From An Acorn To An Oak Tree Ps. 92:12

The Malaria Transmission Cycle

by: Peters Olushola

Overview

Malaria is one of the world’s deadly disease caused by a protozoan parasite known as Plasmodium which is transmitted by the female genus of the Anopheles’ mosquito. This parasite has a complex, multi-stage lifecycle. This lifecycle occurs within two living beings:

  • The mosquito (vector)
  • Human (host)

The transmission of malaria involves the cyclical infection of human and the female Anopheles’ mosquito. This cycle can start with an infected mosquito and an uninfected human or an infected human and an uninfected mosquito.

Malaria Parasite Development Stages:

The malaria parasites pass through specific stages of development. These are:

  1. The sporozoites/seed stage – This is the infectious form of the parasite injected by the mosquito in the human bloodstream.
  2. The merozoites/piece stage – This is the stage where the parasites invade the erythrocytes (red blood cells).
  3. The trophozoites/nourishment stage – This is the stage where the parasites multiply in the red blood cells.
  4. The gametocytes/maturity stage – At this stage, some of the merozoites differentiate into gametocytes. These gametocytes are male (microgametocytes) and female (macrogametocytes)

Transmission Cycle:

Here is the stepwise malaria transmission cycle:

  • The cycle starts when an infected female Anopheles mosquito (vector) bites a human (host) thus injecting the Plasmodium in the form of sporozoites into the bloodstream.
  • In few minutes, these sporozoites find its way to the liver.
  • These sporozoites begin asexual multiplication in the liver cells. The process takes about 7-10 days, and during this period, no malaria symptom is experienced by the host.
  • After 7-10 days, these sporozoites reproduce and give birth to merozoites which are then released into the blood circulation where they begin to invade the red blood cells.
  • While in the bloodstream, the merozoites invade the erythrocytes (red blood cells). They multiply in the red blood cells asexually until they burst out of the cells and invade more cells.
  • This sexual multiplication and invasion of the red blood cells by these merozoites continues, and this causes fever for the host anytime these merozoites burst out and invade more red blood cells.
  • Some of the merozoites in the infected red blood cells stop multiplying, and Instead of reproducing they develop into a genitive form of the parasite known as gametocytes. These gametocytes then circulate in the bloodstream.
  • At this stage, when a second mosquito bites an infected human, it ingests these gametocytes which are male (microgametocytes) and female (macrogametocytes).
  • While in the stomach of the mosquito the microgametocytes penetrate the microgametocyte (sexual multiplication) and they generate zygotes.
  • These zygotes further develop into moving ookinetes that burrow through the midgut wall of the mosquito and forms oocysts.
  • The oocysts grow, burst and releases sporozoites which migrate to the mosquitoes’ salivary glands.
  • The mosquito then injects these sporozoites into a new human (host) and thus perpetuate the malaria lifecycle.

 In contrast to the human (host) who suffers from the parasite, the mosquito (vector) does not bear any harm from the parasite. It has been discovered that the parasite and the infected mosquito are mutually beneficial to each other. Plasmodium-infected mosquitoes survive better and display a higher rate of blood-feeding than non-infected mosquitoes.

Less common ways of transmission:

Apart from the female Anopheles mosquito which is the primary transmitter of malaria, there are other ways of malaria transmission which rarely occurs but are worthy of note. They are:

  • Through blood transfusion.
  • Through transplantation.
  • Through infected needles.
  • From mother to fetus during pregnancy.

 Bibliography

 Centre for Disease Control and Prevention. (2018, November 14). Retrieved from CDC

 

Integrated Surveillance and Control Program for the West Nile Virus and Malaria in Greece: Malaria. (2016)

 

The life cycle of the malaria parasite. (2019)

 

Malaria Transmission Cycle. (2019). Retrieved from Bansal Global Hospital