In this work, we investigated the association between the disruption of splenic lymphoid tissue and the severity of visceral leishmaniasis in dogs. Clinical and laboratory data from 206 dogs were reviewed. Spleen sections collected during the euthanasia of these animals were analyzed, and the splenic lymphoid tissue samples were classified as well organized (spleen type 1), slightly disorganized (spleen type 2), or moderately to extensively disorganized (spleen type 3). Of 199 dogs with evidence of Leishmania infection, 54 (27%) had spleen type 1, 99 (50%) had spleen type 2, and 46 (23%) had spleen type 3. The number of clinical signs associated with visceral leishmaniasis was significantly higher in the animals with evidence of Leishmania infection and spleen type 2 or 3 than in the animals with spleen type 1. Alopecia, anemia, dehydration, dermatitis, lymphadenopathy, and onychogryphosis were all more frequent among animals with evidence of Leishmania infection and spleen type 3 than among the dogs with evidence of Leishmania infection and spleen type 1. The association between the severity of canine visceral leishmaniasis and the disorganization of the splenic lymphoid tissue was even more evident in the group of animals with positive spleen culture. Conjunctivitis and ulceration were also more common in the animals with spleen type 3 than in the animals with spleen type 1. The serum levels (median, interquartile range) of albumin (1.8, 1.4–2.3 g/dL) and creatinine (0.7, 0.4–0.8 mg/dL) were significantly lower and the serum levels of aspartate aminotransferase were significantly higher (57, 39–95 U) in animals with spleen type 3 than in animals with spleen type 1 (2.8, 2.4–3.4 g/dL; 0.9, 0.7–1.2 mg/dL and 23, 20–32 U, respectively). Our data confirm the hypothesis that disruption of the splenic lymphoid tissue is associated with a more severe clinical presentation of canine visceral leishmaniasis.

Visceral leishmaniasis (VL) is a neglected tropical disease (NTD), caused by the intracellular protozoan parasites Leishmania donovani and Leishmania infantum. Symptomatic VL is considered fatal when left untreated. At present, there is no effective vaccine licensed for human use and available chemotherapies have limitations. Understanding the local immune mechanisms required for the control of infection is a key factor for developing effective vaccines and therapeutics. We have investigated the development of the typical granulomatous lesions in the liver in experimental VL over time, together with the local immune responses. BALB/c mice were infected intravenously with a dose of 2 × 107 L. donovani amastigotes (MHOM/ET/67/HU3) and sacrificed at 15, 35 and 63 days post-infection (dpi). Histopathology and immunohistochemical techniques were used for the detection of Leishmania antigen, selected cell types including B and T lymphocytes, macrophages and neutrophils (CD45R-B220+, CD3+, F4/80+ and Ly-6G+) and iNOS. Granulomatous lesions were identified as early as 15 dpi in the livers of all infected animals. Three categories were used to classify liver granulomas (immature, mature and clear). Clear granulomas were exclusively detected from 35 dpi onwards. Kupffer cells (F4/80+) were predominant in immature granulomas, regardless of the dpi. Nonetheless, the highest expression was found 63 dpi. Positive staining for iNOS was mainly observed in the cytoplasm of fused Kupffer cells and the highest expression observed at 35 dpi. T cells (CD3+) and B cells (CD45R-B220+) were predominant in more advanced granuloma stages, probably related to the establishment of acquired immunity. Neutrophils (Ly-6G+) were predominantly observed in mature granulomas with the highest expression at 15 dpi. Neutrophils were lower in numbers compared to other cell types, particularly at later time points. Our results reflect the role of macrophages during the early stage of infection and the establishment of a lymphocytic response to control the infection in more advanced stages.

Background: The liver plays a central role in the development of canine visceral leishmaniasis. Studies of natural infection in animals and humans indicate a direct relationship between resolution of infection and the formation and maturation of granulomas in the liver. However, in contrast to other reports in the literature, the present study found no differences in the characteristics of hepatic granulomas that could be related to resistance or susceptibility to Leishmania. Here, we describe the hepatic alterations observed in dogs with differing clinical manifestations of visceral leishmaniasis in an endemic area in the state of Bahia, Brazil. Methods: We examined 148 animals in an endemic area. The animals were clinically examined, and the infection was determined by ELISA, spleen aspirate culture and quantitative PCR. The animals were grouped into asymptomatic or symptomatic based on the number of signs of LV. The histological liver evaluation was performed in a blinded way. Results: Our results indicated no association between the characteristics of granulomas and clinical presentation. We found an association between the intensity of this inflammatory response and parasite load in the animals’ spleens. It is important to note that while hepatic alterations, such as portal and perivascular inflammation and the presence of larger amounts of granulomas, were linked with higher parasite loads, we found the inverse to be true with respect to intrasinusoidal lymphocytosis, the formation of intrasinusoidal inflammatory cell aggregates and Kupffer cell hypertrophy. Conclusions: Our findings suggest that the presence of mononuclear inflammatory cells inside the sinusoids is more important than that of organized granulomas in terms of the containment of parasitism by the host. We suggest that the presence of granulomas indicates the failure of a first line of defense mechanism in the control of parasite infection, which could be related to the presence of inflammatory cells and Kupffer cell hypertrophy inside the sinusoids. We further demonstrated that dogs with active Leishmania spp. infection present a higher frequency of inflammatory changes in the liver. In addition to being correlated with the severity of clinical manifestation, these hepatic alterations were also associated with changes in hematological and biochemical parameters.

