Asexual reproduction of malaria parasites in human red blood cells is called erythrocytic zygogy. After the sporozoite stage, it takes 7-8 days for the malaria parasite to manifest itself in human blood. This period is called pre-patent period. Often the sporozoite remains dormant for months or years after entering the liver cells. Such dormant state of sporozoite is called hypnozoite. The stages of erythrocytic schizophrenia are as follows-
1. Trophozoites: The merozoites enter the red blood cells and become swollen, large and spherical after taking food. This stage is called trophozoite. The trophozoite is 2.5-3.0 µm in diameter. It is a temporary condition.
2. Signet ring: A cavity formed inside the trophozoite. Its cytoplasm moves to the periphery and the nucleus is positioned to one side. In this condition, the germ looks like a stone ring. It is called a signet ring.
3. Amoeboid trophozoites: The cavity of the signet ring disappears within 8 hours. The parasite is irregular in shape, amoeba-like, and motile. This stage is called amoeboid trophozoite. Amoeboid trophozoites consume the protein component of hemoglobin as food. Hematin of hemoglobin is converted to toxic hemogene. At this time the red blood cell is enlarged in size and tiny granules are seen in its cytoplasm. These grains are called Schiffner’s dots. Malaria is diagnosed by the presence of softeners granules in blood cells. Schiffner’s dots are named after the inventor Wilhelm Schiffner (1904).
4. Syzoant: The amoeboid trophozoite has a morphozoite and the parasite is spherical or elongated. Its nucleus divides to form 12-24 daughter nuclei. This multinucleated condition is called zygote. After 36-40 hours it takes up all the space in red blood cells. At this time waste material called hemogene accumulates in the cytoplasm of the parasite.
5. Merozoite: After 45 hours, 12-18 tiny cells are seen in the cytoplasm of the zygote. 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. Merozoites invade new red blood cells. During this time, a large amount of chemical substances called pyrogen accumulates in the blood and due to its effect, fever occurs in the body.
6. Gametocytes: Some merozoites develop into gametocytes after their release from the liver cells. Gametocytes are of two types. Microgametocyte and Macrogametocyte.
(i) Microgametocytes: Microgametocytes are small in size. Its diameter is 9-10 µm and the cytoplasm is light blue. At its center is a large pink nucleus. Its nucleus is small, dense and peripheral.
(ii) Macrogametocytes: Macrogametocytes are large in size. Its diameter is 10-12 µm and the cytoplasm is dark blue.
It takes 96 hours to develop mature gametocytes. It takes 48-72 hours to complete this cycle.