Authors

Discussion

The domestic dog (Canis lupus familiaris) is the main reservoir of the visceral leishmaniasis (VL) in urban environment and a model for study of VL. Explore the genetic basis of the Leishmania infantum natural infection in domestic dogs can increase the understanding of the balance of different factors that lead to different clinical-immunological outcomes in visceral leishmaniasis. Here, we examine a set of 234 dogs from Brazil to investigate how much impact the dog genetic background (DGB) has on canine VL (CVL), employing heritability analysis (HA) and genome-wide association study (GWAS). Before the genotype-phenotype association analysis, the genomic DNA from blood samples was genotyped by SNPchip Canine HD (Illumina) with 118,786 reliable SNPs upon filtration. Also, CVL phenotypic traits related to clinical outcome, parasite load, humoral immunity, cell-mediated immunity, and oxidative stress were adjusted with L. infantum Mitelfosine Sensitivity Loci (MSL) and epidemiological covariates that may impact exposure to the parasite or the responsiveness to infection (geographic origin, sex, age, repellent collar, anti-visceral leishmaniasis vaccine and treatment) in order to select the best model increasing the accuracy on HA and GWAS. Among the models, the combination of all epidemiological covariates was what most brought the traits closer to the Gaussian distribution, improved the Q-Q plots, increased the accuracy on the HA, and reduced spurious associations on GWAS, except for the traits anti-L. infantum IgA, anti-salivary gland lysate (SGL) of Lutzomyia longipalpis IgG, leishmanin skin test [LST], IL-10, IFN-g, TNF-a, NO. Inclusion of MSL as covariate in the HA did not significantly change the proportion of clinical-immunological outcomes explained by the DGB. The effect of the DGB was predominant when we compared with the MSL and epidemiological covariates effects, mainly for the traits anti-L. infantum IgG (~90% heritability), clinical staging (~40%), and total antioxidant capacity [TAC] (~42%), indicating that many dog genetic signatures contribute to these traits. Candidate genes for anti-L. infantum IgG-SNPs are involved in TLR4 inhibition (PTPN4) and cytokine receptors (IL2R and IL15R). IL6 is one of the candidate genes for clinical staging and NOS1 candidate gene for TAC. The effect of the DGB was lower but still predominant for PBMC proliferation index [PI] (~28%), superoxide dismutase [SOD] (25%), IgE (~25%), IgM (~24%), clinical outcome (~18%), TGF-b (~17%), total oxidant capacity [TOC] (~15%). For those traits, only for 2 SNPs associated to IgM the significance was above the GWAS cut off. For both, the candidate genes are related to innate immune response (IL17C and MD2 - also involved in TLR4 signalling). Altogether, our findings point to the predominance of the host genome effect on the cli