Micro W2: Intestinal Protozoa

What are intestinal protozoa?

Single-celled eukaryotic parasites that infect the human gastrointestinal tract and are commonly identified in stool specimens.

How are intestinal protozoa primarily classified?

By their mode of motility: amoebae (pseudopodia), flagellates (flagella), ciliates (cilia), and sporozoa (no motility organelles).

What is a trophozoite?

The active, motile, feeding stage of a protozoan that causes disease in the host.

What is a cyst?

The dormant, environmentally resistant stage responsible for transmission and survival outside the host.

Which protozoan stage is usually infectious to humans?

The cyst (or oocyst in sporozoa)

What structure allows amoebae to move and feed?

Pseudopodia (temporary extensions of cytoplasm).

What nuclear features are key for identifying amoebae?

Karyosome position and peripheral chromatin pattern.

What is a karyosome?

A dense DNA structure within the nucleus used for species identification.

What are chromatoid bodies?

Aggregates of ribosomal RNA seen in cysts; shape and size help with species identification.

Which amoeba is pathogenic?

Entamoeba histolytica.

How does Entamoeba histolytica cause disease?

By invading intestinal tissue, causing flask-shaped ulcers and possible extraintestinal spread.

What key microscopic feature distinguishes Entamoeba histolytica?

Trophozoites containing ingested red blood cells.

Which Entamoeba species are nonpathogenic?

Entamoeba dispar, Entamoeba coli, Entamoeba hartmanni, Endolimax nana, Iodamoeba butschlii.

What is the primary transmission route for intestinal protozoa?

Fecal-oral ingestion of cysts or oocysts.

What defines flagellates?

Protozoa that move using one or more flagella.

Which flagellate is the most common intestinal pathogen?

Giardia duodenalis.

What are key identifying features of Giardia duodenalis?

Two nuclei (face-like appearance), ventral sucking disk, falling-leaf motility.

What disease does Giardia cause?

Giardiasis characterized by greasy, foul-smelling diarrhea and malabsorption.

What is the ventral disk?

An attachment organelle in Giardia that allows adherence to the intestinal mucosa.

Which protozoan is the only ciliate infecting humans?

Neobalantidium coli.

What unique nuclear feature identifies ciliates?

Presence of both a macronucleus and micronucleus.

What is the primary reservoir for Neobalantidium coli?

Pigs

What defines sporozoa (Apicomplexa)

Protozoa with complex life cycles, no motility organelles, and an apical complex.

What is an apical complex?

A specialized structure used by sporozoa to invade host cells.

Which sporozoan causes severe diarrhea in immunocompromised patients?

Cryptosporidium spp.

How is Cryptosporidium identified in stool?

Modified acid-fast stain showing small acid-fast oocysts.

Why is Cryptosporidium clinically significant?

It is resistant to chlorine and causes life-threatening diarrhea in AIDS patients.

How does Cyclospora differ from Cryptosporidium?

Cyclospora has larger, variably acid-fast oocysts and causes prolonged diarrhea.

What is Blastocystis spp.?

A common intestinal protozoan with controversial pathogenicity, identified by a large central vacuole.

What diagnostic methods are commonly used for intestinal protozoa?

Ova and parasite exam, trichrome stain, acid-fast stain, antigen tests, and PCR.