Blood schizont

Different antimalarials selectively kill the parasite s different developmental forms. The mechanism of action is known for some of them pyrimethamine and dapsone inhibit dihydrofolate reductase (p. 273), as does chlorguanide (proguanil) via its active metabolite. The sulfonamide sulfadoxine inhibits synthesis of dihydrofolic acid (p. 272). Chlo-roquine and quinine accumulate within the acidic vacuoles of blood schizonts and inhibit polymerization of heme, the latter substance being toxic for the schizonts. 

The intrinsic life cycle begins when a female mosquito takes a blood meal. At this time, sporozoites that have matured in the mosquito s salivary glands are inoculated into the blood stream. These sporozoites migrate to the liver where they infect hepato-cytes and progress from early trophozoites to mature schizonts. This process is referred to as the exoerythrocytic cycle. Schizonts in the liver contain thousands of merozoites that are able to infect... 

Primaquine [PRIM a kwin] is an 8-aminoquinoline that eradicates primary exoerythrocytic forms of R falciparum and R vivax and the secondary exoerythrocytic forms of recurring malarias (R vivax and R ovale). In addition, the sexual (gametocytic) forms of all four plas-modia are destroyed in the blood or are prevented from maturing later in the mosquito. Because of its lack of activity against the erythrocytic schizonts, primaquine is often used in conjunction with a schizonticide. 

Over 100 Plasmodium species contribute to the spread of malaria, but only four of these (P. falciparum, P. vivax, P. ovale, and P. malariae) account for human infection, the deadliest being P. falciparum. The malaria life cycle exists first in a mosquito, and then it passes to a human host. An infected female Anopholes mosquito is the host of the parasite s sporogonic hfe cycle. Mature P. falciparum sporozoites reach the salivary glands of the mosquito, and the parasite is transmitted to a human host when the mosquito feeds. During this blood meal, sporozoites are released into the bloodstream where they penetrate hepatic cells and mature into schizonts. The liver cells rupture after approximately two weeks, discharging merozoites into the bloodstream whereupon they infect red blood cells (RBCs). Every 48 to 78 hours, mature merozoites rupture from... 

Within minutes after being injected into the patient s blood, the sporozoites begin entering hepatocytes. where they become primary. schizonts and then merozoites. At this point, there are no symptoms. Depending on the Plttsniodittm species, the merozoites either rupture the infected hepato-cytes and enter the systemic circulation or infect other liver cells. The latter process is seen with P. vivax. P. malatiae. and P. ovale, but not P. falcipantm. and produces secondary schizonts. 

B) Chloroquine is a blood schizonticide but does not affect secondary tissue schizonts... 

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