Leprosy is caused by:

Concept

An etiological question asks which pathogen causes a disease. The reliable method is to match the disease with its established pathogen at genus and species level.

The organism’s defining microbiological features can then be used as a cross-check, while the remaining genera are contrasted with their characteristic diseases.

Application

Leprosy (Hansen’s disease) is caused by Mycobacterium leprae. It is an acid-fast, slow-growing, rod-shaped bacterium with a lipid-rich cell wall containing mycolic acids; the disease chiefly affects the skin, peripheral nerves, and mucous membranes. Therefore the matching offered genus is Mycobacterium.

Contrast

• Haemophilus includes Gram-negative coccobacilli associated with illnesses such as invasive meningitis and epiglottitis.

• Clostridium includes anaerobic, spore-forming rods associated with illnesses such as tetanus and botulism.

• Corynebacterium includes Gram-positive, club-shaped rods; Corynebacterium diphtheriae causes diphtheria.

Cross-check

The accepted species name contains the genus Mycobacterium, and none of the other offered genera contains the leprosy-causing species.

Result

The answer is Mycobacterium.