In lepromatous leprosy, bacilli preferentially accumulate in the skin, earlobes, nasal mucosa, anterior segment of the eye, and testes rather than in deep viscera. What property of M. leprae accounts for this tissue tropism?
- A Optimal growth at cooler temperatures around 30 to 33 degrees C ✓
- B Binding of bacilli exclusively to keratinocytes
- C Requirement for high oxygen tension found only in skin capillaries
- D Selective susceptibility of stratified squamous epithelium to lepra toxins
Correct answer: A. Optimal growth at cooler temperatures around 30 to 33 degrees C
Explanation
M. leprae grows optimally below core body temperature, around 30 to 33 degrees C, so it thrives in cooler superficial sites: skin, peripheral nerves, nasal mucosa, earlobes, eyes, and testes. This explains the facial infiltration, testicular atrophy causing infertility, and corneal involvement seen in lepromatous disease while deep warm organs are spared. Option B is incorrect because the key host cells are Schwann cells and macrophages, not keratinocytes.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.