Introduction to parasitology

Question 1

What are the sources and routes of parasitic infection in humans. (5)

Answer 1

• Animals
• Blood
• Food
• Insects
• Water

Question 2

What is the nematode life cycle (6)

Answer 2

1. adult roundworms lay eggs in host GI tract
2. eggs pass in host faecal matter
3. eggs hatch into 1st stage larvae in dung pat
4. 1st stage larvae develop into 2nd stage in manure
5. 2nd stage develops into 3rd stage in manure and migrate to vegetation
6. larvae ingested by the host migrate to the GI tract and develop into adults

Question 3

What is the Taenia solium life cycle (6)

Answer 3

1. humans eat raw or undercooked cysticerci in muscle
2. parasites grow to its adult form in the small intestine
3. eggs are deposited in the large intestine and released to the environment
4. cattle and pigs become infected by ingesting contaminated vegetation
5. oncospheres penetrate the intestine wall and travel to the musculature
6. oncospheres develop into cysticerci in muscle

Question 4

What is lice life cycle (6)

Answer 4

1. egg
2. 1st nymph
3. 2nd nymph
4. 3rd nymph
5. 4th nymph
6. 5th nymph

Question 5

What is the Cryptosporidium spp. life cycle (6)

Answer 5

1. Humans ingest thick-walled oocysts in contaminated water
2. parasites reproduce in the small intestine
3. thick-walled oocysts (sporulated) are released into the environment
4. water and food from human-populated areas get contaminated with oocysts

Question 6

What is the Schistosoma mansoni life cycle (8)

Answer 6

1. cercariae penetrates skin
2. cercariae become schistosomulae
3. migration to a portal vein in the liver and maturation into adults
4. paired adult worms migrate to the bowel/rectum. It lays eggs and sheds in stool
5. eggs hatch and release miracidia
6. miracidia penetrate snail tissue
7. sporocytes successive generations
8. free-swimming cercaria released into the water

Question 7

What is the Malaria life cycle (4)

Answer 7

1. Infected mosquitos release sporozoites into humans
2. sporozoites become merozoites in liver cells
3. merozoites are released into the blood where they undergo asexual reproduction in red blood cells
4. Trophozoites → schizont → gametocytes which are transmitted back to mosquitoes