QUESTION # 2 Describe the lifecycle of Plasmodium , the parasite that causes mal

Question

QUESTION # 2 Describe the lifecycle of Plasmodium, the parasite that causes malaria.Start with infection. Describe the role of the sporozoites,merozoites, and gamteocytes in the life cycle, and specify whereyou will find each of these forms of the parasite. Specify whichprocesses occur in the human host and which occur in theAnopholes mosquito host. Include information on bothsexual and asexual reproduction of the parasite. Explain howPlasmodium is able to evade the human immune system, andwhat stages of the life cycle are associated with disease symptoms.If you were a research scientist studying malaria, which of thelife stages of Plasmodium, or its mosquito insect vector,would you target for disease control, and why?
QUESTION # 2 Describe the lifecycle of Plasmodium, the parasite that causes malaria.Start with infection. Describe the role of the sporozoites,merozoites, and gamteocytes in the life cycle, and specify whereyou will find each of these forms of the parasite. Specify whichprocesses occur in the human host and which occur in theAnopholes mosquito host. Include information on bothsexual and asexual reproduction of the parasite. Explain howPlasmodium is able to evade the human immune system, andwhat stages of the life cycle are associated with disease symptoms.If you were a research scientist studying malaria, which of thelife stages of Plasmodium, or its mosquito insect vector,would you target for disease control, and why?

Explanation / Answer

The sporozoites discharged from the salivary glands of themosquito develop in the liver cells, first as schizonts whichtransform and discharge merozoites into the bloodstream. The liverstage is also called the exoerythocytic (or pre-erythrocytic) stageof infection. Merozoites infect the red blood cells where theydevelop into trophozoites, schizonts and merozoites which arecapable of reinfecting other erythrocytes. This stage of theinfection is also called the erythrocytic cycle. The destruction ofthe red blood cells and the release of the parasites' wasteproducts produce the episodic chills and fever that characterizethe disease. Some merozoites from the blood transform intogametocytes which, when taken by the mosquito, initiate sexualdevelopment in the midgut, involving ookinetes and oocysts.

For this reason the human population serves as a reservoir for theinfection of mosquitoes and completion of the transmission cycle isassured. Sporozoites then infect the salivary glands of themosquito. In P.vivax infections which are characterized byrelapses, a dormant stage, called the hypnozoite, remains in theliver. From this stage relapsing infections may occurr at a laterstage. P. falciparum infection relapses do not occur. It is,therefore, assumed that the sporozoites of this species developuniformly producing pre-erythocytic schizonts at the same time andthese schizonts, once formed, discharge all the merozoitessimultaneously; do not remain dormant as in P. vivax.

While all four species have a haemolytic component ie. when a newbrood of parasites break out of the red blood cell this is usuallyof little consequence. The exception is falciparum malaria wherethe parasites multiply very rapidly and may occupy 30% or more ofthe red blood cells causing a very significant level of haemolysis.One reason for this is that P.falciparum invades red cells of allages whereas P.vivax and P.ovale prefer younger red cells, whileP.malariae seeks mature red cells

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