Communicable diseases: hydatid disease epidemiology: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Communicable diseases: hydatid disease epidemiology

Sample item

A child from a sheep-rearing family has a slowly enlarging cystic swelling in the liver. The family keeps working dogs that are fed raw offal. In the epidemiology of this infection, what is the role of the child?

ADefinitive host harbouring adult wormsBBiological vector carrying infective larvaeCAccidental intermediate host, a dead end for the parasiteDReservoir host maintaining the cycle

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Accidental intermediate host, a dead end for the parasite

In Echinococcus granulosus infection, dogs are the definitive hosts carrying adult worms and sheep are the usual intermediate hosts. Humans become infected by swallowing eggs from dog faeces and act as accidental intermediate hosts, so the cycle ends with them.

Option by option

A. Definitive host harbouring adult worms
The definitive host is the dog, which carries the adult tapeworm in its intestine.
B. Biological vector carrying infective larvae
A vector is an arthropod that transmits infection, and humans do not transmit this parasite.
C. Accidental intermediate host, a dead end for the parasite (correct)
Correct. Humans harbour the cyst stage only and do not pass the infection on, so they are a dead end.
D. Reservoir host maintaining the cycle
Sheep and dogs maintain the cycle, and a person with a cyst does not.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Accidental intermediate host, a dead end for the parasite. In Echinococcus granulosus infection, dogs are the definitive hosts carrying adult worms and sheep are the usual intermediate hosts.

Why is "Definitive host harbouring adult worms" not the answer?

The definitive host is the dog, which carries the adult tapeworm in its intestine.

Why is "Biological vector carrying infective larvae" not the answer?

A vector is an arthropod that transmits infection, and humans do not transmit this parasite.

Why is "Reservoir host maintaining the cycle" not the answer?

Sheep and dogs maintain the cycle, and a person with a cyst does not.

What concept does this question test?

It tests Communicable diseases: hydatid disease epidemiology in PSM. Humans become infected by swallowing eggs from dog faeces and act as accidental intermediate hosts, so the cycle ends with them.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Communicable diseases: hydatid disease epidemiology?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.