Lifecycle of the malaria parasite

Lifecycle of the malaria parasite

     

What are the lifecycle stages of the malaria parasite in the Anopheles mosquito?

  • Lifecycle stages in the mosquito begin when an insect feeds on the blood of a person infected with malaria, in whom the parasites exist as mature male and female pre-reproductive cells called gametocytes. These gametocytes are taken into the mosquito gut when it feeds, where they develop further into male and female gametes.
  • A male gamete fertilizes the female one to form a zygote. The zygote then enlarges to form an ookinete that migrates to the outer wall of the mosquito gut, where parasites named oocysts at this stage multiply several times. Eventually, the new parasites are released and migrate to the mosquito’s salivary glands, ready for transmission to another human.
  • When the mosquito bites another human, the parasites, now called sporozoites leave the mosquito salivary gland and enter the human skin making their way, ultimately, to the human liver.

 

Malaria lifecycle – mosquito stages

What are the lifecycle stages of the malaria parasite in humans?

  • At the same time as she takes a blood meal to nourish her eggs, the female Anopheles mosquito injects sporozoites into the skin of malaria’s next victim, which are rapidly taken up by the liver cells.
  • In all species of Plasmodium, these parasites develop in the liver to form schizonts (the multinucleate stage of the cell during asexual reproduction), from which thousands of merozoites develop.
  • In Plasmodium vivax and Plasmodium ovale only, a proportion of the liver-stage parasites (known as hypnozoites) remain dormant in the hepatocytes. In this stage the parasite can remain dormant for months or several years. These two species of parasite can therefore initiate a cycle of asexual reproduction causing clinical symptoms in the absence of a new mosquito bite, giving P. vivax infection the name relapsing malaria.
  • When the liver cells rupture, the merozoites are released into the bloodstream where they rapidly invade the red blood cells. These blood-stage parasites replicate asexually – rapidly attaining a high parasite burden and destroying each red blood cell they infect, leading to the clinical symptoms of malaria.
  • The trigger is yet unknown, but a small percentage (1%) of merozoites, differentiate into male and female gametocytes, which are taken up by the mosquito during the blood meal. These gametocytes cause the cycle of transmission to continue back to the mosquito.
  • Male and female gametes fuse within the mosquito forming diploid zygotes, which in turn become ookinetes.
  • These ookinetes migrate to the midgut of the insect, pass through the gut wall and form the oocysts.
  • Endomitotic division of the oocysts occur and sporozoites are formed, which then migrate to the salivary glands of the female Anopheles mosquito ready to continue the cycle of transmission back to humans.

Malaria lifecycle – human stages