Bacteriology: scrub typhus: practice question

A Microbiology 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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Microbiology · Bacteriology: scrub typhus

Sample item

A farmer who cleared bushland two weeks ago has high fever, headache and lymphadenopathy. There is a painless black eschar in the axilla. The Weil-Felix test is performed. Which result is expected, and what is the vector?

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

The answer and the reasoning

C. Agglutination of Proteus OX-K, with trombiculid mite larvae as the vector

Scrub typhus is caused by Orientia tsutsugamushi and is spread by the larvae (chiggers) of trombiculid mites. It is the rickettsial disease for which OX-K agglutination is positive in the Weil-Felix test, though the test is insensitive. Doxycycline is the treatment of choice.

Option by option

  • A. Agglutination of Proteus OX-K, with rat fleas as the vector

    Rat fleas transmit murine typhus, which gives OX-19 and not OX-K.

  • B. Agglutination of Proteus OX-2 mainly, with ixodid ticks as the vector

    OX-2 and ticks fit the spotted fever group, which is not suggested by this exposure and eschar location.

  • C. Agglutination of Proteus OX-K, with trombiculid mite larvae as the vector (correct)

    OX-K agglutination with chigger vector matches scrub typhus with an eschar.

  • D. Agglutination of Proteus OX-19 strongly, with human body lice as the vector

    OX-19 with body lice describes epidemic typhus due to Rickettsia prowazekii.

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.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Agglutination of Proteus OX-K, with trombiculid mite larvae as the vector. Scrub typhus is caused by Orientia tsutsugamushi and is spread by the larvae (chiggers) of trombiculid mites.

Why is "Agglutination of Proteus OX-K, with rat fleas as the vector" not the answer?

Rat fleas transmit murine typhus, which gives OX-19 and not OX-K.

Why is "Agglutination of Proteus OX-2 mainly, with ixodid ticks as the vector" not the answer?

OX-2 and ticks fit the spotted fever group, which is not suggested by this exposure and eschar location.

Why is "Agglutination of Proteus OX-19 strongly, with human body lice as the…" not the answer?

OX-19 with body lice describes epidemic typhus due to Rickettsia prowazekii.

What concept does this question test?

It tests Bacteriology: scrub typhus in Microbiology. It is the rickettsial disease for which OX-K agglutination is positive in the Weil-Felix test, though the test is insensitive. Doxycycline is the treatment of choice.

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 Bacteriology: scrub typhus?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.