RESUMO
Mice from the syngeneic strains BALB/c, C57B1/6 and (BALB/cxC57B1/6)F1 hybrids (CB6F1) were infected in the footpad with six different strains of Leishmania mexicana mexicana isolated from Mexican patients. Three Leishmania strains were isolated from patients with localized cutaneous leishmaniasis (LCL, the benign form of the disease) and three from patients with diffuse cutaneous leishmaniasis (DCL, the malignant form of the disease). In BALB/c mice, four Leishmania strains showed a sustained fast growth from 4 to 5 weeks postinfection until the end of the experiment (15 weeks), and the other two grew slowly up to 10 or 12 weeks after infection and then started to grow faster. In C57B1/6 mice four Leishmania strains showed a limited to moderate growth up to 6 to 11 weeks postinfection and then started to decrease. One strain showed a moderate growth during the entire experiment and one strain grew as fast as in BALB/c mice up to 11 weeks postinfection and then started to decrease. The CB6F1 hybrid behaved like the C57B1/6 parent strain with five Leishmania strains but was much more resistant to one Leishmania strain than the C57B1/6 mice. Sex of the mouse did not influence the outcome of infection. One important purpose of this work was to see if the Leishmania strains that cause DCL are intrinsically more virulent than those that cause the benign form (LCL). Although important variations in virulence among the Leishmania strains were observed, especially in BALB/c mice, they were not correlated with the type of disease caused in humans.
