Protozoa

• Plasmodium spp.


  Protozoa that cause malaria
• Toxoplasma gondii


  Protozoa that cause toxoplasmosis
• Malaria is one of the most common infectious diseases and a leading cause of death, especially among African children

  
• Plasmodium life cycle


  • Sexual cycle in mosquitoes (sporogony), asexual cycle in humans (schizogony)
  • Sporozoites introduced into human blood by mosquito bite
  • Infect liver cells, then red blood cells
  • P. vivax and P. ovale have latent liver stage (hypnozoites)
  • Merozoites released from liver and red blood cells, infect more red blood cells

  
• Malaria symptoms


  • Periodic release of merozoites causes recurrent chills, fever, and sweats
• P. falciparum malaria


  • More severe, infects more red blood cells, causes capillary occlusion, cerebral malaria, hemoglobinuria, acute renal failure

  
• Quartan malaria


  Caused by P. malariae, recurs every 4 days

  
• Tertian malaria


  Caused by P. vivax, P. ovale, P. falciparum, recurs every 3 days

  
• Malignant malaria


  Caused by P. falciparum
• Benign malaria


  Caused by P. vivax, P. ovale
• Malaria lab diagnosis


  1. Microscopic examination of thick and thin blood smears

  2. PCR or ELISA if blood smears inconclusive
• Toxoplasma life cycle


  • Definitive host is domestic cats, humans are intermediate hosts
  • Infection from ingesting cysts in undercooked meat or accidental contact with cat feces
  • Tachyzoites invade cells, then form slow-growing bradyzoite cysts
  • Cats ingest cysts, release bradyzoites that form oocysts excreted in feces

  
• Toxoplasmosis lab diagnosis


  1. IgM antibody test for acute/congenital infection

  2. Microscopic examination for trophozoites and cysts

  3. Cell culture or mouse inoculation
• Toxoplasma gondii


  A type of protozoa that causes toxoplasmosis
• Protozoa


  A group of eukaryotic microorganisms that are typically single-celled
• Toxoplasmosis


  A disease caused by Toxoplasma gondii protozoa
• Leishmania sp.

  Genus of parasitic protozoa that cause leishmaniasis

  
• Leishmania sp. includes four major pathogens: Leishmania donovani, Leishmania tropica, Leishmania Mexicana, and Leishmania braziliensis
• Leishmania donovani


  • Causes kala-azar (visceral leishmaniasis)
  • Life cycle involves sand fly as vector and mammals as reservoirs
  • Female sand flies are vectors as they take blood meals for egg maturation
  • Promastogotes transform into amastigotes in human macrophages and can prevent fusion with lysosomes

  
• Leishmania tropica, Leishmania mexicana, Leishmania braziliensis, Leishmania major

  • Cause cutaneous leishmaniasis (L. tropica, L. mexicana, L. major) or mucocutaneous leishmaniasis (L. braziliensis)
  • Sandflies are the vectors and forest rodents are the reservoirs
  • Life cycle is similar to L. donovani