Anemia in parasite- and recombinant protein-immunized aotus monkeys infected with Plasmodium falciparum.

Trevor R JonesMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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David F StroncekMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Alfonso S GozaloMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Nicanor Obaldia 3rdMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Ellen M AndersenMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Carmen LucasMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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David L NarumMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Alan J MagillMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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B K L SimMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Stephen L HoffmanMalaria Program, Naval Medical Research Center, Silver Spring, Maryland 20910, USA.

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Plasmodium falciparum-induced anemia was characterized in Aotus monkeys repeatedly immunized by infection with P. falciparum (FVO strain) parasites, then cross-challenged with CAMP strain, or in monkeys receiving blood stage challenges as part of malaria vaccine trials. In 4 studies, 25 (30.5%) of 82 monkeys had at least a 50% reduction in hematocrit; mean day of maximum parasitemia was 12.5, whereas the mean day of minimum hematocrit was 18.8 (P < 0.0009). Decreased hematocrit levels were not associated with reticulocytosis until parasite densities decreased significantly from peak levels. Direct antibody tests to detect IgG and C3d on the surface of erythrocytes were negative. Nonantibody/noncomplement-mediated lysis of uninfected erythrocytes seems to be the principal cause of the anemia, and it also seems that bone marrow suppression and lysis of infected erythrocytes contributed to the anemia. Partial immunity-whether induced by repeated immunization with whole parasites or with vaccine-seems important to the development of anemia.

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