Updated by: Arabinda Naik
3rd multiplication phase of schizogony occurs in the erythrocytes known as erythrocytic schizogony. This cycle starts when the micro metacryptozoites enter erythrocytes. Single metacryptozoites enter single RBC and pass through the trophozoite stage, signet ring stage, amoeboid stage, and schizont stage.
a) Trophozoite stage: When metacryptozoites invade the RBC, it becomes rounded with a large nucleus and grows by ingesting hemoglobin of corpuscles. This stage of the parasite is called the trophozoite stage.
b) Signet ring stage: As the trophozoites grow in a size, a large non-contractile vacuole appears which pushes the nucleus towards the periphery and forms a ring-like structure known as the signet ring stage. The signet ring stage is 1/3 to ½ the size of an erythrocyte. The signet ring trophozoites ingest a large portion of the cytoplasm of RBC forming a food vacuole into which it secretes digestive enzymes. The enzyme brings about the proteolysis of blood haemoglobin, which breaks down the protein component into hematin. Protein is used as food by the trophozoite, while unused hematin is deposited in the form of hemozoin (toxic malarial pigment).
c) Amoeboid stage: The signet ring trophozoites enlarge, and vacuole starts disappearing and develops pseudopodial processes in the cytoplasm and changed into the amoeboid stage. This stage is called the amoeboid stage. Currently, small red eosinophilic granules appear in the cytoplasm of the host corpuscle which are known as Schuffner’s granules.
d) Schizont: The amoeboid trophozoites after feeding becomes rounded grow and become erythrocytic schizont. Asexual multiplication takes place in schizont to from 12 to 24 nuclei which get arranged at the periphery and cytoplasmic masses surrounding them. Each cytoplasmic mass with one nucleus becomes an oval-shaped merozoites. This phase is known as erythrocytic schizogony. The haemozoin granules are gathered at the centre. The arrangement is just like the arrangement of petals in rose flowers. So, this stage is called the rosette stage. With the rupture of the red blood corpuscle, the merozoites are liberated into the plasma in the form of erythrocytic merozoites. The merozoites invade fresh corpuscles to repeat the erythrocytic cycle. One complete erythrocytic cycle takes 48 hours.