Sporozoan

• Sporozoan


  Morphologically distinct by the presence of a specialized complex of apical organelles including micronemes, rhoptries, polar ring, conoids and dense granules
• Classes of Sporozoa


  • Coccidea
• Orders of Coccidea


  • Eimeriida
  • Haemosporida
  • Piroplasmida
• Malaria


  "Mal" means bad and "aria" means air
• French army surgeon Alphonse Laveran was the first to discover the causative agent Plasmodium, in the red blood cell (RBC) of a patient in Algeria


  1880

  
• Golgi had described the asexual cycle of the malaria parasite in RBC

  
• Sir Ronald Ross described the sexual cycle of the malaria parasite in female Anopheles mosquito in Secunderabad, India


  1897

  
• Causative agents of malaria


  • Plasmodium vivax
  • Plasmodium falciparum
  • Plasmodium malariae
  • Plasmodium ovale
  • Plasmodium knowlesi

  
• Benign tertian malaria


  Caused by Plasmodium vivax

  
• Malignant tertian malaria


  Severe malaria caused by Plasmodium falciparum

  
• Benign quartan malaria


  Caused by Plasmodium malariae

  
• Ovale tertian malaria


  Caused by Plasmodium ovale

  
• Quotidian malaria


  Caused by Plasmodium knowlesi

  
• Other Plasmodium species are mainly of animal importance like P. cynomolgi, P. simium
• Hosts of Plasmodium life cycle


  • Female Anopheles (Anopheline) mosquito
  • Man

  
• Vectors of primary importance

  • Anopheline culicifacies in rural areas
  • A. stephensi in urban area
  • A. fluviatilis in hilly areas
  • A. minimus
  • A. philippinensis
  • A. sundaicus
  • A. maculatus
• Infective stage of Plasmodium


  • Sporozoites

  
• Modes of transmission


  • Bite of female Anopheles mosquito
  • Blood transfusion
  • Transplacental transmission

  
• Asexual cycles in human


  • Pre-erythrocytic schizogony
  • Erythrocytic schizogony
  • Gametogony
• Exflagellation


  1. Nucleus of the male gametocytes divides into eight flagellated actively motile bodies (microgametes)

  2. Microgametes protrude out as thread like filaments, lash out for some time and then, break free
• Zygote formation


  1. Fertilization occurs in about 30 minutes to 2 hours after the blood meal

  2. Within 24 hours, the nonmotile rounded zygote transforms into vermicular motile elongated form (ookinete)
• Oocyst formation


  Ookinete penetrates into the stomach wall of the mosquito and lies just beneath the basement membrane

  
• Sporozoite formation


  1. Sporogony to sporozoites: spindle shaped measuring 10–15 μm length with apical complex anteriorly

  2. Mature oocyst rupture and sporozoites are released then migrate to salivary gland
• Extrinsic incubation period


  Time taken for the parasite to develop in the mosquito vector before becoming infective to humans

  
• Extrinsic incubation period for different Plasmodium species


  • P. vivax—8–10 days
  • P. falciparum—9–10days
  • P. malariae—25–28 days
  • P. ovale—14–16 days

  
• Pre-erythrocytic schizogony


  1. Motile sporozoites leave the circulation within 30 minutes and enter liver

  2. Sporozoites become rounded and lose their apical complex and transform into trophozoites

  3. Schizogony transforms into pre-erythrocytic schizont containing several merozoites

  4. Merozoites are released outside on rupture and attack RBCs to perform erythrocytic schizogony

  5. Hypnozoites cause relapse of malaria after many years

  
• Erythrocytic schizogony


  1. Merozoites bind to the glycophorin receptors on RBC surface, enter by endocytosis and are contained within a parasitophorous vacuole inside the RBCs

  2. Merozoites round up, lose their internal organelle and transform into trophozoites

  3. Ring form appears with a central vacuole and peripheral thin rim of cytoplasm and a nucleus

  4. Late trophozoite becomes more irregular due to amoeboid movement

  5. Erythrocytic schizont undergoes multiple nuclear divisions and produces 6–30 daughter merozoites arranged in the form of rosette
• Number of merozoites per mature schizont for different Plasmodium species


  • P. vivax—12–24 (average 16)
  • P.falciparum—18–24 (average 20)
  • P. malariae—6–12 (average 8)
  • P. ovale—8–12 (average 8)
• Malarial paroxysm


  Periodic fever, chills and sweating associated with malaria
• Intraerythrocytic life cycle duration for different Plasmodium species

  • P. falciparum, P. vivax and P. ovale—48 hours
  • P. malariae—72 hours
  • P. knowlesi—24 hours

  
• Incubation period for different Plasmodium species

  • P. vivax—14 days (ranges 8–17 days)
  • P. falciparum—12 days (ranges 9–14 days)
  • P. malariae—28 days (ranges 18–40 days)
  • P. ovale—17 days (ranges 16–18 days)

  
• Stages of erythrocytic schizogony

  • Ring Form
  • Developing Schizont
  • Developing Trophozoites
  • Immature Schizonts
  • Mature Schizonts
• Gametogony


  1. Gametocytes (sexual forms) take place in the blood vessels of internal organs such as spleen and bone marrow

  2. Male gametocyte is smaller in size, lesser in number, their cytoplasm stains pale blue, and nucleus is larger, stains red and diffuse

  3. Female gametocyte is larger, numerous, their cytoplasm stains deep blue, nucleus is small, red and compact
• Duration for gametocyte development for different Plasmodium species


  • P. vivax—4–5 days
  • P. falciparum—10–12 days
  • P. malariae—11–14 days
  • P. ovale—5–6 days

  
• Morphology of gametocytes for different Plasmodium species


  • P. vivax
  • P. malariae
  • P. falciparum
  • P. Ovale
• Benign malaria


  • Characterized by a triad of febrile paroxysm, anemia and splenomegaly

  
• Febrile paroxysm


  Fever comes intermittently depending on the species, occurs every fourth day (72 hour cycle for P. malariae) and every third day (48 hour cycle for other three species), comprised of cold stage, hot stage and sweating stage
• Anemia in malaria


  Normocytic normochromic anemia due to parasite induced RBC destruction, splenic removal of infected and coated RBCs, bone marrow suppression and increased RBC fragility

  
• Splenomegaly


  Spleen gets enlarged and becomes palpable
• Falciparum malaria (Malignant Tertian malaria)


  • More acute and severe in nature with more complications than benign malaria, ability to sequester the parasites in the blood vessels of deep visceral organs like brain, kidney leading to blockade of vessels, congestion and hypoxia of internal organs