Intestinal Protozoan Infections

Key Protozoans

• Entamoeba histolytica
• Giardia lamblia
• Opportunistic coccidian parasites

Structure

• Part 1: Introduction to protozoans
• Part 2: Lifecycle of these protozoans
• Part 3: Lab diagnosis of protozoans

Entamoeba Histolytica

• Belongs to intestinal amoeba group.
• Only pathogenic amoeba in this group.
• Causes amoebic dysentery (diarrhea + blood).
• Stages in life cycle:
  • Trophozoite: invasive form
  • Precyst: intermediate stage
  • Cyst: diagnostic form
• Differences with Entamoeba coli:
  • E. histolytica causes infection, E. coli does not.
  • Size, cytoplasm, inclusions differ between trophozoites.

Giardia Lamblia

• Causes giardiasis (watery diarrhea).
• Does not cause dysentery (no blood).
• Only flagellated intestinal protozoan.
• Exists in two forms:
  • Trophozoite: invasive stage
  • Tetra-nuclear cyst: infective and diagnostic form

Opportunistic Coccidian Parasites

• Includes Cryptosporidium, Cyclospora cayetanensis, Cystoispora belli.
• Cryptosporidium:
  • Auto-infection observed.
  • Oocyst in feces is sporulated.
  • Sporulation occurs in the intestine.

Key Differences in Parasites

• Cryptosporidium:
  • Auto-infection.
  • Sporulated oocysts in feces.
  • Intestinal sporulation.
• Cyclospora & Cystoispora:
  • Oocysts in feces are not sporulated.

Diagnostic Tools

• PCR: Differentiate between E. histolytica and non-pathogenic amoebas.
• Oocyst Identification: Critical for diagnosing cryptosporidium infections.

Important Notes

• E. histolytica trophozoite is invasive; cyst is diagnostic.
• Giardia cyst is both infective and diagnostic.
• Cryptosporidium is differentiated by auto-infection and sporulated oocysts.

Examination Tips

• Diagrams of trophozoites and cysts aid memory.
• Clearly differentiate between amoebic and bacterial E. coli.
• Prepare for differences in university exams and viva.

This chapter lays the foundation for understanding the life cycle and diagnosis of intestinal protozoan infections which will be covered in subsequent parts.