Parasitology Exam 3 (Protozoa)

How are the 4 main groups of protozoa classified?

By how they move: amoebas (pseudopods), flagellates (whips), ciliates (hairs), and apicomplexa (don't move).

Cyst vs. Trophozoite: Which is the infective stage, and what does each do?

• Cyst = The Armor (dormant, tough, survives environment). This is the infective stage

• Trophozoite = The Soldier (active, motile, feeding, tissue-destroying). Fragile; destroyed by stomach acid if swallowed bare.

What is the ONLY pathogenic intestinal amoeba?

Entamoeba histolytica

How do you tell E. histolytica apart from the identical, harmless E. dispar under a microscope?

Only E. histolytica will be actively ingesting Red Blood Cells (RBCs).

What shape is the intestinal lesion caused by E. histolytica?

A flask-shaped lesion (ulcer with a narrow neck and a wide, hollowed-out base).

Where does E. histolytica metastasize after breaking through the intestinal wall?

It rides the bloodstream to the liver and lungs, causing massive abscesses.

What is the medical significance of finding non-pathogenic (commensal) amoebas in stool?

They are "Poop Indicators". Because their cysts survive putrefaction, their presence is absolute proof the patient swallowed fecal matter (sanitation failure).

Naegleria fowleri: Environment, Entry rule, and Disease?

• Warm fresh water

• Entry: MUST be forcefully shoved up the nose (Neti pot / jumping in lakes)

• Drinking it does not infect you

• Disease: PAM (rapid brain destruction, death in < 10 days).

How does Naegleria fowleri physically enter the brain from the nose?

1. Nose: Water containing the amoeba enters deep into the nasal cavity.

2. Nasal Mucosa: The amoeba attaches to the wet lining of the upper nose.

3. Cribriform Plate: It crawls through the tiny holes of this sieve-like bone at the roof of the nose.

4. Olfactory Nerves: It hitches a ride along the smell nerves that pass through those holes.

5. Meninges & Brain: It enters the brain's protective layers (meninges) and directly attacks the brain tissue.

Acanthamoeba: Environment and Brain Disease?

• Lives anywhere (soil, dust, water)

• Enters via broken skin or inhaled dust

• Disease: GAE (slow, creeping brain infection that takes weeks)

• Targets the immunocompromised.

What non-brain disease does Acanthamoeba cause, and who is the classic patient?

• Keratitis (blinding corneal infection)

• Classic patient: Contact lens users who wash their lenses in tap water instead of sterile saline.