protozoa

Protozoa Overview

Definition

  • Protozoa are one-cell eukaryotic organisms.

Categories of Protozoa

  • Major Groups (distinguished by locomotory structures and reproductive mechanisms):

    • Amoebae

      • Example: Entamoeba histolytica

    • Ciliates

      • Example: Balantidium coli

    • Flagellates

      • Examples: Giardia lamblia, Trichomonas vaginalis

    • Apicomplexa

      • Examples: Toxoplasma gondii, Plasmodium spp.

    • Coccidia

      • Example: Cryptosporidium

    • Microspora

      • Example: Nosema

Life Cycle of Protozoa

Trophic Forms

  • Trophozoite

    • Active, motile, capable of reproduction.

  • Cyst

    • Resistant, non-motile, unable to grow and multiply.

    • Can be infective to humans.

Specific Protozoa

1. Entamoeba histolytica

  • Causes amoebic dysentery.

  • Can lead to extraintestinal infections (e.g., liver abscess) in rare cases.

  • Other related species:

    • Entamoeba coli

    • Entamoeba hartmanni

    • Entamoeba gingivalis (non-pathogenic)

Diagnostic Methods

  • Specimens:

    • Stained preparations

    • Consecutive stool samples (over 10 days)

    • Tissue biopsy

    • Aspirate from extraintestinal abscesses

    • Direct methods (wet mount, staining)

Characteristics

  • Trophozoites: 12-40 μm, motility through pseudopods.

  • Cysts: 5-20 μm, can have multiple nuclei.

  • Differentiation from other species:

    • E. histolytica: ingests erythrocytes.

    • E. coli: does not ingest erythrocytes but may ingest other substances.

2. Trichomonas vaginalis

  • No cyst form, exists only as trophozoite.

  • Microscopically observed through wet mounts or Giemsa stain.

  • Diagnostic specimens include vaginal swabs, urethral secretions, and urine.

Characteristics

  • Trophozoite: 10-12 μm long, pear-shaped with a single nucleus, and motility from flagella.

  • Diagnosis: Can be made via liquid media cultivation and molecular diagnosis (PCR).

3. Giardia lamblia

  • Life cycle includes two stages: trophozoite and cyst.

  • Trophozoite: 9-21 μm, pear-shaped, bilaterally symmetrical with two nuclei and a suction disc for attachment.

  • Cyst: oval and thick-walled with up to four nuclei.

Diagnostic Methods

  • Specimens:

    • Direct examination of stool samples (3-day collection).

    • Immunodiagnostic tests and molecular methods (PCR).

4. Toxoplasma gondii

  • Definitive host: cats; humans can get infected through oocysts found in cat feces or through undercooked meat.

  • Spread can also occur from mother to child during pregnancy.

Life Cycle & Symptoms

  • Stages include tachyzoites, merozoites, bradyzoites (tissue cysts), and sporozoites (oocysts).

  • Symptoms may be mild or absent in healthy individuals but can cause severe complications in immunocompromised patients.

Diagnostic Methods

  • Specimens include blood and CSF.

  • Diagnosed through serological tests (e.g., IgM, IgG) and PCR.