Parasitology: Acanthamoeba keratitis: 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 · Parasitology: Acanthamoeba keratitis

Sample item

A soft contact lens wearer who rinsed lenses with tap water has severe eye pain out of proportion to signs, with a ring-shaped corneal infiltrate. Bacterial cultures are negative. Which organism is most likely?

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

The answer and the reasoning

A. Acanthamoeba species

Acanthamoeba, a free-living amoeba found in tap water and soil, causes a painful sight-threatening keratitis in contact lens wearers, with radial perineuritis and a ring infiltrate. Corneal scrapings show double-walled cysts and trophozoites, and treatment uses topical biguanides such as polyhexanide (PHMB) or chlorhexidine.

Option by option

  • A. Acanthamoeba species (correct)

    Correct. Tap-water exposure with a ring infiltrate and negative cultures fits Acanthamoeba.

  • B. Toxoplasma gondii

    Toxoplasma gondii causes chorioretinitis rather than keratitis.

  • C. Naegleria fowleri

    Naegleria fowleri causes primary amoebic meningoencephalitis after nasal exposure to warm water.

  • D. Entamoeba histolytica

    Entamoeba histolytica causes intestinal and liver disease, not keratitis.

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 A, Acanthamoeba species. Acanthamoeba, a free-living amoeba found in tap water and soil, causes a painful sight-threatening keratitis in contact lens wearers, with radial perineuritis and a ring infiltrate.

Why is "Toxoplasma gondii" not the answer?

Toxoplasma gondii causes chorioretinitis rather than keratitis.

Why is "Naegleria fowleri" not the answer?

Naegleria fowleri causes primary amoebic meningoencephalitis after nasal exposure to warm water.

Why is "Entamoeba histolytica" not the answer?

Entamoeba histolytica causes intestinal and liver disease, not keratitis.

What concept does this question test?

It tests Parasitology: Acanthamoeba keratitis in Microbiology. Corneal scrapings show double-walled cysts and trophozoites, and treatment uses topical biguanides such as polyhexanide (PHMB) or chlorhexidine.

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 Parasitology: Acanthamoeba keratitis?

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.