Parasitic infections of GI tract

Question 1

Pathogenesis and life cycle of intestinal parasitic protozoa

Answer 1

• Examples of GI parasitic protozoa: amoeba, flagellate, coccidia
• Dx: look for the cysts in solid stool, trophozoites in liquid stool (if its worms then look for eggs)
• Transmission: fecal-oral via ingestion of contaminated food, water
• Life cycle: ingestion of cysts, which mature into trophozoites (stay in bowel)
• Trophozoites multiply via binary fission, form cysts and are excreted in stool as cysts
• Can cause diarrhea, amoebas can cause liver abscesses

Question 2

Pathogenesis and life cycle of tapeworms 1

Answer 2

• Taenia saginata (cow) and T solium (pork) tapeworms are common, sodium being more dangerous
• Life cycle: proglottids (segments) break off the worm and are carried out into soil via stool
• Proglottids are eaten by cow/pig and the proglottids release 50-100k eggs in the stomach of the animal which mature into larva

Question 3

Pathogenesis and life cycle of tapeworms 2

Answer 3

• The large penetrate the gut, enter circulation, and eventually reach muscle
• If a human eats raw or under cooked meat the larva will mature into an adult worm and the cycle starts over
• Cysticercosis: due to human ingestion of eggs, rather than larva (T solium, pork worm, only)
• The eggs hatch into larva in human stomach, penetrate GI wall into blood stream and then invade tissues (most important is CNS, but also eyes, heart)

Question 4

4 species of GI parasitic roundworms

Answer 4

• Enterobius vermicularis (aka pinworm), use scotch tape test at anus to catch the worms as they migrate there in the morning
• Ascaris lumbricoides (aka roundworm)
• Necator americanus (a hookworm
• Ancylostoma duodenale (a hookworm)

Question 5

Dx for GI parasitic infections

Answer 5

• Scotch tape test for pinworm (enterobius vermicularis)
• If they are worms then look for the eggs/proglottids in stool
• If they are protozoa then look for the cysts (in solid stool) or trophozoites (in liquid stool)