Malaria
Malaria is one of the most widespread parasitic diseases in the world. It mainly occurs in tropical and subtropical areas but cases are found all over the world due to traveling to and from these areas. A protozoan belonging to the class Sporozoa and the genus plasmodium causes it. Four species are involved--namely, P.vivax, P.ovale, P.malariae, and P.falciparum.
All species differ in morphology, life cycle and the type of disease they cause. The parasite invades and destroys red blood cells. It is transmitted from one person to another through bites of a mosquito of the genus anopheles.

LIFE CYCLE
The life cycle of a malarial parasite involves two hosts and consists of a sexual cycle or sporogony in the mosquito and an asexual cycle or schizogony in humans. Man is actually the intermediate host while the mosquito is the definitive host.

A SEXUAL CYCLE IN HUMANS (SCHIZOGONY)



Malaria growth, penetration and damage of human health, a viral disease mosquito

During a blood meal, a malaria-infected female Anopheles mosquito innoculates sporozoites into the human host. Sporozoites infect liver cells and mature into schizonts, which rupture and release merozoites. This is the pre-erythrocytic schizogony or tissue phase that can persist in the liver and cause relapses by invading the bloodstream weeks or even years later; also called an exoerythrocytic stage). After this initial replication in the liver (A), the parasites undergo asexual multiplication in the erythrocytes (erythrocytic schizogony (B)). Merozoites infect red blood cells. The ring stage trophozoites mature into schizonts which rupture, releasing merozoites.
When the infection is well established, some merozoites differentiate into sexual erythrocytic stages (gametocytes) after about 12 days. Blood-stage parasites are responsible for the clinical manifestations of the disease. The length of erythrocytic cycles and the number of asexual generations vary depending upon the species. If large numbers of red cells rupture simultaneously, a malarial paroxysm results from the toxic material released into the bloodstream. The time taken to complete this cycle varies in different species. In P.vivax it is 45 hours, in P.ovale 48 hours, in P.malariae 72 hours and in P.falciparum 48 hours. Fever occurs at the time of the liberation of the merozoites.

The sexual forms of the parasite


The sexual forms of the parasite the gametocytes, male (microgametocytes) and female (macrogametocytes), are ingested by an Anopheles mosquito during a blood meal. The parasites multiplication in the mosquito is known as the sporogony (C). While in the mosquito's stomach, the microgametes penetrate the macrogametes, generating zygotes.
The zygotes, in turn, become motile and elongated (ookinetes) (10) and invade the midgut wall of the mosquito where they develop into oocysts. The oocysts grow, rupture, and release sporozoites, which make their way to the mosquito's salivary glands. Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle. All sexual and asexual forms of the parasite described in the life cycle are seen in peripheral blood except in P. falciparum where most of the maturation occurs in RBCs sequestered in small vessels.
In this case, only ring forms and gametocytes are seen in the blood. It is important to identify and report P.falciparum because it not only gives rise to immediate serious complications but may also be resistant to ordinary drugs. The incubation period varies from 8-11 days in P.falciparum to 18-40 days in P. malariae. However, sometimes it may be prolonged for months to years.