Morphology and life cycle of malarial parasite -human phase

It is about how the malarial parasite(Plasmodium) multiplies in a human host.

1. MALARIAL PARASITE : MORPHOLOGY AND LIFE CYCLE – HUMAN PHASE

2. The Parasite which cause malaria in man and otheranimals belong to Class:- Sporozoa Suborder – Hemosporidia Genus: Plasmodium Most common species found in man ate: 1. Plasmodium Vivax 2. Plasmodium Falciparum 3. Plasmodium Malariae 4. Plasmodium ovale

3. In the life cycle of Plasmodium, a female Anopheles mosquito (the definitive host )transmits a motile infective form (called the sporozoite) to a vertebrate host such as a human ( the secondary host ), thus acting as a transmission vector.

4. Sporozoites from the saliva of a biting female mosquito are transmitted to either the blood or the lymphatic system of the recipient. Malaria also spreads through: •Transfusion of malaria from the contaminated transfused blood. •By sharing contaminated needle and syringes mostly in the drug abusers. •Congenital malaria which is rare.

5. Asexual cycle or Schizogony  in man It occus in human liver cell (liver schizogony) and in RBC (erythrocytic schizogony). Asexual cycle or schizogony in human is completed in following phases 1. Pre-erythrocytic schizogony 2. Exo-erythrocytic cycle 3. Erythrocytic cycle 4. Post-erythrocytic cycle 5. Formation of gametocytes

6. Pre-erythrocytic cycle Sporozoites enters into parenchymatous cell of liver. Sporozoites in liver cell grow in size and become spherical in shape called schizonts.  The nucleus of schizont multiply asexually (multiple fission) and forms thousands of merozoites. These gives pressure to the wall of liver cell and merozoites are liberated out. The process of formation of many mero zoites from single sporozoites in liver cell is called pre-erythrocytic schizogony. 

7. Erythrocytic cycle Single merozoite enters into single RBC and passes through trophozoite stage, schizont stage and merozoite stage

8. Early Trophozoite This is a ring-like malarial parasite following the invasion of RBCs. Giemsa stain shows it as blue stain cytoplasmic circle connected to red chromatin dot. The space inside the ring is known as vacuole.

9. Trophozoites The shape varies according to the type of malarial parasite.There are a cytoplasmic circle and the chromatin dot. More space is taken by the developing trophozoites. Pigments are brown in color.

10. Immature schizont There is active chromatin replication. Visible cytoplasmic material surrounds the growing chromatin. Pigments are often brown. It occupies more space in the RBC.

11. Mature Schizonts These are characterized by the presence of merozoites.

12. Post-erythrocytic cycle Sometimes, some merozoites produced after erythrocytic cycle invade the liver cell and undergo another schizogonic development in the liver cell. This is called post-erythrocytic cycle.

13. Formation of gametocytes After some generation of erythrocytic cycle, some of the merozoites invade the new RBC. They grow in size but do not develop into schizonts instead they develop into gametocytes. The microgametocytes are smaller in size, cytoplasm stains light blue and nucleus is large and diffuse. The macrogametocytes are larger, the cytoplasm stains deep blue and the nucleus is small and compact.

14. Exo-erythrocytic schizogony The exo erythroic cy cl e resembles the pre-erythrocytic cycl e. Some sporozoites, on entering into liver c el ls do not undergo asexual multiplication but enter into a resting (dormant) phase . The resting stage of the parasite is krown as hypnozo ite. After some period (usually up to 2 years) hypnozoites reactivate to b ec ome schizont s and release merozoites . These merozoites attack red blood cells and are responsible for relapse of malaria . Exo-erythrocytic schizogony is absent in P.falciparum , therefore, relapses do not occur in malaria caused by P. falciparum.