Neurological disease in human and canine leishmaniasis--clinical features and immunopathogenesis

Field-Deployable Treatments For Leishmaniasis: Intrinsic Challenges, Recent Developments and Next Steps

Leishmaniasis is a neglected tropical disease endemic primarily to low- and middle-income countries, for which there has been inadequate development of affordable, safe, and efficacious therapies. Clinical manifestations of leishmaniasis range from self-healing skin lesions to lethal visceral infection with chances of relapse. Although treatments are available, secondary effects limit their use outside the clinic and negatively impact the quality of life of patients in endemic areas. Other non-medicinal treatments, such as thermotherapies, are limited to use in patients with cutaneous leishmaniasis but not with visceral infection. Recent studies shed light to mechanisms through which Leishmania can persist by hiding in cellular safe havens, even after chemotherapies. This review focuses on exploring the cellular niches that Leishmania parasites may be leveraging to persist within the host. Also, the cellular, metabolic, and molecular implications of Leishmania infection and how those could be targeted for therapeutic purposes are discussed. Other therapies, such as those developed against cancer or for manipulation of the ferroptosis pathway, are proposed as possible treatments against leishmaniasis due to their mechanisms of action. In particular, treatments that target hematopoietic stem cells and monocytes, which have recently been found to be necessary components to sustain the infection and provide a safe niche for the parasites are discussed in this review as potential field-deployable treatments against leishmaniasis.

Increased CCL-5 (RANTES) Gene Expression in the Choroid Plexus of Dogs with Canine Leishmaniosis

Visceral canine leishmaniasis (CanL) can cause several clinical manifestations, including neurological lesions. Few reports have characterized the lesions observed in the central nervous system (CNS) during CanL; however, its pathogenesis remains unclear. The choroid plexus (CP) is a specialized structure responsible for the production and secretion of cerebrospinal fluid (CSF) and considered an interface between the peripheral immune system and CNS. It can allow the passage of inflammatory cells or pathogens and has the potential to act as a source of inflammatory mediators in several diseases. Thus, this study aimed to evaluate the role of CP as a possible route of inflammatory cells in the development of brain lesions in dogs with CanL, as well as its association with blood-CSF barrier (BCSFB) dysfunction. Samples were collected from 19 dogs that were naturally infected with CanL. We evaluated the histopathological lesions in the brain and investigated the gene expression of the cytokines. Capture enzyme-linked immunosorbent assay (ELISA) was used to evaluate the presence of the same cytokines in the CSF. Biochemical analysis was performed to compare the presence of albumin in the serum and CSF. Indirect ELISA was performed to measure the presence of anti-Leishmania antibodies in the CSF, which would suggest the disruption of the BCSFB. Histopathological evaluation of the dogs' brains revealed mild-to-severe inflammatory infiltrates, mainly in the CP and meninges. We also detected the presence of anti-Leishmania antibodies and albumin in the CSF, as well as Leishmania DNA in the CP. The gene expression of CCL-5 was increased in the CP of infected dogs compared with that of controls, and there was a tendency for the increase in the gene expression of CXCL-10. Thus, our findings confirm the disfunction of the BCSFB during CanL and suggest that the chemokines CCL-5 and CXCL-10 can be responsible for the recruitment of inflammatory cells found in CP.

Inhibiting Leishmania donovani Sterol Methyltransferase to Identify Lead Compounds Using Molecular Modelling

