Helminths

Question 1

If you identified larvae in a stool specimen, would they be rhabditiform larvae or filariform larvae?

Answer 1

Rhabditiform larvae

Question 2

How could you distinguish between the rhabditiform larvae of a hookworm (rare in faeces but possible) and Strongyloides stercoralis?*

Answer 2

size? head/scolex?
- Rhabiditiform: 300um
- Filariform: 600um

Question 3

Which parasite is also known as the cucumber tapeworm?

Answer 3

Dipylidium caninum

Question 4

Which parasite is also known as the oriental lung fluke?

Answer 4

Paragonimus westermani

Question 5

If you identified a parasite in a faecal wet mount that had an operculum, what would be the first step in
determining which species it belonged to?

Answer 5

Consider the size:
30um: Clonorchis sinensis
65um: Diphyllobothrium latum
85um: Paragonimus westermani
140um: Fasciola buski
145um: Fasciola hepatica

Question 6

Which helminth is acquired by the ingestion of a larvae rather than an an egg?

Answer 6

Trichostrongylus (filariform larvae)

Question 7

Which cestode can grow at 22cm per day and release up to 1,000,000 eggs per day?

Answer 7

Diphyllobothrium latum

Question 8

How are infections contracted by humans:
a) Diphyllobothrium latum,
b) Paragonimus westermani and
c) Dipylidium caninum

Answer 8

a) ingest pleroceroid larvae in uncooked fish
b) ingest uncooked crustasean w/ metacercariae
c) Swallowing infected fleas (cysticeroid)

Question 9

If a pet dog or cat was seen dragging its rear end across the ground, which parasite could be indicated?

Answer 9

Dipylidium caninum

Question 10

lifecycle of Diphyllobothrium latum (7)

Answer 10

1. Unembryonated eggs in human faeces (Dx)
2. Eggs embryonate in water
3. Corcacidia hatch from eggs & ingested by crustaceans
4. develop into preocercoid in crustacean
5. ingested by a small fish & develop into plerocercoid
6. Big fish eats small fish
7. Human ingest big fish & parasite develop into adulthood in human

Question 11

lifecycle of Dipylidium caninum

Answer 11

1. cucmber proglottid in dog/cat/human poo (dx)
2. embryonated eggs in packets ingested by flea
3. develop into oncosphere => cysticercoid (infective)
4. flea gets ingested by cat/dog/child
5. adult tapeworm develop

Question 12

Lifecycle of Paragonimus westermani

Answer 12

1. Unembryonated egg (dx) in human poo or spit
2. becomes embryonated in environment
3. Miracidia hatch & penetrate snail
4. Sporocyst -> Rediae -> Cerariae -> metacariae (infective)
5. metcariae swims & infects crustacean
6. Human eat raw/undercooked crustasian