2015م - 1444هـ
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Subphylum Sporozoa - Malaria

A. Introduction

Four species of malaria parasites infect humans, Plasmodium vivax, P. ovale,

P.malariae, and P. falciparum. All are transmitted by female Anopheles sp. mosquitoes.

Recent years have seen a resurgence in numbers of cases of malaria due to increased

travel to malarious regions, political and civil unrest, development of drug resistance by

malaria parasites, resistance to insecticides by mosquitoes, and government’s failure to

adequately fund control measures.

B. Life cycle:

The mosquito injects sporozoites while feeding; these enter hepatocytes within 30

minutes and multiply asexually forming merozoites. Upon rupture of the infected hepatic

cell, merozoites invade red blood cells and begin an erythrocytic cycle - rings to

trophozoites to schizonts or gametocytes. Schizonts continue the erythrocytic cycle,

whereas, gametocytes are picked up by female Anopleles spp. mosquitoes. In the

mosquito, sexual reproduction takes place. Gametes are fertilized; the resulting motile

ookinete penetrates the mosquito’s stomach wall forming a zygote on the hemocele side

of the stomach. Sporozoites develop within the zygote; this structure ruptures and

escaping sporozoites invade the salivary gland of the mosquito