The recent outlook of leishmaniasis as a global public health concern coupled with the reportage of resistance and lack of efficacy of most antileishmanial drugs calls for a concerted effort to find new leads. The study combined In silico and in vitro approaches to identify novel potential synthetic small-molecule inhibitors targeting the Leishmania donovani sterol methyltransferase (LdSMT). The LdSMT enzyme in the ergosterol biosynthetic pathway is required for the parasite’s membrane fluidity, distribution of membrane proteins, and control of the cell cycle. The lack of LdSMT homologue in the human host and its conserved nature among all Leishmania parasites makes it a viable target for future antileishmanial drugs. Initially, six known inhibitors of LdSMT with IC50 < 10 μM were used to generate a pharmacophore model with a score of 0.9144 using LigandScout. The validated model was used to screen a synthetic library of 95,630 compounds obtained from InterBioScreen limited. Twenty compounds with pharmacophore fit scores above 50 were docked against the modelled three-dimensional structure of LdSMT using AutoDock Vina. Consequently, nine compounds with binding energies ranging from −7.5 to −8.7 kcal/mol were identified as potential hit molecules. Three compounds comprising STOCK6S-06707, STOCK6S-84928, and STOCK6S-65920 with respective binding energies of −8.7, −8.2, and −8.0 kcal/mol, lower than 22,26-azasterol (−7.6 kcal/mol), a known LdSMT inhibitor, were selected as plausible lead molecules. Molecular dynamics simulation studies and molecular mechanics Poisson–Boltzmann surface area calculations showed that the residues Asp25 and Trp208 were critical for ligand binding. The compounds were also predicted to have antileishmanial activity with reasonable pharmacological and toxicity profiles. When the antileishmanial activity of the three hits was evaluated in vitro against the promastigotes of L. donovani, mean half-maximal inhibitory concentrations (IC50) of 21.9 ± 1.5 μM (STOCK6S-06707), 23.5 ± 1.1 μM (STOCK6S-84928), and 118.3 ± 5.8 μM (STOCK6S-65920) were obtained. Furthermore, STOCK6S-84928 and STOCK6S-65920 inhibited the growth of Trypanosoma brucei, with IC50 of 14.3 ± 2.0 μM and 18.1 ± 1.4 μM, respectively. The identified compounds could be optimised to develop potent antileishmanial therapeutic agents.

Case Report: Leishmania and HIV Co-Diagnosis: How to Understand Medical History?

We report a case of a severe visceral leishmaniasis revealing an HIV-1 infection presenting as an acute primary infection. A young French man living in Paris with history of unprotected sex with a recent male partner and recent travel in Greece was admitted in our Infectious Diseases Department, presenting with acute febrile psychotic disorder, and positive HIV-1 serology with high viral load, very low CD4⁺ T-cells count and a western blot pattern suggesting an acute infection. The psychotic disorder was finally related to hemophagocytic lymphohistiocytosis diagnosed on bone marrow aspiration, supposedly secondary to HIV acute primary infection. The progressive worsening of pancytopenia despite antiretroviral treatment and the persistence of fever, chills and sweat led to the diagnosis of visceral leishmaniasis through bone marrow biopsy and leishmanial serology. He was treated with intravenous liposomal amphotericin B with quick improvement. We discuss the way HIV infection and visceral leishmaniasis may have interact to lead to the clinical presentation of our patient.

Role of Leishmania infantum in Meningoencephalitis of Unknown Origin in Dogs from a Canine Leishmaniosis Endemic Area

The main hypothesis for the aetiology of meningoencephalitis of unknown origin (MUO) in dogs is an autoimmune or genetic cause that is associated with a triggering event (environmental factors/infectious agents). The aim of this ambispective cohort study was to test for Leishmania infantum infection in the blood and cerebrospinal fluid (CSF) of dogs with MUO in an endemic area of canine leishmaniosis. Dogs with MUO were selected amongst all dogs undergoing blood anti-L. infantum antibody testing (control group). The blood plasma or serum samples from all dogs were analysed for anti- L. infantum antibodies by a quantitative indirect fluorescent assay (IFAT). In dogs with MUO, CSF samples were obtained for analysed by PCR detection of L. infantum DNA. Forty-four percent and 22% of the dogs in the MUO group featured magnetic resonance imaging (MRI) findings and CSF cytology respectively, consistent with L. infantum infection. IFAT, PCR, and histological findings were negative for L. infantum. A significant difference in L. infantum infection prevalence was found between the control and MUO group (p = 0.0022). While it seems unlikely that L. infantum plays a role in the aetiology of MUO, in endemic areas, this pathogen should be included in the differential diagnosis of this neurological disorder.

