Plasmodium Life Cycles

Question 1

Describe the life cycle of plasmodium vivax/ falciparum

Answer 1

1. Infected mosquito bites human → injects sporozoites.
2. Spots sporozoites travel to the liver, where they mature into merozoites.
3. Merozoites enter red blood cells, developing into trophozoites, then schizonts, and infect more RBCs.
4. Some merozoites develop into gametocytes in the RBCs.
5. Mosquito bites infected human, ingesting gametocytes.
6. In the mosquito, the gametes form a zygote, which becomes an ookinete and eventually an oocyst in the mosquito’s gut.
7. The oocyst produces sporozoites, which move to the mosquito’s salivary glands, ready to infect a new human host.

Question 2

What is important to note about the liver stage of p. vivax infection?

Answer 2

Hypnozoints can form (dormant) that can lie in wait for up to eight years and cause a relapse.

Question 3

Explain Sequestration / cytoadherence in P. falciparum

Answer 3

During the asexual replication cycle in human RBCs, P. falciparum
undergoes its maturation in the microvasculature, deep within tissue
(rather than moving around the body in the peripheral blood circulation)

• The older stages, late trophozoite and schizont stages, are therefore not seen in the peripheral blood (only rings are seen)
• Older stages of P. falciparum undergo a process called sequestration, in which they adhere through a process called cytoadherence to endothelial cells within the small vessels of the body (located deep within tissue)

Question 4

Explain how the PfEMP-1 proteins work in p. falciparum

Answer 4

P. falciparum parasites express a family of genes called var, which encode for a family of proteins, called PfEMP-1 (P. falciparum erythrocyte
membrane protein 1)

• These proteins are produced by the parasite and then exported outside of the parasite, carried through a network of intracellular membranous
  structures to the surface of the host red blood cell
• The PfEMP-1 proteins are pushed out by knob structures that extend out from the red blood cell surface. These are also created by Plasmodium-derived proteins
• PfEMP-1 proteins adhere to various host molecules on the surface of
  endothelial and other cells

Question 5

Why does P. falciparum sequesters itself deep in the microvasculature?

Answer 5

To escape the spleen!