Infectivity of leprosy bacilli from bone marrow and liver of patients with lepromatous leprosy.

Specimens of b one m arrow or liver were coHected from patien ts with lepromatous leprosy at the same time that skin biopsy specimens were removed . The viability of the bacilli was measured by inoculation into mice. There were 2 0 bone ·marrow specimens, and infectivity for mice was present in all of the 1 6 that came from patients whose skin specim ens contained bacill i infective for mice. The incubation period was shorter with skin specimens in 1 0 cases. I t did not differ by m ore than 2 m onths except in 3 cases, and in all 3 it was shorter with skin specimens. Thus, although viable Myco. leprae were present in marrow, the evidence suggests that in m ost instances the proportion of viable bacilli was somewhat less than in skin . Five liver specimens were studied similarly . The bacillary viability in these specimens appeared also to be somewhat less than in the skin specimens. These results are consistent with the hypothesis that the primary site of bacillary multiplication in lepromatous leprosy is in the skin and nasal mucosa, and that the bacilli enter the bloodstream from these sites, to be removed by phagocytes of the bone m arrow and liver and other members of the reticulo-endothelial system.