Leishmania infantum infection reduces the amyloid β42-stimulated NLRP3 inflammasome activation

Activation of the NLRP3 inflammasome has been shown to play a major role in the neuroinflammation that accompanies Alzheimer's disease (AD); interventions that down regulate the NLRP3 inflammasome could thus be beneficial in AD. Parasite infections were recently shown to be associated with improved cognitive functions in Apolipoprotein E4 (ApoE4)-expressing members of an Amazonian tribe. We verified in an in vitro model whether Leishmania infantum infection could reduce NLRP3. Results obtained in an initial experimental model in which PBMC were LPS primed and nigericin-stimulated showed that L. infantum infection significantly reduced ASC-speck formation (i.e. intracellular inflammasome proteins assembly), as well as the production of activated caspase 5 and IL-1β, but increased that of activated caspase 1 and IL-18. Moreover, L. infantum infection induced the generation of an anti-inflammatory milieu by suppressing the production of TNFα and increasing that of IL-10. These results were replicated when cells that had been LPS-primed were stimulated with Aβ₄₂ and infected with L. infantum. Results herein indicate that Leishmania infection favors an anti-inflammatory milieu, which includes the down-regulation of NLRP3 inflammasome activation, possibly to facilitate its survival inside host cells. A side effect of Leishmaniasis would be the hampering of neuroinflammation; this could play a protective role against AD development.

Diagnostic evaluation of the amastin protein from Leishmania infantum in canine and human visceral leishmaniasis and immunogenicity in human cells derived from patients and healthy controls

The diagnosis of visceral leishmaniasis (VL) presents problems due to the toxicity and/or high cost of drugs. In addition, no vaccine exists to protect against human disease. In this study, the antigenicity and immunogenicity of amastin protein were evaluated in L. infantum-infected dogs and humans. For the diagnosis, besides the recombinant protein, 1 linear B-cell epitope was synthetized and evaluated in serological assays. Results showed high sensitivity and specificity values to detect the disease when both antigens were employed against a canine and human serological panel. By contrast, when using rA2 and a soluble Leishmania antigenic preparation, sensitivity and specificity values proved to be lower. A preliminary immunogenicity study showed that the amastin protein induced high IFN-γ and low IL-10 production in stimulated PBMC derived from treated VL patients and healthy subjects, thus suggesting a potential use of this protein as an immunogen to protect against human disease.

Canine visceral leishmaniasis diagnosis: a comparative performance of serological and molecular tests in symptomatic and asymptomatic dogs

Although serological assays have been widely used for the diagnosis of canine visceral leishmaniasis (CVL), they present different performances depending on the clinical profile of the dogs. This study evaluated the accuracy of serological tests, immunochromatographic (Dual Path Platform: DPP®) and enzyme-linked immunosorbent (ELISA EIE®), for CVL in relation to the detection of Leishmania DNA through real-time polymerase chain reaction (real-time PCR) in samples from symptomatic and asymptomatic dogs from a non-endemic area in the state of Rio Grande do Sul, Southern Brazil. Serum from 140 dogs (39 symptomatic and 101 asymptomatic) was tested by DPP and ELISA followed by real-time PCR. From a total of 140 samples evaluated, Leishmania DNA was detected by real-time PCR in 41.4% (58/140). Moreover, 67.2% of samples positive in real-time PCR were positive in both DPP and ELISA (39/58), showing moderate agreement between methods. In the symptomatic group, one sample non-reactive in both serological assays was positive in real-time PCR, whereas in the asymptomatic group, 17.8% non-reactive or undetermined samples in serological assays were positive in the molecular method. Leishmania DNA was not detected in 17.9% reactive samples by serological assays from the symptomatic group, and in 3.9% from asymptomatic dogs. Real-time PCR demonstrated greater homogeneity between symptomatic and asymptomatic groups compared with DPP and ELISA. The molecular method can help to establish the correct CVL diagnosis, particularly in asymptomatic dogs, avoiding undesirable euthanasia.

