T. cruzi

• Trypanosoma cruzi


  Causative agent of Chagas disease

  
• American Trypanosomiasis


  Chagas Disease
• Vector


  • Reduviid bugs (Triatoma, Panstrongylus, Rhodnius)
• Infective Stage


  Metacyclic trypomastigote

  
• Diagnostic Stages


  • Blood Smear: Trypomastigote
  • Tissue biopsy: amastigote

  
• Multiplication


  1. Human: Binary fission as amastigote

  2. Vector: Longitudinal fission as epimastigote
• Reservoir host


  • Domestic animals, armadillo, racoons, rodents, marsupials, some primates
• Infection


  Intracellular: Myocytes, cells of reticuloendothelial system, skin, gonads, intestinal mucosa, placenta
• Triatoma


  • Dark brown to black with small tan edge around abdomen, wings held flat over back, 4 segmented antennae, 3 segmented beak extending backward below body, found in squalid houses or with thatched roof
• Triatomine


  Kissing Bug, Reduviid Bug - tends to bite the face of the host
• Forms in the Life Cycle of Trypanosoma cruzi


  • Amastigote
  • Epimastigote
  • Trypomastigote

  
• Amastigote


  • Round or ovoid in shape, 1.5 – 4 um diameter, in small groups of cyst-like collections in tissue, intracellular in humans, replicating form in human host, no exterior flagella and undulating membrane, movement is just rotation, found in macrophages and myocardium

  
• Trypomastigote


  • Unique C, S or U-shaped, motile but has no replicative capability, infective to both humans and vectors, extracellular infective, pointed posterior end, undulating membrane with 2 – 3 undulations, single threadlike flagellum originating near the prominent kinetoplast

  
• Epimastigote


  • Present in the midgut of vector, motile, presenting intense replicative activity by longitudinal binary division, kinetoplast anterior to the nucleus
• Life Cycle of Trypanosoma cruzi

  1. Starts when a triatomine reduviid bug bites a human host while defecating with metacyclic trypomastigote (infective stage to humans) in the feces and enters through the bite wound or mucosal membrane

  2. Metacyclic trypomastigote enters the circulation but does not multiply, can be ingested by macrophages or infect cells like myocardium

  3. Intracellularly, it transforms to become an amastigote and will undergo replication by binary fission

  4. The amastigote would then transform to become a blood trypomastigote and will be released extracellularly to the blood circulation

  5. The blood trypomastigotes can infect another cell and transform to become amastigote intracellularly and will multiply and repeat the cycle, or be ingested by an insect vector

  6. Once ingested by the triatomine bug, it will pass through the posterior portion of the midgut and will transform to become epimastigote

  7. The epimastigote will multiple in the midgut through longitudinal binary fission

  8. It will then transform to become a metacyclic trypomastigote once it is in the hindgut, and will be released through fecal material to gain entry to the human host

  9. The cycle will continue

  
• Infective stage to humans


  Metacyclic trypomastigote

  
• Infective stage to vector


  Blood trypomastigote
• Diagnostic stages


  • Amastigote (tissue biopsy)
  • Trypomastigote (blood smear)

  
• The image shows how the triatomine bug bites and defecates and how Trypanosoma gains entry to the human host