Parasitic Protozoa Notes

Chapter 23: Parasitic Protozoa Part 1

General Characteristics

  • Focus on parasitic protozoa.
  • Covers ciliated protozoa and amoeba.

Introduction to Protozoa

  • Of the 20,000 species of protozoa, less than 20 genera cause disease.
  • Significant worldwide impact regarding the number of cases:
    • Malaria: 150 million cases (some sources cite 300-500 million).
    • Trypanosomiasis: 8 million cases.
    • Leishmaniasis: 12 million cases.
    • Amoebiasis: 500 million cases.

Protozoa: General Characteristics

  • Eukaryotic chemoheterotrophs.
  • Usually motile.
  • Classified under Kingdom Protista.
  • Habitat: water and soil, requiring a liquid-rich environment.
  • Trophozoite: feeding and growth stage; consumes bacteria, small nutrients, and sometimes human red blood cells (RBCs).
  • Cyst: dormant, resistant stage; functions as the infective stage.

Four Groups of Protozoans (Based on Locomotion)

  • Ciliates: motile via cilia.
  • Flagellates: motile via flagella.
  • Amoebae: move using pseudopods.
  • Apicomplexans: non-motile; all are parasitic.

Ciliates

  • Move via cilia.
  • Balantidium coli causes severe dysentery (balantidiasis).
  • Transmission: oral-fecal contamination, particularly from pigs.
  • Only one human parasite: Balantidium coli.
  • Key features of Balantidium coli:
    • Cyst form.
    • Trophozoite form.
    • Dumbbell-shaped nucleus.

Dysentery

  • Inflammatory disorder of the intestine, especially the colon.
  • Symptoms: severe diarrhea containing mucus and/or blood, fever, and abdominal pain.
  • If untreated, dysentery can be fatal.
  • Types of Dysentery:
    • Bacillary dysentery (Shigella).
    • Balantidium dysentery (Balantidium coli).
    • Amoebic dysentery (Entamoeba histolytica).

Amoebae

  • Examples: Entamoeba, Acanthamoeba, Naegleria.
  • Movement: Extending projections of cytoplasm called pseudopods.
  • Entamoeba histolytica: The primary human intestinal pathogen, causing amoebic dysentery, which can be fatal.
  • E. histolytica consumes RBCs for nutrition (erythrophagocytosis).
  • Causes severe diarrhea.
  • Transmission: Ingestion of cysts from feces.
  • Important features of Entamoeba histolytica:
    • Cyst form
    • Trophozoite form

Facultative Protozoan Parasites

  • Naegleria fowleri
  • Acanthamoeba

Acanthamoeba

  • Habitat: water sources (tap and recreational), soil, sewage systems, cooling towers, and HVAC systems.
  • Infections: corneal infections (keratitis in contact lens wearers), lungs, disseminated infection.
  • Can invade the brain, causing fatal amoebic encephalitis.

Acanthamoeba keratitis

  • Advanced stage of Acanthamoeba keratitis.

Naegleria fowleri

  • Causes primary amebic meningoencephalitis (PAM), with a near 100% mortality rate.
  • Diagnosis usually occurs post-mortem due to rapid disease progression.
  • Free-living amoeba common in fresh water and soil.
  • Infection occurs when contaminated water is forced into the nose, typically during diving.
  • The amoeba travels to the brain, usually causing death within 10 days.