Molecular Method Confirms Canine Leishmania Infection Detected by Serological Methods in Non-Endemic Area of Brazil

In Brazil, visceral leishmaniasis (VL) is expanding and becoming urbanized, especially in non-endemic areas such as the State of Rio Grande do Sul. Considering that infected dogs are the main reservoir for zoonotic VL, this study evaluated the prevalence of canine visceral leishmaniasis (CVL) in the metropolitan area of Porto Alegre, a new area of expansion of VL in Brazil. Serum and plasma from 405 asymptomatic dogs from the municipalities of Canoas (n=107), São Leopoldo (n=216), and Novo Hamburgo (n=82) were tested for CVL using immunochromatographic (DPP^®) and ELISA EIE^® assays (2 assays officially adopted by the Brazilian government for the diagnosis of CVL) and real-time PCR to confirm the results. There was no agreement among serological and real-time PCR results, indicating that the Leishmania infection in asymptomatic animals with low parasite load, confirmed by negative parasitological tests (smears and parasite culture), need to be evaluated by molecular methods. The prevalence of LVC in the metropolitan region of Porto Alegre, confirmed by real-time PCR was 4% (5.6% in Canoas and 4.6% in São Leopoldo). The use of molecular method is essential for accurate diagnosis of CVL, especially in asymptomatic dogs in non-endemic areas.

Unveiling Cerebral Leishmaniasis: parasites and brain inflammation in Leishmania donovani infected mice

Visceral leishmaniasis (VL) is a systemic disease with multifaceted clinical manifestations, including neurological signs, however, the involvement of the nervous system during VL is underestimated. Accordingly, we investigated both brain infection and inflammation in a mouse model of VL. Using bioluminescent Leishmania donovani and real-time 2D-3D imaging tools, we strikingly detected live parasites in the brain, where we observed a compartmentalized dual-phased inflammation pattern: an early phase during the first two weeks post-infection, with the prompt arrival of neutrophils and Ly6Chigh macrophages in an environment presenting a variety of pro-inflammatory mediators (IFN-γ, IL-1β, CXCL-10/CXCR-3, CCL-7/CCR-2), but with an intense anti-inflammatory response, led by IL-10; and a re-inflammation phase three months later, extremely pro-inflammatory, with novel upregulation of mediators, including IL-1β, TNF-α and MMP-9. These new data give support and corroborate previous studies connecting human and canine VL with neuroinflammation and blood-brain barrier disruption, and conclusively place the brain among the organs affected by this parasite. Altogether, our results provide convincing evidences that Leishmania donovani indeed infects and inflames the brain.

Neurological manifestations in dogs naturally infected by Leishmania infantum: descriptions of 10 cases and a review of the literature

In order to evaluate possible nervous system involvement in canine leishmaniasis, retrospective evaluation of all medical records of leishmaniotic dogs exhibiting neurological signs referred to our hospital over a 5-year period was performed. The records of 10 dogs were reviewed. Depending on the neuroanatomical localisation, the dogs underwent advanced diagnostic imaging, cerebrospinal fluid analysis, electrodiagnostic testing and histopathologic evaluations. The final neurological diagnosis was: meningoencephalitis (n=2), brain haemorrhagic stroke (n=1), haemorrhagic choroiditis (n=1), meningomyelitis (n=2), ischaemic myelopathy (n=1), polymyositis (n=2) and peripheral neuropathy (n=1). This study confirms that both central and peripheral nervous systems can be affected by leishmaniasis and provides an overview on the possible etiopathogenetic mechanisms. In addition, clinical and diagnostic findings, therapy and follow-up of affected dogs are described.

Analysis of microbial community composition and diversity in postoperative intracranial infection using high‑throughput sequencing

