Plasmodium of Malaria – An Overview

Plasmodium of Malaria Parasite

There are four species of the genus plasmodium: Plasmodium Vivax,
Plasmodium falciparum, P malaria, and Plasmodium ovale. They are protozoa
causing malaria in man. Infection with the plasmodium causes intermittent fever
which is named as malaria.

1. Life Cycle

The malaria parasite passes there life cycle I’m two hosts in male
indeterminate host and female anopheles mosquito definitive host. Asexual
development of parasites occurs in man and sexual development in the mosquito.
Human Cycle

The sporozoite is the infective form of the malaria parasite. These sporozoites
are present are introduced directly into the blood circulation. In this way, the human cycle starts and it comprises of following stages:
  1. Preerythrocytic Schizogony

  2. Erythrocytic Schizogony

  3. Gametogony

  4. Exoerythrocytic Schizogony

1. Preerythrocytic Schizogony


Before starting erythrocytic schizogony in blood, sporozoites undergo a
development phase inside the liver cells. This phase of development is known as
pre-erythrocytic schizogony. The sporozoite becomes round inside the liver
parenchymal cells. They experience different atomic divisions and form into
schizont.



The size of schizont varies in different species and it contains
20,000 – 50,000 merozoites.
The pre-erythrocytic cycle lasts for 8 days in Plasmodium Vivax, 6
days in Plasmodium falciparum, 12-13 days in Plasmodium malaria, and 9 days in
Plasmodium ovale. After completion of this cycle, the liver cells rupture and
release merozoites into the bloodstream.
2. Erythrocytic Schizogony
The merozoites released from pre-erythrocytic schizogony penetrate
red blood cells. They pass through the stages of trophozoite, schizont, and
merozoite. Depending on the species of the malarial parasite, there may be 6-24
merozoites in red blood cells. The red blood cells rapture to release the
merozoites which attack new red blood cells and continues their erythrocytic
schizogony repeating the cycle.

In Plasmodium falciparum infection,
erythrocytic schizonts aggregate in the capillaries of the brain and other internal
organs, so that only ring forms are found in the peripheral blood.

3. Gametogony

Some merozoites of erythrocytic schizogony develop into male and
female gametocytes know as micro gametocytes and macro gametocytes
respectively. They develop in the red blood cells. These are sexual forms and
are found in the peripheral blood.

The micro gametocytes of all the four
species are smaller in size, cytoplasm stains light blue and the nucleus is
large and diffuse. Interestingly, the full-scale gametocytes are bigger, the
cytoplasm recolors dark blue and the core is little and reduced.
4. Exoerythrocytic Schizogony


The exoerythrocytic cycle resembles the pre-erythrocytic cycle.
Some sporozoites, on entering into liver cells. Try not to experience
abiogenetic duplication yet go into a resting stage. The resting phase of the
parasite is known as hypnozoite.



After some period hypnozoite reactivates to
become schizont and release merozoites. 
These merozoites attack red blood cells
and are responsible for the relapse of malaria.  Exoerythrocytic
schizogony is absent in plasmodium falciparum, therefore, relapses do not occur
in malaria caused by plasmodium falciparum.
Mosquito Cycle
The sexual cycle of the malaria parasite actually starts in the
human host by the formation of gametocytes which are then transferred to
mosquito for further development. A female anopheles during its blood meal form
of the parasite. Only the mature sexual forms are capable of further
development in the mosquito and the rest die immediately.

In the midgut of the
mosquito, one micro gametocyte develops into a 4 to 8 thread-like filamentous
structure named micro gametocytes. Form one macro gametocytes only one
macrogamete is formed. 
Fertilization occurs when a micro gamete penetrates into a micro
gamete is known as a zygote.

The zygote protracts into an ookinete. As oocyst
develops, it increments in size and an enormous number of sporozoites create
inside it, The number of oocysts in the stomach wall varies from a few to
more than a hundred.

The oocyst ruptures and releases sporozoites in the body
cavity of the mosquito. The sporozoites are distributed into various organs and
tissues of the mosquito. However, they have a special predilection for salivary
glands. The mosquito is now capable of transmitting the infection to man.
Disease
Plasmodium causes intermittent fever which is named as malaria.
The incubation period is 10-14 days in Plasmodium vivax, Plasmodium falciparum , and Plasmodium ovale but it is 20-30 days in Plasmodium malariae. The typical
clinical features consist of febrile paroxysm followed by anemia and
splenomegaly.

Plasmodium falciparum is the most pathogenic of the plasmodium
species infecting man. There are no relapses in Plasmodium falciparum infection
but relapses occur in Plasmodium vivax infection. Plasmodium falciparum invades
erythrocytes of all ages but Plasmodium vivax infects only young erythrocytes.

Complications of plasmodium infections include pernicious malaria
and blackwater fever. Pernicious malaria is a life-threatening complication
that sometimes occurs in acute falciparum malaria. Various manifestations of
pernicious malaria are grouped as cerebral malaria, algid malaria, and
septicaemic malaria.

Blackwater fever is a manifestation of infection with
Plasmodium falciparum occurring in those persons who have been previously
infected and have had an inadequate dose of quinine. It is characterized by
intravascular hemolysis, fever, and hemoglobinuria.
Treatment Of Malaria
Chloroquine is used for the treatment of acute malaria.
Mefloquine is active against chloroquine-resistant strains.
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