(i)Plasmodium vivax is a digenic parasite , involving two hosts , man as the secondary host and female Anopheles mosquito as the primary host. The life cycle of Plasmodium involves three phases namely schizogony , gamogony and sporogony.
(ii)The parasite first enters the human blood stream through the bite of an infected female Anopheles mosquito . As it feeds , the mosquito injects the saliva containing the sporozoites.
(iii)The sporozoites within the blood stream enter the hepatic cells of the liver and undergoes multiple asexual fission (schizogony) . This produces merozoites which are released from liver cells .
(iv)The merozoites penetrate the RBC's . Inside the RBC of blood , the merozoite of Plasmodium to develop as unicellular trophozoites . The trophozoite grows in size and a central vacuole develops pushing them to one side of cytoplasm and becomes the signet ring stage .
(v)The trophozoite nucleus then divides asexually to produce the schizont. The schizont divides and produces mononucleated merozoites.
(vi)Eventually the erythrocyte lyses , releasing the merozoites and haemozoin toxin into the blood stream to infect other erythrocytes. Lysis of red blood cells results in cycles of fever and other symptoms. This erythrocytic stage is cyclic and repeats itself approximately every 48 to 72 hours or longer depending on the species of Plasmodium involved . The sudden release of merozoites triggers an attack on the RBCs.
(vii)Occasionlly, merozoites differentiate into macrogametocytes and microgametocytes . When these are ingested by a mosquito, they develop into male and female gametes respectively.