Intracranial infection is one of the most serious complications following neurosurgery. It is well acknowledged that bacteria and fungi are the main pathogens responsible for postoperative intracranial infection. However, the microbial community structure, including composition, abundance and diversity, in postoperative intracranial infection is not fully understood, which greatly compromises our understanding of the necessity and effectiveness of postoperative antibiotic treatment. The present study collected eight cerebrospinal fluid (CSF) samples from patients with intracranial infection following neurosurgical procedures. High‑throughput amplicon sequencing for 16S rDNA and internal transcribed spacer (ITS) was performed using the Illumina MiSeq platform to investigate the microbial community composition and diversity between treated and untreated patients. Bioinformatics analysis revealed that the microbial composition and diversity in each patient group (that is, with or without antibiotic treatment) was similar; however, the group receiving antibiotic treatment had a comparatively lower species abundance and diversity compared with untreated patients. At the genus level, Acinetobacter and Staphylococcus were widely distributed in CSF samples from patients with postoperative intracranial infection; in particular, Acinetobacter was detected in all CSF samples. In addition, five ITS fungal libraries were constructed, and Candida was detected in three out of four patients not receiving antibiotic treatment, indicating that the fungal infection should be given more attention. In summary, 16S and ITS high‑throughput amplicon sequencing were practical methods to identify pathogens in the different periods of treatment in patients with postoperative intracranial infection. There was a notable difference in microbial composition and diversity between the treated and untreated patients. Alterations in the microbial community structure may provide a signal whether antibiotic treatment worked in postoperative intracranial infection and may assist surgeons to better control the progression of infection.

Occurrence of Leishmania infantum in the central nervous system of naturally infected dogs: Parasite load, viability, co-infections and histological alterations

Zoonotic visceral leishmaniasis is caused by the protozoan Leishmania infantum and little is known about the occurrence and pathogenesis of this parasite in the CNS. The aims of this study were to evaluate the occurrence, viability and load of L. infantum in the CNS, and to identify the neurological histological alterations associated with this protozoan and its co-infections in naturally infected dogs. Forty-eight Leishmania-seropositive dogs from which L. infantum was isolated after necropsy were examined. Cerebrospinal fluid (CSF) samples were analyzed by parasitological culture, quantitative real-time PCR (qPCR) and the rapid immunochromatographic Dual Path Platform test. Brain, spinal cord and spleen samples were submitted to parasitological culture, qPCR, and histological techniques. Additionally, anti-Toxoplasma gondii and anti-Ehrlichia canis antibodies in serum and distemper virus antigens in CSF were investigated. None of the dogs showed neurological signs. All dogs tested positive for L. infantum in the CNS. Viable forms of L. infantum were isolated from CSF, brain and spinal cord in 25% of the dogs. Anti-L. infantum antibodies were detected in CSF in 61% of 36 dogs. Inflammatory histological alterations were observed in the CNS of 31% of the animals; of these, 66% were seropositive for E. canis and/or T. gondii. Amastigote forms were associated with granulomatous non-suppurative encephalomyelitis in a dog without evidence of co-infections. The highest frequency of L. infantum DNA was observed in the brain (98%), followed by the spinal cord (96%), spleen (95%), and CSF (50%). The highest L. infantum load in CNS was found in the spinal cord. These results demonstrate that L. infantum can cross the blood-brain barrier, spread through CSF, and cause active infection in the entire CNS of dogs. Additionally, L. infantum can cause inflammation in the CNS that can lead to neurological signs with progression of the disease.

Visceral leishmaniasis: a forgotten epidemic

Visceral leishmaniasis (VL or kala-azar) is most endemic in Asia and Africa and commonly affects young children. It is usually caused by Leishmania donovani or Leishmania infantum that are transmitted by Phlebotomine sand flies. Transmission may be anthroponotic or zoonotic or both, depending on the endemic area. Clinical features include fever, hepatosplenomegaly, weight loss and pancytopenia. Younger age, malnutrition and immunosuppression (HIV infection, use of immunosuppressive drugs) are risk factors. Many infections remain asymptomatic. Diagnosis is made by demonstration of the Leishmania parasite in aspirates of lymph node, bone marrow or spleen. Serological tests such as rK39 strip test are widely used but the sensitivity varies. qPCR is useful to detect low numbers of parasites and to monitor treatment. Treatment is with AmBisome monotherapy in most areas but with drug combinations elsewhere. HIV co-infected patients are most difficult to treat and often relapse. Control efforts focus on case finding, availability of diagnostic tools, reservoir control and protection from sand flies (insecticides, bed nets). There is no human vaccine.