Plasmodium falciparum, a cause of malaria worldwide, gets into the circulatory system through mosquito bites. P. falciparum tends to invade all ages of red blood cells (RBCs), and the proportion of infected cells may exceed 50%. Schizogony occurs in the internal organs (spleen, liver, bone marrow, etc.) rather than in the circulating blood. Ischemia caused by the plugging of vessels within these organs by masses of parasitized RBCs will produce various symptoms, depending on the organ involved. It has been suggested that a decrease in the ability of the RBCs to change shape when passing through capillaries or the splenic filter may lead to the plugging of the vessels.

Onset of a P. falciparum malaria attack occurs from 8 to 12 days after infection and is preceded by 3 to 4 days of vague symptoms such as aches, pains, headache, fatigue, anorexia, or nausea. The onset is characterized by fever, a more severe headache, and nausea and vomiting, with occasional severe epigastric pain. There may be only a feeling of chilliness at the onset of fever. Periodicity of the cycle will not be established during the early stages, and the presumptive diagnosis may be totally unrelated to a possible malaria infection. If the fever does develop a synchronous cycle, it is usually a cycle of somewhat less than 48 hours.

Severe or fatal complications of P. falciparum malaria can occur at any time during the infection and are related to the plugging of vessels in the internal organs, the symptoms depending on the organ(s) involved. The severity of the complications in a malaria infection may not correlate with the parasitemia seen in the peripheral blood, particularly in P. falciparum infections.

Figure 1. Giemsa-stained Plasmodium falciparum ring forms; note rings with double dots, multiple rings per cell.

Figure 2. Giemsa-stained Plasmodium falciparum gametocyte; RBC outline is just visible.

Additional resources:

1. Garcia, L. S. 2001. Diagnostic medical parasitology, 4th ed. ASM Press, Washington, D.C. (ASM Press website)
2. Garcia, L. S. 1999. Practical guide to diagnostic parasitology. ASM Press, Washington, D.C. (ASM Press website)
3. http://www.med-chem.com/ - PARA-SITE Online