Comparison of myocardial damage among dogs at different stages of clinical leishmaniasis and dogs with idiopathic chronic kidney disease.

Canine leishmaniasis (CanL) is a systemic disease caused by the protozoan parasite Leishmania infantum. Myocarditis in CanL has been described previously in CanL by histopathological analysis of post-mortem specimens and by evaluation of cardiac troponin I (cTnI) levels. However, the degree of myocardial damage at different stages of CanL and the role that concurrent azotaemia plays in this myocardial injury are unknown. The aim of this study was to prospectively evaluate and compare the presence of myocardial injury in dogs at different stages of clinical CanL and in dogs with severe idiopathic chronic kidney disease (CKD) by measuring cTnI. Forty-eight dogs were included in the study, divided into four groups: (1) group A (10 healthy dogs); (2) group B (17 dogs with CanL without renal azotaemia, classified as mild to severe in the LeishVet scheme); (3) group C (11 dogs with CanL and renal azotaemia, classified as very severe in the LeishVet scheme); and (4) group D (10 dogs with idiopathic CKD). Dogs in group C had significantly higher cTnI than dogs in groups B and D, although cTnI was also elevated in these groups. Dogs in group A had normal cTnI values. Dogs in groups D and C had similar renal IRIS classification scorers. Severe lymphoplasmocytic myocarditis and a positive real time PCR of L. infantum DNA were observed in all dogs in group C. Dogs with very severe CanL exhibit more myocardial injury than dogs with milder CanL or dogs with idiopathic CKD.

Experimental model for reproduction of canine visceral leishmaniosis by Leishmania infantum.

In this report an experimental model of Leishmania infantum (L. infantum) infection in dogs is described. The data presented are derived from an overall and comparative analysis of the clinical outcomes of three groups of dogs intravenously infected with 500,000 promastigotes on different dates (2003, 2006 and 2008). The parasites used for challenge were isolated from a dog having a patent form of leishmaniosis, classified as MCAN/ES/1996/BCN150 zymodeme MON-1. Late-log-phase promastigote forms derived from cultured amastigotes obtained from the spleen of the heavily infected hamsters were used for infection. Only one single infective dose was administered to each dog. After challenge, the animals were monitored for 12 months. To analyze the disease outcome, several biopathological, immunological and parasitological end-points were considered. The analysis of the infected dogs indicated that the development of the clinical disease was very similar in the three experimental challenges, as shown by the immune response, the parasite load and the clinical and histopathological lesions detected at necropsy. A high similarity was also observed between the disease development after the experimental challenge and the one reported to occur in endemic natural infection areas, as various degrees of susceptibility to the disease and even resistance were observed in the experimentally infected animals. We believe that this challenge model faithfully reproduces and mimics the course of a natural infection and that it could be used as a suitable tool for analyzing the efficacy of anti-Leishmania drugs and vaccines.

The inhibition of arginase by N(omega)-hydroxy-l-arginine controls the growth of Leishmania inside macrophages.

Polyamine synthesis from l-ornithine is essential for Leishmania growth. We have investigated the dependence of Leishmania infection on arginase, which generates l-ornithine, in macrophages from BALB/c, C57BL/6, and nitric oxide synthase II (NOS II)-deficient mouse strains. We have found that N(omega)-hydroxy-l-arginine (LOHA), a physiological inhibitor of arginase, controls cellular infection and also specifically inhibits arginase activity from Leishmania major and Leishmania infantum parasites. The effect was proportional to the course of infection, concentration dependent up to 100 microM, and achieved without an increase in nitrite levels of culture supernatants. Moreover, when the l-arginine metabolism of macrophages is diverted towards ornithine generation by interleukin 4-induced arginase I, parasite growth is promoted. This effect can be reversed by LOHA. Inhibition of NOS II by N(G)-methyl-l-arginine (LNMMA) restores the killing obtained in the presence of interferon (IFN)-gamma plus lipolysaccharide (LPS), whereas the nitric oxide scavenger 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-3-oxide-1-oxyl (carboxy-PTIO) was without effect. However, exogenous l-ornithine almost completely inhibits parasite killing when added in the presence of LOHA to macrophages from NOS II-deficient mice or to BALB/c-infected cells activated with IFN-gamma plus LPS. These results suggest that LOHA is an effector molecule involved in the control of Leishmania infection. In addition, macrophage arginase I induction by T helper cell type 2 cytokines could be a mechanism used by parasites to spread inside the host.