Enteric Protozoa (GIT)

Question 1

What is the causative protozoa of amoebic dysentery?

Answer 1

Entamoeba histolytica.

Amoebic dysentery = inflammatory diarrhoea, stool has blood and pus (WBCs)

Question 2

Why is faecal morphology not a reliable way of diagnosing amoebic dysentery?

Answer 2

There are other Entamoeba species which also colonise the bowel, but are asymptomatic, making diagnosis unreliable.

Question 3

Describe the lifecycle + infection of humans of Entamoeba histolytica.

Answer 3

Entamoeba histolytica can exist in two forms:

1. Cyst (causes infection. survive in environment)
2. Trophozoite (motile invasive form)

Cysts are ingested in contaminated food + water.

In the bowel, cysts release trophozoites, which may invade bowel mucosa.

Trophozoites and cysts can be passed on in faeces.

Question 4

What are the clinical features of amoebic dysentery?

Answer 4

Diarrhoea with blood and pus in stool

Colitis

Ulceration of intestinal wall

Question 5

What is the pathogenic member of genus Giardia?

Answer 5

Giardia duodenalis

Question 6

What are the clinical manifestations of Giardia duodenalis infection?

Answer 6

50% have no symptoms and clear the infection.

35% are symptomatic, presenting with acute diarrhoea, abdo pain and nausea which can progress to chronic.

15% are asymptomatic cyst shedders/

Question 7

What is the pathogenesis of Giardia duodenalis?

What mechanisms contribute to causing diarrhoea?

Answer 7

Trophozoites adhere to intestinal epithelial cells, causing:

• Villous atrophy
• Disruption of epithelial junctions
• Apoptosis of epithelial cells
• Increased electrolyte levels in lumen

Diarrhoeal mechanisms:

• Less water reabsorption due to damage to epithelial cells
• Increased electrolytes in lumen pulls water in
• Waterl leaks through disrupted epithelial junctions