Molecular epidemiology and in vitro evidence suggest that Leishmania braziliensis strain helps determine antimony response among American tegumenary leishmaniasis patients.

Antimony is the first line drug for treating American tegumentary leishmaniasis (ATL) in Brazil. In this country, Leishmania braziliensis causes at least three distinct forms of disease: localized cutaneous (CL), mucosal (ML) and disseminated leishmaniasis (DL). All forms can be found in Corte de Pedra, Northeast Brazil. ML and DL respond poorly to antimony, in contrast to CL. The L. braziliensis population causing ATL in Corte de Pedra is genetically very diverse, with strains of the parasite associating with the clinical form of leishmaniasis. We tested the hypotheses that antimony refractoriness is associated with L. braziliensis genotypes, and that parasites from ML and DL present greater in vitro resistance to antimony than L. braziliensis from CL. Comparison of geographic coordinates of living sites between antimony responders and non-responders by Cusick and Edward́s test showed that refractoriness and responsiveness to the drug were similarly wide spread in the region (p>0.05). Parasites were then genotyped by sequencing a locus starting at position 425,451 on chromosome 28, which is polymorphic among L. braziliensis of Corte de Pedra. Haplotype CC- in CHR28/425,451 was associated with risk of treatment failure among CL patients (Fisheŕs exact test, p=0.03, odds ratio=4.65). This haplotype could not be found among parasites from ML or DL. Finally, sensitivity to antimony was evaluated exposing L. braziliensis promastigotes to increasing concentrations of meglumine antimoniate in vitro. Parasites from ML and DL were more resistant to antimony at doses of 2mg/100μL and beyond than those isolated from CL (Fisher's exact test, p=0.02 and p=0.004, respectively). The intrinsically lower susceptibility of L. brazliensis from ML and DL to antimony parallels what is observed for patients' responsiveness in the field. This finding reinforces that ML and DL patients would benefit from initiating treatment with drugs currently considered as second line, like amphotericin B.