Study of the Malaria Parasite

Phylum: Protozoa
Class: Sporozoa
Genus: Plasmodium

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.

In Man
When the female Anopheles mosquito bites a man and infects the plasmodium into his blood, this infection stage of plasmodium is called sporozoire.

Exoerythrocytic Cycle
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 circular.

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.

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.

Sporogony
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 repeats.