True about plasmodium falciparum is: September 2005

Ans. C: Crescentic macrogametocyte Plasmodium falciparum preferentially infects young erythrocytes, but can infect all stages. Schizonts are small, compact and seldom seen in peripheral smear. Macrogametocytes are crescentic with deep blue cytoplasm and compact nucleus. In falciparum malaria, parasitized erythrocytes may be sequestered in tissue capillaries resulting in a falsely low parasite count in the peripheral blood ('visible' parasitemia). In such instances, the developmental stages of the parasite seen on blood smear may help to assess disease severity better than parasite count alone. The presence of more mature parasite forms (>20% of parasites as late trophozoites and schizonts) and of more than 5% of neutrophils containing malarial pigment indicates more advanced disease and a worse prognosis. One negative blood smear makes the diagnosis of malaria very unlikely (especially the severe form); however, smears should be repeated every 6-12 hours for 48 hours if malaria is still suspected