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Abstract: Visceral leishmaniasis (VL) is a life-threatening disease of medical, social and economic importance in endemic areas. Dogs are the main reservoir of Leishmania infantum. In this study, the authors investigated a group of 56 natural infected dogs to establish the relationship between parasite load and various clinical forms of leishmaniasis. The sick dogs were monitored at the beginning from clinical and physiological point of view. Leishmania load was measured by real-time PCR assay on whole blood samples and lymph node aspirates, collected at the time of diagnosis. Our results indicate that a higher quantity of Leishmania DNA was found in the lymph nodes of dogs characterized by maximum clinical score. This interesting finding indicates the presence of a positive relationship between Leishmania load and clinical manifestations in dogs showing a severe clinical form of leishmaniasis. [Copyright &y& Elsevier]

[Display omitted] • Feline Leishmania strains are phenotypically similar to those from humans and dogs. • Feline, canine, and human strains have an identical susceptibility to drugs. • Parasites isolated from cats can infect feline, canine, and human macrophages. • Feline macrophages are permissive to strains isolated from dogs and humans. Zoonotic visceral leishmaniosis is a worldwide severe disease caused by Leishmania infantum , a protozoan that has phlebotomine sand flies as vectors and dogs as primary reservoir hosts. Over the last few decades, cats have been regarded as an indisputable piece within the ecological system in which L. infantum is maintained indefinitely. However, little is known about feline strains, including their phenotypic plasticity and infectivity. In this study, the phenotypic behaviour of seven L. infantum feline strains was compared to those of well-characterised counterparts isolated from two dogs and two humans in terms of growth profile, adaptive capacity under several stress conditions, susceptibility to antileishmanial drugs, and infectivity to host cells. Feline strains displayed a similar growth profile, survival capacity, and ability to infect feline, canine, and human monocyte-derived primary macrophages. Furthermore, multivariate cluster analysis suggested that most strains studied did not display distinctive phenotypic features. To our knowledge, this is the first study to analyse the phenotypic behaviour of feline L. infantum strains. This study brings new insights into the hypothetical role of cats as reservoir hosts of L. infantum since the parasites found in them are phenotypically identical to those of dogs and humans. However, further studies on the transmission dynamics should be encouraged to fully establish the status of cats in the maintenance of L. infantum foci. [ABSTRACT FROM AUTHOR]