Malaria

• 3 Forms of Plasmodium:

  1. Sporozoite > In Mosquitos and Liver
  2. Trophozoite > In RBC
  3. Merozoite > In blood but not RBC
• Chain of Infection: Organism: Plasmodium Parasites; 5 strains (p.flaciparum and Vivax) common.
• Reservior: Humans (reptiles, birds, mammals) and Mosquitos
• Vector: Anopheles mosquito.
• Transmission: Indirect through mosquito
• Portal of Exit/Entry: Insect bite.
• Susceptible Host: Anyone with no prior exposure.
• Characteristics of Anopheles Vector: There are 400 types of mosquito but only 30 species are known vectors for malaria.
• Anopheles mosquito bites between dusk and dawn.
• Anopheles mosquito lays eggs in aquatic habitats.
• Anopheles mosquito larvae eat blood to grow.
• Characteristics of Plasmodium spp.: Plasmodium spp. are Protists, which are unicellular, eukaryotic, and obligate parasites that harm the host.
• Plasmodium spp. are Apicomplexans, a group of organisms with specialized structures in their infectious agent cell.
• Mitochondria are a specialized structure in the infectious agent cell of Plasmodium spp.
• Rhoptry is an organelle that contains parasite proteins involved in invading, modifying host cell of Plasmodium spp.
• Micronemes contain proteins required for motility, recognizing and binding host cell of Plasmodium spp.
• Dense Granule is a secretory granule that contains proteins that modify parasitophorous vacuole membrane of Plasmodium spp.
• Apicoplast is derived from red algae through endosymbiosis and Plasmodium spp. have various metabolic pathways, including heme biosynthesis pathway.
• 2 Types of Schizogony

  • Tissue > Liver
  • Exoerythrocytic > Blood
• 2 hosts of Plasmoidum 

  • Primary host = Anopheles mosquito -Definitive host, Where plasmodium reaches sexual maturity
  • Secondary host = Vertebrates (birds, lizards etc).
• Sporozoites are injected in mosquito saliva during a bite.
• The motile infective form of Plasmodium spp. is known as a sporozoite.
• Sporozoites infect hepatocytes.
• In the hepatocyte, the sporozoite undergoes tissue schizogony, increasing in size and replicating its nucleus and other organelles many times.
• The sporozoite forms a schizont, a large multinuclear cell.
• Cytokinesis creates multiple daughter cells within the schizont.
• Merozoites, thousands per hepatocyte, are released into the blood when the hepatocyte ruptures.
• Merozoites attach to and infect red blood cells in the blood stream.
• In the red blood cell (erythrocyte), the merozoite develops into a trophozoite.
• The mature trophozoite undergoes blood schizogony, causing the schizont to rupture and release more merozoites.
• From 8 to 24 merozoites per erythrocyte are released during blood schizogony.
• Some merozoites develop into gametocytes in the red blood cell.
• Gametocytes stay in the blood stream waiting for a mosquito to ingest them.
• Merozoites in the red blood cell circulate through the spleen, which is part of the immune system, and detect infection and damage to cells.
• P.falciparum produces proteins on the surfaces of infected red blood cells, causing adhesion to blood vessel walls and decreasing passage through the spleen.
• Merozoites digest hemoglobin and release the heme group and a heterocyclic porphyrin ring containing iron, which is toxic to merozoites and so converted to an insoluble crystalline form, hemozoin.
• Mosquitoes ingest gametocytes in the midgut and finish developing into gametocytes.
• Microgametes or macrogametes are produced during fertilization, forming a zygote.
• The zygote develops into a motile ookinete, which penetrates the mid gut wall and becomes an oocyst.
• The oocyst divides, producing sporozoites, which travel to the salivary glands and are injected into the secondary host during the next blood meal.