- Plasmodium is an intracellular blood parasite which causes a malarial fever.
- Charles Laveran discovered this parasite in the RBCs of man.
- Ronald Ross discovered the oocyst in the gut wall of mosquito and established malarial mosquito relationship.
- Grassi described the digenetic life cycle of Plasmodium.
- There are more than 90 species of Plasmodium known to man but only four species cause different types of malaria in man.
- Plasmodium vivax: It causes benign tertian fever which is recurrent in every alternate days.
- Plasmodium malariae: It causes quartan fever which is recurrent after every 72 hours (3 days).
- Plasmodium falciparum: It causes malignant fever and there is no regularity of the fever.
- Plasmodium ovale: It causes benign sub-tertian fever which is seen after every 48 hours (2 days).
Classification of Plasmodium:
Phylum: Apicomplexa
Class: Sporozoasida
Order: Eucoccidiorida
Family: Plasmodiidae
Genus: Plasmodium
Species: falciparum, malariae, ovale, vivax
- These parasites show an alternation of generation in which they change their hosts to complete their life cycle.
- In human host, the parasite lives in the RBCs and the parenchyma cells of liver.
- In mosquitoes, the parasite resides in the salivary glands after their development in the mosquito’s alimentary canal (the stomach wall).
- Plasmodium produces pigments (typical of their infection) in the RBCs (erythrocytes) during their developmental stages and the pigments are visualized by light microscopy.
- Structurally, Plasmodium is dimorphic, i.e. found in two stages; sporozoite and trophozoite
1.Sporozoite:
- It is the asexual stage in the life cycle of the parasite.
- It is the infective stage, with anterior apical cap.
- It is sickle shaped and both the ends tapering or thin.
- Body is covered with thin and resistant cuticle.
- It is uninucleate with centric nucleus.
- The pellicle of the cell consists of longitudinal contractile microtubules which help in gliding locomotion.
2.Trophozoite:
- It is the feeding stage and is amoeboid shaped (irregular shape).
- It is uninucleate with eccentric nucleus.
- The body is covered with plasmalemma.
- The cell consists of food vacuoles having haemozoin (a toxic product formed after the breakdown of hemoglobin).
