MCQ of the Day: 4 November 2026

Anaesthetic hypopigmented patches with peripheral nerve thickening and acid-fast bacilli in slit-skin smears point to leprosy, caused by Mycobacterium leprae; India reports more new cases than any other country. M. leprae is an obligate intracellular organism that cannot be cultivated in vitro. Shepard (1960) showed limited, reproducible multiplication after inoculation into the footpads of mice, and this model remains the classic method for assessing viability and drug resistance, with a long generation time of about 12 to 14 days. The nine-banded armadillo supports disseminated infection and is used to obtain large numbers of bacilli.
A (Rabbit testis): used to propagate Treponema pallidum (Nichols strain), which also cannot be grown on artificial media.
C (Guinea pig peritoneum): intraperitoneal inoculation of male guinea pigs gives the Neill-Mooser reaction with Rickettsia typhi and the Strauss reaction with Burkholderia mallei; guinea pigs are also the classic animal for M. tuberculosis virulence, not M. leprae.
D (Embryonated egg yolk sac): used for rickettsiae and Chlamydia.