In vitro Infectivity of Strains Isolated From Dogs Naturally Infected With Leishmania infantum Present a Distinct Pathogenic Profile in Hamsters.

Visceral leishmaniasis (VL) is a severe disease caused byLeishmania infantum. Dogs are the parasite's main reservoir, favoring its transmission in the urban environment. The analysis ofL. infantumfrom infected dogs contributes to the identification of more virulent parasites, thereby supporting basic and applied studies such as vaccinal and therapeutic strategies. We proposed thein vitroandin vivocharacterization ofL. infantumstrains from naturally infected dogs from a VL endemic area based on an infectivity and pathogenicity analysis. DH82 canine macrophages were infectedin vitrowith different strains for infectivity analysis, showing distinct infectivity profiles. The strains that showed greater and lesser infectivity usingin vitroanalyses (616 and 614, respectively) were used to infect hamsters for pathogenicity analysis. The group infected with strain 616 showed 100% survival while the group infected with strain 614 showed 50% after seven months of follow up. Furthermore, the 614 strain induced more noticeable clinicopathological changes and biochemical abnormalities in liver function, along with high inflammation and parasite load in the liver and spleen. We confirmed high variability of infectivity and pathogenicity inL. infantumstrains from infected dogs. The results support the belief that screening forL. infantuminfectivity usingin vitroexperiments is inadequate when it comes to selecting the most pathogenic strain.