Plasmodium spp possesses a life cycle that shows an alternation of generation accompanied by an alternation of the host. Man represents the intermediate host of the malarial parasite, i.e., the asexual life cycle (cycle of schizogony) occurs in man. The gametogony also starts in the RBC of man and is completed in the female anopheles mosquito.
Table of Contents
Pre-erythrocytic Schizogony
- It comprises a single cycle and lasts for six days.
- The mature pre-erythrocytic schizont measures 60 micrometers in length and 30 micrometers in breadth.
- It contains numerous small merozoites about forty thousand in number.
These merozoites are liberated on the 7th day of infection and enter into RBC to start erythrocytic schizogony. It is now known that they do not re-enter the liver cells and pre-erythrocytic schizogony disappears completely without giving rise to the late tissue phase.
Erythrocytic Schizogony
Plasmodium falciparum does not show a special affinity for any particular type of RBC but invades both the reticulocytes and erythrocytes (i.e., young and mature RBCs).
Schizogony occurs inside the capillaries of the internal organs (spleen, liver, and bone marrow); hence, only the ring forms (but not the growing trophozoites and schizonts) are found in the peripheral blood.
The cycle of schizogony is completed in about 36 to 48 hours.
Multiple infections of the RBCs, i.e., more than one Plasmodium falciparum parasite invades a single RBC (Generally 2-6 parasites).
Gametogony
Plasmodium falciparum has characteristic gametocytes of diagnostic significance. It has sickle-shaped or banana-shaped (i.e., crescent) gametocytes.
Gametogony occurs inside the capillaries of bone marrow and spleen.
With the growth of gametocytes, the red blood cell is gradually used up, and only its skin remains in the form of a sheath enclosing the parasite. The size of the mature gametocyte is about one and a half times larger than the red blood cell harboring it.
Exo-erythrocytic Schizogony
Exo-erythrocytic schizogony is completely absent in Plasmodium falciparum. So in falciparum malaria relapses do not occur.
References
- Venugopal, K., Hentzschel, F., Valkiūnas, G. et al. Plasmodium asexual growth and sexual development in the haematopoietic niche of the host. Nat Rev Microbiol 18, 177–189 (2020). https://doi.org/10.1038/s41579-019-0306-2
- Talman, A.M., Domarle, O., McKenzie, F.E. et al. Gametocytogenesis : the puberty of Plasmodium falciparum. Malar J 3, 24 (2004). https://doi.org/10.1186/1475-2875-3-24