Visceral leishmaniasis is associated with a variety of hematological abnormalities. In this study, we correlated the hematological changes in the peripheral blood of dogs naturally infected with Leishmania infantum (L. infantum) with the distribution of cell lineages and cytokine gene expression patterns in the bone marrow. Samples from 63 naturally semidomiciled dogs living in an endemic area of visceral leishmaniasis were analyzed. L. infantum infection was detected in 50 dogs (79.3%). Among those, 18 (32%) had positive splenic cultures and showed more clinical signs. They also had lower red blood cell counts and leukocytosis with an increased number of neutrophils and monocytes in peripheral blood compared to dogs negative to this test. L. infantum DNA was detected in the bone marrow of 8/14 dogs with positive splenic culture. Dogs with L. infantum infection in the bone marrow presented with histiocytosis (p = 0.0046), fewer erythroid cell clusters (p = 0.0127) and increased gene expression levels of IFN-γ (p = 0.0015) and TNF (p = 0.0091). The data shown herein suggest that inflammatory and cytokine gene expression changes in bone marrow may contribute to the peripheral blood hematological changes observed in visceral leishmaniasis.

Oleylphosphocholine (OlPC) is a miltefosine derivative that is more effective than miltefosine against Leishmania infections in rodent models. Because canines are a natural host for Leishmania, the improved treatment of canine leishmaniasis is essential both for veterinary medicine and as a large animal model for clinical development. Oleylphosphocholine, at a dosage of 4 mg/kg/day for 28 days, was compared with the approved canine regimen of miltefosine at a dosage of 2 mg/kg/day for 28 days in 33 naturally infected Brazilian dogs (17 randomly assigned to receive OlPC versus 16 designated to receive miltefosine). The animals were followed for 5 months posttreatment. The primary endpoint was the clinical score, which was calculated as the sum of scores for each of 23 clinical parameters graded 0 (normal), 1 (somewhat abnormal), or 2 (markedly abnormal) by a blinded observer. A higher clinical score signified more severe disease. The mean (SD) clinical scores for the OlPC versus miltefosine groups are as follows: pretherapy, 10.1 (5.6) versus 7.7 (4.5; P = 0.19); 3 months posttherapy, 4.3 (4.1) versus 9.5 (4.9; P <0.01); 5 months posttherapy, 3.9 (3.8) versus 8.9 (4.7; P <0.01). Scores for lymph nodes, ear crusts, and splenic parasites were statistically lower for the OlPC group versus the miltefosine group, suggesting that both visceral and cutaneous parameters contributed to OlPC’s statistically greater efficacy. One OlPC animal, with minimal splenic parasites pretreatment and zero parasites at the end of treatment, died of kidney failure due to immune-complex deposition, which was presumably already present pretreatment. The increase in blood creatinine values observed in OlPC animals warrants further study in future experiments. The superior clinical effect of OlPC in comparison to miltefosine in this canine study primes OlPC for development as an oral treatment for canine and human leishmaniasis.

Background: Leishmaniasis is a significant global public health issue that is caused by parasites from Leishmania genus. With limited treatment options and rising drug resistance, there is a pressing need for new therapeutic approaches. Molecular chaperones, particularly Hsp90, play a crucial role in parasite biology and are emerging as promising targets for drug development. Objective: This study evaluates the efficacy of 17-DMAG in treating BALB/c mice from cutaneous leishmaniasis through in vitro and in vivo approaches. Materials and Methods: We assessed 17-DMAG’s cytotoxic effect on bone marrow-derived macrophages (BMMΦ) and its effects against L. braziliensis promastigotes and intracellular amastigotes. Additionally, we tested the compound’s efficacy in BALB/c mice infected with L. braziliensis via intraperitoneal administration to evaluate the reduction in lesion size and the decrease in parasite load in the ears and lymph nodes of infected animals. Results: 17-DMAG showed selective toxicity [selective index = 432) towards Leishmania amastigotes, causing minimal damage to host cells. The treatment significantly reduced lesion sizes in mice and resulted in parasite clearance from ears and lymph nodes. It also diminished inflammatory responses and reduced the release of pro-inflammatory cytokines (IL-6, IFN-γ, TNF) and the regulatory cytokine IL-10, underscoring its dual leishmanicidal and anti-inflammatory properties. Conclusions: Our findings confirm the potential of 17-DMAG as a viable treatment for cutaneous leishmaniasis and support further research into its mechanisms and potential applications against other infectious diseases.