Intestional Protozoans - Part 1

Overview of Parasitology and Protozoans

  • Introduction to the heavy content in parasitology

    • Focus on protozoans; largest portion with many organisms

    • Lectures divided into two parts for easier digestion

Definition of Protozoans

  • Protozoans are unicellular eukaryotic organisms

    • Transition from previous focus on prokaryotic organisms

    • Characteristics of eukaryotic organisms include specialized organelles not found in prokaryotes

    • Specialized organelles facilitate life functions

Reproduction of Protozoans

  • Many protozoans reproduce via binary fission

    • One cell divides into two daughter cells

Distribution of Protozoans

  • Protozoans have a worldwide distribution

    • Commonly found in tropical areas

    • Certain types are evenly distributed population-wise

Classification of Protozoans

  • Five types of protozoans to discuss:

    1. Amoeba

    • Shape-changing organisms

    • Move using pseudopods

    • Can exist in infective cyst form

    • Ingest food via phagocytosis (no mouth present)

    1. Flagellates

    • Possess one or more flagella

    • Can be free-living or parasitic

    • Example: Giardia

    1. Ciliates

    • Possess cilia for movement, attachment, and feeding

    • Typically consume bacteria and algae

    1. Coccidia

    • Less detailed discussion

    1. Microsporidia

    • Less detailed discussion

Intestinal Protozoans

  • Focus on clinically relevant intestinal protozoans

    • Discussion of both pathogenic and non-pathogenic organisms

    • Importance of differentiation for accurate diagnosis

Amoebae

Characteristics

  • Presence of pseudopodia

    • Pseudopodia defined:

    • Pseudo: false, Pod: feet (false feet)

  • Types of amoebae:

    • Free living

    • Pathogenic

    • Non-pathogenic

  • Found in intestinal tract and other bodily areas

Stages of Amoebae

  1. Cyst Form

    • Indicates inactive infection or carrier state

    • Rigid structure; non-motile

    • Found in formed stool; infective form

  2. Trophozoite Form

    • Pleomorphic and motile

    • Represents active feeding form; seen in loose/watery stools

Characteristics Considered in Identification

  • Size: Measured using a micrometer

  • Shape: Pyriform, oval, round

  • Motility: Observe wet prep samples

  • Number of nuclei:

    • Immature cyst: 1-2 nuclei

    • Mature cyst: 4-8 nuclei

  • Cariesome:

    • Chromatin material in mitotic division

    • Dense mass; different from nucleolus

  • Peripheral nuclear chromatin:

    • Dark dense mass around nucleus

  • Cytoplasm appearance:

    • Vacuolated, ingestion of debris, red blood cells, glycogen vacuoles

Specific Amoeba: Entamoeba histolytica

  • Highly pathogenic organism

  • Causes amoebic colitis and extraintestinal abscesses

  • global presence, especially in poorly sanitized areas

  • Kills over 100,000 people annually

Amoebic Colitis

  • Gradual onset (1-2 weeks)

  • Distinct from bacterial dysentery

Extraintestinal Abscesses

  • May occur in liver

  • Caused by trophozoites invading tissue

  • Results in necrosis; contact-dependent cell destruction

  • Destructive process termed trobocytosis

    • Mechanism includes adherence to mucosa and cell degradation

Symptoms and Diagnosis

  • Asymptomatic case can lead to carrier state

    • Negative to weak antibody titer

    • No blood in stool, possible presence of cysts

  • Symptoms can mimic ulcerative colitis

    • Dysentery characterized by 10+ bowel movements/day

    • Fever absent in many cases

  • Extraintestinal spread leads to upper right abdominal pain, tenderness, fever

Life Cycle and Transmission

  • Fecal-oral transmission via infective cysts

    • Contaminated food/water, fomites, sexual practices

    • Mechanical transmission by flies/cockroaches

Diagnostic Techniques

  • Use of Ova and Parasite Preparation (ONP)

    • Essential for identification

    • Permanent smear (trichrome stain) crucial

    • Collect three specimens over 10 days

  • Other methods: antigen detection, histology, PCR, serology (rare)

Microscopic Characteristics of Entamoeba histolytica

  • Motility: Rapid and unidirectional but rare in samples

  • Cytoplasm: finely granular appearance

  • Karyosome: centrally located

  • Red blood cells present in cytoplasm (diagnostic feature)

Distinguishing Characteristics

  • Trophozoite size: 12 to 60 micrometers

  • Progressive rapid movement observed in some cases

  • Cytoplasm: ground glass appearance with ingested red blood cells

  • Cyst shape: spherical

    • Mature cysts: up to 4 nuclei

    • Immature cysts: 1-2 nuclei

    • Chromatoid bars with rounded ends, possible glycogen masses

Prevention Strategies

  • Humans as reservoir host; transmission to various mammals

  • Cysts can survive in suitable conditions for up to 60 days

  • Importance of water treatment, sanitation, proper food preparation

  • Avoiding human waste as fertilizer and unprotected sexual practices