Practical Session in Parasitology: Genus Entamoeba and Genus Balantidium Notes

General Introduction to Subkingdom Protozoa

• Etymology: The word "Protozoa" is derived from the Greek terms "protos" meaning first and "zoon" meaning animal.

• Biological Definition:

  • A Protozoan is a single cell that functions as a single organism.

  • These are single-cell eukaryotes.

• Vital Functions:

  • Feeding.

  • Breathing.

  • Excretion.

  • Movement.

  • Reproduction.

• Cellular Organelles:

  • Nucleus and Cytoplasm: The cytoplasm is divided into ectoplasm and endoplasm.

  • Protective Shell: Known as the pellicle or cuticle.

  • Nutrition Apparatus: Includes the cytostomy, cytopharynx, and digestive vacuoles.

  • Movement Apparatus: Includes an undulating membrane, fringes, whips, and pseudopods.

  • Excreta: Waste products are managed via the shrinking vacuole.

  • Skeleton: Supported by the axostyle.

• Reproduction Methods:

  • Asexual: Occurs through division or budding.

  • Sexual: Occurs through conjugation.

Taxonomy and Classification of Protozoa

• Kingdom: Animalia.

• Subkingdom Metazoa: Multicellular organisms.

• Subkingdom Protozoa: Single-cell eukaryotes.

• Phylum Sarcomastigophora:

  • Subphylum Sarcodina: Includes the Genus Entamoeba.

    • Species: Entamoeba histolytica (or histolyca), Entamoeba coli, Entamoeba hominis, Entamoeba gingivalis.

  • Subphylum Mastigophora.

• Phylum Apicomplexa:

  • Subphylum Haemosporidia.

  • Subphylum Coccidia.

• Phylum Ciliophora:

  • Subphylum Ciliophora: Includes the Genus Balantidium.

    • Species: Balantidium coli.

  • Class Infusoria.

Genus Entamoeba: Entamoeba histolytica

• Global Significance: Ranked 3rd in mortality among parasitosis, following malaria and schistosomiasis. It is found everywhere in the world, particularly in tropical areas.

• Morphological Forms:

  • Cyst: The invasive form. The mature cyst has 4 nuclei. It possesses a double shell that provides stability in the external environment. It is excreted in feces and is capable of invasion.

  • Trophozoite (Vegetative Form): The form that actively reproduces, moves, and feeds. It has two sub-types:

    • Forma magna: Pathogenic; fast-moving; characterized as an erythrophage (feeds on red blood cells).

    • Forma minuta: Non-pathogenic; slow-moving; feeds on bacteria.

• Detailed Morphology of Forma Magna:

  • Size Range: $15 - 40\,(60)\,\mu m$.

  • Internal Structures: Pseudopodium, ectoplasm, endoplasm, ribosomes.

  • Vacuoles: Food vacuoles containing bacteria or Red Blood Cells (RBCs).

  • Nucleus: Cartwheel-shaped nucleus with a nucleolus/karyosome.

• Cyst Comparison:

  • Entamoeba histolytica cyst: Contains 4 nuclei.

  • Entamoeba coli cyst: Size range $8 - 35\,\mu m$ (average $12 - 25\,\mu m$); contains 8 nuclei, eccentric karyosome, uneven peripheral chromatin, and chromatoid bars.

Amebiasis: Pathogenesis, Clinical Picture, and Diagnosis

• Pathogenesis Factors:

  • Histolysin.

  • Lipophilic protein.

  • Phospholipase.

  • Trogocytosis: A process mentioned in the context of tissue destruction.

• Clinical Picture:

  • Prolonged diarrhea.

  • Inflammation of the colon lining (ulcerative colitis).

  • Mucous-bloody stools.

  • Abdominal pain and fatigue.

  • Fever (temperature).

  • Acute peritonitis.

• Life Cycle/Study Points:

  • Definitive host: Humans.

  • Intermediate host: None (direct life cycle).

  • Invasive form: Mature cyst with 4 nuclei.

  • Pathogenic form: Forma magna.

  • Mode of infection: Fecal-oral (ingestion of cysts).

  • Localization: Intestine (colon).

  • Parasitosis name: Amebiasis.

• Diagnosis:

  • Presence of cysts and forma magna in fresh feces (quadruple cysts).

  • Serological tests to detect histolysin.

Other Species of Entamoeba and Related Notes

• Entamoeba hominis:

  • While many are asymptomatic carriers, it is linked to chronic diarrhea and IBS-like symptoms in some individuals. It is regarded as a potential pathogen (associated with Blastocystis hominis in some contexts).

• Entamoeba gingivalis: Associated with leucocytes in morphological studies.

• Entamoeba coli and Obesity: There is a positive association between intestinal parasitic infections and obesity. Moderate or severe infection with E. coli can contribute to excessive fat deposition and long-term harmful effects on health.

• Ocular Pathogens: Certain amoebas can reach the cornea of the eye, leading to permanent vision damage and blindness.

Genus Balantidium: Balantidium coli

• General Characteristics: The only ciliated parasite found in humans. Distributed globally, specifically noted in Central and South America and New Guinea.

• Morphology of the Vegetative Form:

  • Cilia: Used for movement.

  • Nuclei: Contains both a Macronucleus and a Micronucleus.

  • Nutrition/Excretion: Pellicle, vestibule, cytostome, food vacuoles, contractile vacuole, and cytopyge (cytopyge for waste).

  • Cytoplasm: Differentiated into layers.

• Pathogenesis - Balantidiasis:

  • Employs hyaluronidase to invade the intestinal submucosa.

• Clinical Picture:

  • Diarrhea.

  • Rare inflammatory processes and ulcerative manifestations.

  • Rarely muco-bloody stools.

  • Nausea and vomiting.

  • Fatigue and fever (temperature).

• Diagnosis:

  • Detection of cysts and vegetative forms in feces (coprological test).

  • Cultivation techniques.

  • Note: There are no immunological tests available for this parasite.

Practical Session Requirements

• Objective: Identification of the following forms:

  • Entamoeba histolytica: f. magna.

  • Entamoeba histolytica: cyst.

  • Entamoeba histolytica: f. minuta.

  • Balantidium coli: vegetative form.

  • Balantidium coli: cyst.

• Study Guide Outline: Students must identify 12 points for each species:

  1. Latin name (species name).

  2. Morphological forms.

  3. Cell cycle.

  4. Mode of infection.

  5. Invasive form.

  6. Pathogenic form.

  7. Definitive host.

  8. Intermediate host.

  9. Parasitosis name (Latin name + -asis/-osis).

  10. Pathogenesis.

  11. Clinical picture.

  12. Diagnosis.