Notes on Protozoa and Trypanosomiasis

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MICR7002: Immunology and Infectious Disease

• Course: Parasitology Module
• Topics: Protozoa, Helminths, Arthropods

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Protozoa

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Diversity of Protozoa

• Total Species: 65,000
  • Extant: 31,250
  • Extinct: 33,750
• Major Groups:
  • Flagellates: 6,900 species
  • Amoebae: 11,550 species
  • Sporozoa: 5,600 species
  • Ciliates: 7,200 species
• Lifestyle:
  • Free-living:
  • Flagellates: 5,100
  • Amoebae: 11,300
  • Sporozoa: 4,700
  • Ciliates: 1,800
  • Parasitic:
  • Flagellates: 250
  • Amoebae: all parasitic
  • Sporozoa: 2,500

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Key Protozoan Species

• Giardia spp.: 9 μm
• Trypanosoma spp.:
• Amoeba

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Protozoa: Flagellates

Characteristics:

• Presence of flagella
• Reproduce by binary fission
• Contains kinetoplasts (extranuclear DNA)
• Important species:
  • Trypanosoma cruzi
  • Trypanosoma brucei
• Habitat: Blood or tissue

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Image of Flagellate Protozoa

• Source: Lab Parasitologia-Hospital Dr. "Luis Calvo Mackenna"

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Protozoa: Amoeba

Characteristics:

• Usually unicellular and unstructured
• Exhibits ‘blebbing’ motion
• Can have multiple nuclei
• Important species:
  • Entamoeba histolytica
• Primarily found in the gastrointestinal system, but also in blood and tissue

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Protozoa: Sporozoa

Characteristics:

• Have a cyst-forming stage
• Majority belong to the Apicomplexa group
• Contains an apicoplast (plastid) and an apical complex for host penetration
• Important species:
  • Plasmodium spp. (malaria)
• Habitats: Blood and tissues

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Protozoa: Ciliates

Characteristics:

• Covered in cilia
• Important species:
  • Balantidium coli (only major human parasite of this type)
• Primarily found in gastrointestinal system, but can also be in blood and tissue

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Protozoan Case Study

• In-depth analysis of specific protozoan diseases

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Case Study: Trypanosomiasis

• Type: Flagellate protozoan
• Transmission: Arthropod vector
• Main species:
  • Trypanosoma brucei
  • Trypanosoma cruzi

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Structure of Trypanosoma spp.

• Includes unique structures:
  • Flagellar pocket
  • Nucleus
  • Kinetoplast, etc.

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Life Cycle of Trypanosomes

Stages:

• Promastigote
• Amastigote
• Trypomastigote
• Epimastigote
• Hosts: Vertebrate and invertebrate

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Trypanosoma brucei: African Trypanosomiasis

• Transmission via tsetse fly (Glossina spp.)
• Symptoms: Trypomastigotes in blood lead to neurological issues

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Life Cycle in Tsetse Fly

Stages of transformation inside tsetse fly’s gut

• Metacyclic trypomastigotes are injected into humans during blood meal

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Clinical Features of Trypanosoma brucei

• Two subspecies:
  • T. brucei gambiense: Slow disease progression
  • T. brucei rhodesiense: Rapid disease progression
• Infection leads to Chancre at bite site, CNS invasion, and sleep disturbances

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Morphology of T. brucei

Size range: 14 to 33 micrometers, contains key structures aiding movement and characteristics

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Pathophysiology of Sleeping Sickness

• Symptoms include cyclic fevers and neurological issues due to immune system interaction

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Immune Evasion Mechanisms

• Trypanosoma employs antigenic variation for evasion
  • Variable Surface Glycoprotein (VSG)

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Immune Response Types: TH1 versus TH2

TH1 Response:

• Targets intracellular parasites
• Mediated by IFN-γ, IL-2, TNF-β
  TH2 Response:
• Targets extracellular parasites
• Generates antibody-mediated response

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Antigenic Variation in Trypanosoma

• Significant aspect of parasitic evasion strategy, exploited through VSGs

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Recurrent Parasitaemia

• Overview of variations in immunogenic response over time

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Immune Configuration Over Infection Timeline

• Illustrated effects of recurrent parasitaemia introduced by Trypanosoma

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Antigenic Variation Continued

• Reinforces recurrent infections and fevers experienced by hosts

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Role of Autoantibodies in Infection

• Mechanism causing drop in Ig levels and links between parasite proteins and human cells

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Immune Evasion Strategies

• Continued focus on VSGs and Th1 response dynamics

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Cytokine Effects on Immune System

• Role in activating immune cells against infection

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Various Immune Evasion Mechanisms

• Retainment of antigenic variation effects in host adaptivity

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Overview of Complement System

• Assembly, activation, amplification, and attack on pathogens

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Immune Responses at the Site of Infection

• Initial local inflammation due to parasite entry and response stages

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Macrophage Dynamics During Infection

• Vast increase in macrophage activity and function in response to T. brucei infection

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Interaction of Kupffer Cells with Pathogens

• Importance of liver macrophages for parasite clearance

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Success of Antibody Responses

• Impact on trypanosome lysis and the implications for parasite survival

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Conceptual Understanding of Variation

• Comparison of responses and adaptations

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Trypanosoma cruzi: American Trypanosomiasis

• Overview of tryptomastigote transmission mechanisms

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Life Cycle of T. cruzi

• Overview detailing progression through vector and human stages

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Triatomine Bug Transmission Stages

• Lifecycle stages of T. cruzi in triatomine bugs

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Cycles of T. cruzi in Vectors

• Comparison to other parasites

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Morphology of T. cruzi

• Size and structural details

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Transmission Routes and Infections

• Detailing human transmission routes and implications

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Clinical Manifestations of Chagas Disease

• Primary symptoms and clinical observations

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Transmission Mechanics of the Reduviid Bug

• Description of infection pathways through fecal matter

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Symptoms of Chagas Disease

• Comprehensive list of symptoms presented over time

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Chronic Form of Chagas Disease

• Details of long-term progression and reactivation triggers

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Heart Transplant Reactions and Chagas Disease

• Study findings on reactivation post-heart transplant

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TLR Mediated Immunoreactions

• Focus on TLR roles in immune activation and challenges posed by parasites

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Immunoparasitology of Chagas Disease

• Complexity of stages and immune evasion techniques

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Immune Evasion via Macrophages

• Strategy of T. cruzi through macrophage fusion processes

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Pathways of T. cruzi Entry

• Summary of host entry mechanisms

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Persistence of T. cruzi in Tissues

• Long-term evasion of host immune response

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evasion of the Complement system

• T. cruzi methods to evade complement pathways

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Complement System Evasion Tactics

• Detailed mechanisms of avoiding complement-mediated destruction

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Cohesion of Host Interactions and Evasion

• Impact on therapy and infection management

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Th Responses and Chronicity

• Examination of immune profiles over chronic stages of infection

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Differences Between Antibody Responses

• Distinction between polyclonal and monoclonal response effectiveness

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Summary of T. brucei and T. cruzi

Comparison of key attributes and disease impacts:

• T. brucei: Africa, causes sleeping sickness; vector is tse-tse fly
• T. cruzi: South America, causes Chagas disease; vector is Reduviid bug

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Treatment Overview for Protozoan Infections

Common treatments for protozoan infections:

• Trypanosoma brucei: Arsenicals, Suramin
• Trypanosoma cruzi: Nifurtimox

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Australian Trypanosomes

Exploration of Australian animal hosts' susceptibility to Trypanosomes

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Contact Information & Resources

• Contact: Catherine.Gordon@qimrberghofer.edu.au
• CDC website and Australian Society for Parasitology links

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Assessment Information

• Quiz and exam details including format, content scope, and guidelines

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Assessment Overview

• Upcoming assessment dates and content focus

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Practice Questions

First question on cellular targeting by Trypanosoma cruzi