Genus Plasmodium. Morphological differences in the erythrocyte schizogony of Plasmodium vivax, Plasmodium malariae, Plasmodium falciparum
Genus Plasmodium Overview
- Plasmodium species are protozoan parasites responsible for causing malaria in humans and other animals.
- These parasites are transmitted through the bite of female mosquitoes from the genus Anopheles.
- There are more than 200 known species of Plasmodium, with at least 11 capable of infecting humans. Of these, five are known to cause malaria, including:
- Plasmodium vivax
- Plasmodium malariae
- Plasmodium falciparum
Life Cycle and Transmission
- The life cycle of Plasmodium involves two hosts:
- A human as the intermediate host, where asexual reproduction occurs.
- A mosquito as the definitive host, where sexual reproduction takes place.
- When a mosquito bites an infected person, it takes up sexual forms (gametocytes) of the parasite with the blood.
- These gametocytes undergo sexual reproduction in the mosquito's gut to form sporozoites.
- When the mosquito bites another human, it injects sporozoites through its saliva.
- In the human body, sporozoites first infect liver cells (hepatocytes) and multiply.
- Thousands of merozoites are released from the liver into the bloodstream, where they invade red blood cells (erythrocytes).
Erythrocyte Stage (Schizogony) in Humans
- Once inside red blood cells, Plasmodium follows a distinct developmental process:
- The parasite first appears as a small ring-shaped trophozoite.
- The trophozoite enlarges and often becomes irregular or ameboid in shape.
- The nucleus divides multiple times, forming a multinucleated schizont.
- Each nucleus becomes surrounded by cytoplasm, creating merozoites.
- The infected red blood cell then ruptures, releasing the merozoites into the bloodstream to invade new red blood cells.
- This cycle of invasion and rupture is responsible for the periodic fevers and chills characteristic of malaria.
- Asexual replication in red blood cells is known as schizogony or merogony, which involves multiple mitotic divisions.
- A different reproductive process called endopolygeny is also associated with Plasmodium, where multiple daughter cells form inside one mother cell.
Other Key Features in the Erythrocytic Cycle
- During infection, some parasites develop into gametocytes, the sexual stage required for transmission to mosquitoes.
- These gametocytes mature in the bone marrow, where they target erythrocyte precursors.
- Immature gametocytes are not flexible and tend to stay in the bone marrow.
- Mature gametocytes become more flexible and are able to circulate in the blood, where they can be taken up by mosquitoes.
Morphological Differences in Erythrocyte Schizogony
Understanding how different Plasmodium species look during the erythrocyte stage helps in diagnosing and distinguishing malaria types. Here are the key features for three major species: