The periodic alternation of haploid and diploid states in the life cycle of an organism is called a cycle. The genealogy of the malaria parasite is discussed.
1. Haploid status
(i) Sporozoites: When an Anopheles mosquito biting a healthy human, the sporozoites enter the human body through the saliva of the mosquito. Sporozoites are mobile, slightly curved and both ends of the body are straight. The sporozoites penetrate human liver cells and grow within 30-45 minutes.
(ii) Metacryptomerozotes: Metacryptomerozotes are formed successively from sporozoites. Metacryptomerozites are of two types. Micrometacryptomerozites and macrometacryptomerozites. Micrometacryptomerozites are small in size and have large nuclei. Macrometacryptomerozotes are large in size and have small nuclei. Macrometacryptomerozites invade new liver cells. Micrometacryptomerozites enter the bloodstream and invade red blood cells.
(iii) Merozoite: 12-18 small cells are seen in the cytoplasm of the germ. A nucleus enters each segment. They are arranged in two layers like petals. This condition is called rosette. Each part, including the nucleus, becomes a merozoite.
(iv) Gametocytes: Some merozoites develop into gametocytes. Gametocytes are of two types. Microgametocyte and Macrogametocyte. Microgametocytes are small in size and have large nuclei. Macrogametocytes are large in size and have small nuclei.
(v) Gametes: In the process of exflagellation, the nucleus of each microgametocyte divides into 4-8 pungametes or microgametes. Each macrogametocyte gives rise to one strigamete or macrogamete.
2. diploid state
(i) Zygote: The microgamete enters the macrogametocyte through the fertilization cone. Later their nuclei fuse to form a zygote.
(ii) Uokinete: After 12-14 hours the quiescent spherical zygote becomes elongated and motile. It is called wokkinet or vermicule. Uokinetes are 18-28 microns in length and 3-5 microns in width.
(iii) Oocyst: Within 24 hours the oocinets break through the wall of the mosquito crop and come out and become spherical. It is then covered with a thin film. It is called a oocyst. The oocyst later transforms into a sporozoite.