What is the infection chain of Paragonimiasis?

Appeared in: DSSSB October 2024

Explanation

Paragonimiasis is caused by the lung fluke Paragonimus westermani.
The life cycle requires two intermediate hosts before infecting the definitive host (humans).
The first intermediate host is a freshwater snail, and the second is a freshwater crustacean (crab or crayfish).
Humans become infected by consuming raw or undercooked crabs or crayfish containing the parasite's metacercariae.
This makes the correct infection chain Man-Snail-Crab-Man.

Option A: This chain lacks a second intermediate host. The parasite does not go directly from a snail back to a human.
Option B: The second intermediate host for Paragonimiasis is a crab or crayfish, not a fish.
Option C: The first intermediate host for Paragonimiasis is a snail, not a Cyclops (a type of copepod).

Clinical Relevance

Nursing practice connection: Knowing Life cycle of Paragonimus westermani helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
A key nursing intervention is obtaining a thorough dietary history from patients presenting with chronic cough and hemoptysis, especially if they have lived in or traveled to endemic areas.
Paragonimiasis is often misdiagnosed as tuberculosis due to similar respiratory symptoms. A negative TB test in a patient with these symptoms and a relevant dietary history should raise suspicion for paragonimiasis.
Patient education is crucial for prevention. Nurses should advise patients and communities in endemic areas about the dangers of eating raw or undercooked freshwater crabs and crayfish and teach proper cooking methods.

How to Approach the Question

First, identify the key term in the question: 'Paragonimiasis'. This is a direct recall question about the life cycle of a specific parasite.
Recall or deduce the type of organism. The '-iasis' suffix suggests a parasitic infection. 'Paragonimus' is a genus of trematode (fluke).
Think about the general life cycles of trematodes. Many require one or two intermediate hosts, which are often mollusks (snails) and then another aquatic organism (fish, crustacean, or plant).
Evaluate each option based on this knowledge:
'Man-Snail-Man' implies direct transmission from snail to human, which is typical for Schistosoma.
'Man-Snail-Fish-Man' is a common pattern for liver flukes like Clonorchis.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 1 pp. 1872-1874, 1873-1875

E6 Medicine Davidson Principles Practice 24e p. 317-319

Practise the full DSSSB October 2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.