The Importance of Pathogen Load

metric of pathogen load is assessment of parasitemia—the percentage of infected red blood cells (iRBCs). However, anemia is a common consequence of malaria, and so the pathogen burden in blood is more accurately quantified by calculation of the absolute parasite density in blood, taking account of the number of red blood cells per mL. Even this refinement can be very misleading with certain species of Plasmodium (notably P. falciparum and the common ‘‘mouse model’’ parasite P. berghei ANKA) because iRBCs can adhere to the endothelium, which lines small blood vessels (sequestration), resulting in their under-representation in circulating blood [15]. Methods have been developed to estimate total parasite load (parasite biomass) in P. falciparum malaria by measuring the plasma concentration of parasite molecules, which are released into the host circulation, and demonstrate that this is a much better predictor of severity