Leishmaniose visceral caninacorrelação da resposta imunológica com a carga parasitária e a variabilidade genética do parasita

Visceral leishmaniasis is a zoonotic disease in the New World and the domestic dog is the main host of Leishmania infantum . Prior knowledge of the immunopathogenic mechanisms associated with infection by L. infantum is required for the development of vaccines and other control strategies. The overall aim of this thesis was to compare the clinical expression, parasite load, the host immune response and genetic diversity of parasites in dogs naturally infected with L. infantum . This study is a cross - sect ional assessment of ninety - two dogs naturally infected by L. infantum . Infection was confirmed by serology, parasite culture and / or PCR. The etiology was assessed by hsp70 PCR - RFLP and MLEE . We further analyzed clinical signs , immune response by cytokine gene expression, molecular parasite load by qPCR, histological changes in sple nic and hepatic compartments and also L. infantum populations and genotypes through microsatellite analysis. Groups according to the spleen and liver parasite load were defined. Animals with high parasite load had high titers of anti - Leishmania antibodies and more clinical signs. The paras ite load in the spleen was higher than in liver and correlated with disruption of splenic architecture, mainly characterized by white pulp diso rganization. Liver parasite load was correlated with the occurrence of granulomas, degeneration and intensity of the inflammatory infiltrate. We show that the higher parasite load promoted lower gene expression o f IL - 12, IFNγ, TNF, IL - 6, IL - 10 and TGFβ in the spleen and increased expression of CCL2, CXCL8 MAP4K4 in the liver. Genetic analysis of parasites is indicative of polyclonal infection and tissue tropism of some clones, more evident in the analysis of paire d samples ( strain isolated and tissue). We also found l ow genetic variability , in which the majority (96%, 49/51) of the samples was characterized as belonging to POP2, among tree populations previously described by our group. There was no association betw een the genetic variability of the parasites and the clinical, parasitological and immunological parameters. Nevertheless, the data generated by in vitro assays with strains from different populations suggest that there are differences in infectivity betwe en strains with distinct m icrosatellite genotypes. Taken together, these results show that in the region studied Canine Leishmaniasis is caused by genetically homogeneous population without any correlation between specific genotypes and the phenotype of ca nine infection .