The susceptibility of 12 strains of inbred mice representing a broad genetic spectrum to infection of Leishmania braziliensis, L. mexicana and L. aethiopica was determined. Levels of susceptibility were evaluated by gross morphology of lesions, evidence of resolution, persistence of parasites at the site of inoculation, and visceralization to the spleen or liver following inoculation in noses. Very different patterns of responses were noted among the infections with the three species of Leishmania.

Among the strains of inbred mice infected with L. braziliensis, patterns of cutaneous lesion development indicated a broad range of susceptibilities and responses. Two strains of inbred mice (AKR/J and CBA/J) showed only a slight and transient swelling of the nose. The SWR/J, C57L/J, A/J, A/HeJ and DBA/IJ showed initial swellings or nodules which eventually resolved. In contrast, the BALB/cJ mice were ranked as most susceptible, based on progressive dermal lesions and visceralization. Four strains of inbred mice (C3H/HeJ, C57BL/6J, CBA/J and CBA/CaJ) showed no evidence of infection.

Lesion development in most strains of inbred mice infected with L. mexicana occurred later than with L. braziliensis but was then more rapidly progressive with no indication of resolution. Two strains (C3H/HeJ and C57BL/6J) showed no evidence of infection.

Only slight swellings of the nose were seen in the 12 strains of inbred mice infected with L. aethiopica; however, parasites were isolated by culture from apparently normal noses in five groups (A/HeJ, AKR/J, BALB/cJ, DBA/2J and SWR/J).