Protozoans

19.1: Protozoans

Introduction to Protozoans

  • Definition: Protozoans are unicellular eukaryotic microorganisms in the Kingdom Protista.

  • Reproduction:

    • Asexual reproduction methods:

      • Fission: One cell splits into two.

      • Schizogony: Multiple fission; nucleus divides multiple times.

      • Budding: Pinching off a bud from a parent cell.

    • Sexual reproduction via fusion of haploid sex cells (gametes).

  • Trophozoite: The vegetative form that is motile, feeding, and reproducing.

  • Cyst Formation: Under harsh conditions, protozoans can form cysts, aiding survival outside hosts; this leads to exystation and reverts to trophozoite in favorable conditions.

Classification of Parasitic Protozoans

Protozoans are categorized based on their locomotion methods:

1. Sarcomastigophora (Amoeboflagellates)

  • Movement: Via pseudopodia (amoebas) and flagella.

  • Amoebas (Subphylum Sarcodina):

    • Move by extending cytoplasm (pseudopodia).

    • Obtain food through phagocytosis.

    • Pathogen Example: Entamoeba histolytica (causes amoebic dysentery).

      • Transmission: Fecal-oral route via contaminated food/water.

      • Symptoms: Ulceration of intestines, potential liver invasion, diagnosed by identifying cysts in fecal smears.

    • Acanthamoeba: Infects eyes and CNS via waterborne cysts.

2. Flagellates (Subphylum Mastigophora)

  • Movement: By flagella and sometimes undulating membranes.

  • Pathogens:

    • Trypanosoma gambiense and T. rhodesiense: Cause African sleeping sickness (African trypanosomiasis).

      • Transmission: Via tsetse fly bites.

      • Diagnosis: Microscopic examination for Trypanosoma in blood or lymph fluid.

    • T. cruzi: Causes Chagas' disease, transmitted by Triatomid bugs.

    • Giardia lamblia: Causes giardiasis, common intestinal disease in the U.S.

      • Transmission: Fecal-oral route, diagnosed through fecal smears.

More Protozoan Pathogens

3. Trichomonas vaginalis

  • Disease: Genitourinary trichomoniasis.

  • Statistics: Estimated 2.5 million cases annually in the U.S.

  • Symptoms: Vaginitis in females, often asymptomatic in males, diagnosed by viewing trophozoites in discharge/urine.

4. Ciliophora

  • Features: Cilia for movement and food intake.

  • Pathogen: Balantidium coli, causing balantidiasis.

    • Transmission: Fecal-oral route, leading to intestinal ulceration; diagnosed by microscopically looking for B. coli in fecal smears.

5. Apicomplexans (Sporozoa)

  • Movement: Non-motile in mature form; complex life cycles.

  • Pathogens:

    • Toxoplasma gondii: Causes toxoplasmosis, poses risks in pregnant women and immunocompromised individuals.

      • Transmission: Consumption of raw meat or exposure to cat feces.

    • Plasmodium (P. falciparum, P. malariae, P. ovale, P. vivax): Causes malaria, transmitted by Anopheles mosquitoes.

      • Life Cycle: Asexual reproduction in liver/red blood cells; sexual reproduction in mosquitoes.

      • Diagnosis: Identification of parasites in red blood cells via microscopy.

    • Cryptosporidium: Causes diarrhea; of particular risk to immunocompromised individuals; transmitted via fecal-oral route.

19.1: Protozoans

Introduction to Protozoans

Definition: Protozoans are single-celled (unicellular) microorganisms that have a defined nucleus (eukaryotic) and belong to the Kingdom Protista.

Reproduction

  • Asexual Reproduction: This is a process where one organism can reproduce without a partner, using methods such as:

    • Fission: One cell splits into two cells.

    • Schizogony: A type of multiple fission where the nucleus divides multiple times before the cell splits.

    • Budding: A small part of the parent cell pinches off to become a new cell.

  • Sexual Reproduction: This involves the joining of two specialized cells (haploid sex cells or gametes) to form a new organism.

  • Trophozoite: The active and feeding form of protozoans that can move and reproduce.

  • Cyst Formation: In harsh conditions, protozoans can form thick protective shells (cysts) to help them survive outside their hosts. When conditions improve, they can revert to the active trophozoite form.

Classification of Parasitic Protozoans

Protozoans are classified based on how they move:

  1. Sarcomastigophora (Amoeboflagellates)Movement: They move using extensions of their cell body, called pseudopodia, or using whip-like structures known as flagella.

    • Amoebas (Subphylum Sarcodina):

      • Move by extending their cytoplasm (pseudopodia).

      • Feed by engulfing (phagocytosis) food particles.

      • Example: Entamoeba histolytica causes amoebic dysentery, transmitted through contaminated food/water. Symptoms include intestinal ulceration and can be identified by spotting cysts in stool samples.

      • Acanthamoeba: Infects the eyes and nervous system (CNS) through contaminated water.

  2. Flagellates (Subphylum Mastigophora)Movement: They use flagella or sometimes undulating membranes to move.

    • Pathogens:

      • Trypanosoma gambiense and T. rhodesiense: Cause African sleeping sickness, transmitted by tsetse flies. Diagnosis involves examining blood or lymph fluid under a microscope.

      • T. cruzi: Causes Chagas' disease, spread by kissing bugs.

      • Giardia lamblia: Causes giardiasis, a common intestinal illness in the U.S., transmitted via the fecal-oral route, diagnosed through stool samples.

  3. Trichomonas vaginalis

    • Disease: Causes a genital infection known as trichomoniasis.

    • Statistics: Approximately 2.5 million cases in the U.S. annually.

    • Symptoms include vaginitis in females, while males usually show no symptoms. Diagnosis is through examining samples for trophozoites in urine or discharge.

  4. Ciliophora

    • Movement and Features: Move using tiny hair-like structures called cilia and can also use cilia to take in food.

    • Pathogen: Balantidium coli, which causes balantidiasis, transmitted through contaminated food/water, leading to intestinal ulcers. Diagnosis involves microscopy to find B. coli in stool samples.

  5. Apicomplexans (Sporozoa)

    • Movement: They are non-motile in the mature (adult) form and have complex life cycles.

    • Pathogens:

      • Toxoplasma gondii: Causes toxoplasmosis, particularly risky for pregnant women and those with weak immune systems, transmitted via raw meat or cat feces.

      • Plasmodium species (e.g., P. falciparum, P. malariae): Causes malaria, spread by Anopheles mosquitoes. Life cycle involves asexual reproduction in the liver/red blood cells and sexual reproduction in mosquitoes. Diagnosis is done by identifying parasites in red blood cells under a microscope.

      • Cryptosporidium: Causes diarrhea and poses risks to immunocompromised individuals, spread via the fecal-oral route.

Trichomonas vaginalisDisease: Causes a genital infection known as trichomoniasis.Statistics: Approximately 2.5 million cases in the U.S. annually.Symptoms: Includes vaginitis in females, while males usually show no symptoms. Diagnosis is through examining samples for trophozoites in urine or discharge.