It is an intracellular parasite found in the blood of men. They cause malaria,
are malarial parasites, and have 2 hosts.
- Man-Primary host
- Female Anopheles-Secondary host.
The life cycle in men is sexual and in mosquitoes is asexual. There is an
alteration of generation of asexual and sexual cycles. Malarial parasites are
transmitted from person to person by the adult female Anopheles mosquito. The
male mosquito does not play any role in the transmission of malaria, because
they do not feed on blood.
Life Cycle of Plasmodium
Includes 3 stages:
- Pre-erythrocytic or exoerythrocytic cycle in humans
- Erythrocytic or schizygotic cycle in RBC
- Sexual or gametogenic in female mosquitoes.
When the female Anopheles mosquito bites a man and infects the plasmodium
into his blood, this infection stage of plasmodium is called sporozoire.
The exoerythrocytic cycle is the life cycle of parasites inside the RBC of the host.
This is an asexual phase, which results in the production of gametocytes. This
cycle starts with the entry of merozoire into the RBC. In the RBC, the parasite
enters, resulting in a resting period. It attains a round shape called a trophozoire.
In the trophozoire, a large vacuole develops and pushes the nucleus to one side.
This stage is known as the signet ring. The vacuole disappears; the parasite fills
the RBC to become a schizont ring.
The schizont mature and undergo fusion to form mesozoites. They are
released into the blood stream by the bursting of RBC. The mesozoites attach
fresh RBC and the cycle repeats. After a few generations, some of the mesozoites
develop into gametocytes in the RBC. There are 2 types of gametocytes. One is
the macrogametocyte, which has a small nucleus, large cytoplasm, and is
Both the gametocytes do not undergo further development until they reach
the stomach of the Anopheles. If they cannot reach it, they disintegrate.
When an Anopheles mosquito bites a malarial parasite patient for blood in
the stomach of the mosquito, only mature gametocytes survive to develop into
gametes. Others disintegrate in the process of gamete formation, called gametogamy.
During gametogamy, the microgamete becomes active. It produces 6–8 slender
nucleated bodies, called male gametes, by a process of exflagellation. The
microgamete settles freshly in the stomach of the mosquito. The macrogametocyte
undergoes the maturation phase and develops into a female.
The male gametes fuses with the female gamete to form a spherical zygote and
remains inactive for some time. Later it transforms into an elongated wormlike
mouth structure called ookinite. Ookinite pierces through the wall of the stomach
and binds to the outer layer of the wall. There it becomes round, secretes a cyst
wall, and grows in size. This stage is called oocyst. The nucleus divides into bits,
each of which develops into slender sickle-shaped cell bodies called sporozoire.
The mature cyst ruptures to liberate the sporozoites into the body cavity of the
mosquito. Formation of sporozoites from zygotes is called sporogony. These
sporozoites are ready to reach the salivary glands, and when a mosquito bites
a healthy person, sporozoites are released to his blood stream, and the cycle