Plasmodium is a micro-organism belongs to the phylum protozoa. It causes a disease in the body of human being, called Malaria. The life cycle of plasmodium is completed in the body of two hosts, hence they are known as Digenic Parasite.
- In Body of Man, it is called Primary Host.
- In Body of Female Anopheles Mosquito, it is called Secondary Host.
When a female Anopheles Mosquito bites a healthy person, it transfers into the blood of man, very small spindle or sickle shaped bodies, called sporozoites. They contain cytoplasm and nucleus. In man, the life cycle of plasmodium consists of four phases.
- Pre-Erythroytic Phase.
- Erythroytic Phase.
- Post Erythroytic Phase.
- Gamogony (Formation of Gametes).
i. Pre-Erythroytic Phase
After some time, these sporozoites are transferred from blood to the liver cells. Each sporozoite enters a liver cell and lives as a parasite. It becomes rounded in shape and now it is called cryptozoite. The cryptozoite uses liver cell as its food material.
Schizogony in Liver Cells
In liver cells, each cryptozoite starts multiplication. It divides by a simple process called Schizogony. By this process, it produces many small bodies called Merozoites. These merozoites become free by rupturing of liver cell. Each merozoite enters a new liver cell and behaves as a crypyozoite; it starts the same process again. In this way two or three times schizogony process is completed in liver cells.
After some time, some of the merozoites or cryptozoites are transferred into the blood stream. Each body enters a Red Blood corpouscle (RBC). In RBC, the cryptozoite or merozoite is known as trophozoite. In RBC the trophozoite shows certain changes which are as follows:
1. Ring Like Stage
In Trophozoite, a vacuole appears and its nucleus transfers to the margin. So, it becomes ring shaped, this stage is called Ring Stage.
2. Amoeboid Stage
After some time, the vacuole disappears the nucleus comes back in the center and from the outer surface of trophozoite finger like pseudopodia are produced it becomes amoeba shaped. This stage is called Amoeboid Stage.
3. Schizont Stage
After some time, pseudopodia of trophozoite disappear and it is converted into a rounded body. Now, it is ready to multiply by schizogony process. It is called Shizont. The Shizont divides into many bodies known as Merozoites. The merozoites become free by rupturing the outer layer. These merozoites enter new RBCs. Each merozoite acts as a trophozoite and repeats the schizogony process once again. In this way two or three time this process is repeated in RBCs of man.
iii. Post Erythroytic Phase
From the RBCs some merozoites are again transferred into the liver cells and start schizonic reproduction. It is called post erythrocytic stage.
iv. Gamogony (Formation of Gametes)
When schizony is completed many times in the blood of man, then instead of forming merozoites another type of bodies are produced, known as gametocytes. Now, it is necessary that these bodies should be transferred into the body of female Anopheles Mosquito. In the body of man, the life cycle of plasmodium is completed.
Stage of Life Cycle of Plasmodium in the Body of Female Anopheles Mosquito (Sexual Cycle in Mosquito)
The sexual cycle of Plasmodium is completed in the Stomach of Female Anopheles Mosquito. This cycle consists of following stages:
- Gametogony (Formation of Gametes)
- Syngamy (Fusion of Gametes)
- Sporogony (Formation of Sporozoites)
(Formation of Male and Female Gametes)
Microgametocytes are smaller in size. Each microgametocyte produces many male gametes from its outer surface. These male gametes are thread like structures, after maturation these are separated from microgametocyte and move towards female gamete to take part in fertilization.
Macro gametocytes are larger in size. Each macro gametocyte develops into a single female gamete, called Oocyte. It has a small part at one side, known as reception cone.
(Fusion of Gametes)
The fusion of two male and female gametes is called Syngamy. At the time of fertilization, many male gametes move towards female gamete but only one male gamete is attached with reception cone. Its nucleus is transferred into female gamete and by the fusion of two nuclei Zygote is formed.
(Development of Zygot and Formation of Sporozoites)
After some time, the zygote starts development. It develops into a worm like structure, called Ookinete. The ookinete then changes into a rounded structure, known as Oocyst. It is also covered by a protective covering.
In the oocyst, many bodies are produced by the process of division. These are called Sporoblasts. Each sporoblast produces many thread like structures from its outer surface, called Sporozoites. These sporozoites become free after some time and then they are stored in the salivary glands.
When this female Anopheles Mosquito bites a healthy person, the sporozoites are transferred into his body and hence malaria can be started once again.