Bacteriology: leprosy and lepromin test: 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.

Try it

Microbiology · Bacteriology: leprosy and lepromin test

Sample item

A 30-year-old man has a single hypoaesthetic, hypopigmented plaque with a raised, well-defined edge and a thickened adjacent nerve; slit-skin smear is negative. A lepromin test read at 21 days shows a strongly positive Mitsuda reaction. What does this indicate?

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

The answer and the reasoning

D. Good cell-mediated immunity, as in tuberculoid leprosy

The lepromin test is an intradermal skin test with heat-killed bacilli that measures delayed-type hypersensitivity; the late (Mitsuda) reaction is read at 3 to 4 weeks. It is positive in tuberculoid disease and negative in lepromatous disease, so it helps classification and prognosis but is not used for diagnosis because healthy exposed people also test positive.

Option by option

  • A. Recent exposure to Mycobacterium tuberculosis

    The Mitsuda reaction is specific to M. leprae antigen response, not a marker of M. tuberculosis exposure, and tuberculin testing is used for that.

  • B. Confirmation of the diagnosis of leprosy, irrespective of type

    Healthy contacts can also be lepromin-positive, so the test cannot confirm or exclude leprosy.

  • C. Lepromatous leprosy with poor cell-mediated immunity

    Lepromatous patients lack cell-mediated immunity to M. leprae and are lepromin-negative.

  • D. Good cell-mediated immunity, as in tuberculoid leprosy (correct)

    Correct. A strong Mitsuda reaction shows an effective cell-mediated response, typical of the tuberculoid pole.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Good cell-mediated immunity, as in tuberculoid leprosy. The lepromin test is an intradermal skin test with heat-killed bacilli that measures delayed-type hypersensitivity; the late (Mitsuda) reaction is read at 3 to 4 weeks.

Why is "Recent exposure to Mycobacterium tuberculosis" not the answer?

The Mitsuda reaction is specific to M. leprae antigen response, not a marker of M. tuberculosis exposure, and tuberculin testing is used for that.

Why is "Confirmation of the diagnosis of leprosy, irrespective of type" not the answer?

Healthy contacts can also be lepromin-positive, so the test cannot confirm or exclude leprosy.

Why is "Lepromatous leprosy with poor cell-mediated immunity" not the answer?

Lepromatous patients lack cell-mediated immunity to M. leprae and are lepromin-negative.

What concept does this question test?

It tests Bacteriology: leprosy and lepromin test in Microbiology. It is positive in tuberculoid disease and negative in lepromatous disease, so it helps classification and prognosis but is not used for diagnosis because healthy exposed people also test positive.

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: leprosy and lepromin test?

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.