tone were modified for image (M) to more easily visualize oxyhemoglobin crystals. Scale bars: black = 100 μm, blue = 50 μm, green = 20 μm, red = 10 μm.