PHYLUM-RHIZOPODA

Previously known as Sarcomastigophora.
Contains ~200 species, including amoebas.
Most are free-living or commensal; includes important parasites (e.g., Entamoeba histolytica).
"Rhizopoda" means "root-like foot," referring to cytoplasmic flow forming pseudopodia (false feet).
Used for movement and capturing food via phagocytosis, trapping food in vacuoles.
Some amoebas exhibit complexity beyond primitive structures.

Human parasite with uncertain transmission in primates.
Causes amoebic dysentery—a serious inflammatory disorder of the intestines.
Symptoms include severe diarrhea, abdominal pain, and fever.
Historical significance: referred to as the "handmaiden of war," impacting greater casualties than warfare.
Commonly found in unsanitary living conditions, often during conflicts and migrations.

E. histolytica infects ~10% of the global population, often asymptomatically.
Includes three species: E. histolytica (pathogenic), E. dispar (usually harmless), and E. moshkovskii (pathogenicity unclear).
Variability in E. histolytica strains affects pathogenicity.
Virulent strains show over-expression of genes like KERP1, linked to disease severity.
Infections lead to millions of cases and 40,000-110,000 annual deaths worldwide.

Key Characteristics:
- Lacks contractile vacuole and mitochondria but has mitochondrial genes.
- Presence of mitosomes—remnants of mitochondria.
Two main stages:
- Trophozoite Stage: Actively growing and feeding.
- Cyst Stage: Transmission stage, essential for survival and spread.

Size: 12-60 µm.
Structure:
- Clear, granular outer cytoplasm; densely granular inner cytoplasm.
- Centrally located karyosome indicating aggregated chromatin.
Reproduces asexually through cell division.
Cyst transformation stimuli are uncertain.
Can cause flask-shaped ulcers in intestines during virulence.

Size: 10-15 µm in diameter.
Structure includes:
- Four nuclei in mature cysts.
- Chromatoidal bodies serve as nucleoprotein storage.
- Chitin cell wall allows survival in the environment.
Transmission:
- Fecal-oral route via flies, fingers, food, water, and possibly contact with dogs.
- Infective cysts turn into eight trophozoites in the small intestine.

Avirulent strains: Remain in the intestinal lumen without harm.
Virulent strains:
- Invade gut wall, creating flask-shaped ulcers.
- Symptoms include gastric pain, mucus, blood in stools, dehydration.
- Ulcer formations may lead to severe complications, including potential death.

Entamoeba dispar:
- Morphologically identical to E. histolytica but typically non-pathogenic.
- Important for accurate diagnosis to avoid unnecessary treatment.
Entamoeba moshkovskii:
- Free-living amoeba; may infect humans but often misconceived in reports.
- Likely leads to under-reporting of cases due to diagnostic challenges.
Entamoeba gingivalis:
- Found in the mouth; transmitted through kissing and sharing utensils.
- Linked to periodontitis and infections across various body parts.

Habitat: Free-living in warm water bodies.
Life Cycle:
- Trophozoite Stage: Infective stage through the nasal cavity.
- Flagellate Form: Formed under stress (non-infective).
- Cyst Form: Dormant stage; not infective.

Known for causing fatal encephalitis.
Can enter through skin wounds or organ transplants.
Causes chronic disease with high mortality; potentially accesses the brain via the choroid plexus.

Exists in soil and freshwater; opportunistic pathogens.
Infections occur via skin wounds or inhalation of cysts, particularly in immunocompromised hosts.
Associated with keratitis from contaminated contact lenses.

Understanding these amoebae's life cycles, pathogenicity, and transmission routes is crucial for prevention and management of infections.