Authors

Discussion

Genetic variability of Trypanosomatids may impact the outcome of infection, drug resistance or epidemiological traits of diseases. Discrepant geographic distribution of a deletion (DEL) in the Mitelfosine Sensitivity Locus (MSL) on chromosome 31 of Leishmania infantum was described in Brazil: Del strain (DEL) was identified in 15 Brazilian states whereas the non-deleted (Non-DEL) in 7. We hypothesized then that a subclinical and less detectable infection caused by DEL in the canine reservoir might persist for long-term in endemic areas, contributing to the greater spread of DEL than Non-DEL strain. To test the hypothesis, we performed a genome-wide association study (GWAS) to better understand the impact of the MSL on the clinical-immunological outcome in dogs naturally infected by L. infantum. From a set of 234 dogs, clinical outcome, parasite load, humoral immunity were evaluated, as well as the genomic DNA was genotyped by SNPchip Canine HD (Illumina) with 118,786 reliable SNPs. For the subset of 60 dogs, the MSL was genotyped by qPCR on lymph node aspirates (33 DEL/27 Non-DEL infections) in order to investigate if clinical-immunological traits of subclinical infection were associated to DEL infection; the presence of dog genetic background (DGB) associated with predominant adaptation of DEL or Non-DEL; and if the inclusion of MSL as covariate change the significance of SNPs associated to clinical-immunological traits. When we regressed clinical-immunological traits onto environmental covariates (origin, sex, age, repellent collar, anti-Leishmania vaccine or treatment) and MSL genotypes, only anti-L. infantum IgA had a significant association (p = 0.00554) with MSL whereas clinical staging was only suggestively associated (p = 0.09639). Both lower clinical severity and low IgA levels were associated with DEL infection. Infection made by the DEL strain was also more frequent in dogs carrying an allele associated with low levels of anti-L. infantum IgG (P < 0,0001), confirming the hypothesis of mild infection caused by DEL strain. No principal component analysis (PCA) cluster, estimated heritability (REML) or SNP significantly associated with MSL were identified in dog genome indicating absence of direct association between the DGB and MSL. On the other hand, the inclusion of MSL as covariate slightly increased the significance of SNPs associated with anti-L. infantum IgG and IgM. These data strongly suggest that although there is no dog genotype directly associated to predominant adaptation of DEL or Non-DEL strains during the L. infantum infection, distinct MSL genotypes may differently interact with the host's immune system of dogs, leading to different clinical-immunological outcomes and effect of their genetic basis, potentially impacting the epidemiology of the canine visceral leishmaniasis.