Virulence of Leishmania infantum is expressed as a clonal and dominant phenotype in experimental infections

Impact of collaborative actions of Leishmania (Viannia) braziliensis subpopulations on the infection profile

This study focuses on the role of the population structure of Leishmania spp. on the adaptive capacity of the parasite. Herein, we investigate the contribution of subpopulations of the L. (V.) braziliensis Thor strain (Thor03, Thor10 and Thor22) in the profile of murine macrophages infection. Infection assays were performed with binary combinations of these subpopulations at stationary phases. The initial interaction time showed major effects on the combination assays, as demonstrated by the significant increase in the infection rate at 5 h. Based on the endocytic index (EI), Thor10 (EI = 563.6) and Thor03 (EI = 497) showed a higher infection load compared to Thor22 (EI = 227.3). However, the EI decreased in Thor03 after 48 h (EI = 447) and 72 h (EI = 388.3) of infection, and showed changes in the infection level in all Thor10/Thor22 combinations. Assays with CellTrace CFSE-labelled Thor22 promastigotes indicated an increase (~1.5 fold) in infection by this subpopulation in the presence of Thor10 when compared to the infection profile of Thor03/Thor22 combinations in the same proportions. In addition, the potential of these subpopulations, alone or in binary combinations, to modulate the expression of cytokines and nitric oxide (NO) in vitro was investigated. Lower NO and tumour necrosis factor-α production levels were observed for all Thor10/Thor22 combinations at 24 h compared to these subpopulations alone. In contrast, Thor03/Thor22 combination assays increased IL-10 production at this time. Collectively, these results provide in vitro evidence on the potential of L. (V.) braziliensis population structure to play a relevant role in a host infection by this parasite.

Evaluation of cytochrome b sequence to identify Leishmania species and variants: the case of Panama

BACKGROUND

The genetic heterogeneity of Leishmania parasites is a major factor responsible for the wide variety of Leishmania-associated manifestations. Consequently, understanding the genetic make-up of Leishmania species using suitable molecular markers is an important component of realising local and regional scale disease risk. The cytochrome b (cytb) is frequently used to type New World Leishmania species. However, its potential to discriminate Leishmania species and variants requires further evaluation.

OBJECTIVES

To explore the capacity of cytb gene to identify New World Leishmania species and variants and to develop an approach able to type local Leishmania species and variants.

METHODS

We retrieved 360 partial and complete Leishmania cytb gene sequences publicly available in GenBank database to study all single nucleotide polymorphisms (SNPs) across the cytb gene that differentiate New World Leishmania species. This information was used to develop an approach based upon the polymorphisms found in a DNA segment of 948bp. We also compared the typing results found with this technique with the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) profiling obtained using HSP70 gene as target. One hundred Panamanian isolates were used to both typed Leishmania species and assess local genetic variability.

FINDINGS

We found complete agreement between our cytb approach and the PCR-RFLP profiling method based on HSP70 for Leishmania species identification. Ninety-two isolates were identified as L. panamensis, although other Viannia species were found circulating at a lower frequency. Three L. panamensis haplotypes were identified in Panamanian provinces. We also provide an initial report of L. guyanensis haplotypes circulating in Panama.

MAIN CONCLUSIONS

Cytb gene sequence encompasses key main SNPs that aid to identify Leishmania species. The cytb approach developed with this information was able to identify and assess genetic variability of local Leishmania species found in this study.

High Content Analysis of Macrophage-Targeting EhPIb-Compounds against Cutaneous and Visceral Leishmania Species

An immunostimulatory glycolipid molecule from the intestinal protozoan parasite Entamoeba histolytica (Eh) and its synthetic analogs derived from its phosphatidylinositol-b-anchor (EhPIb) previously showed considerable immunotherapeutic effects against Leishmania major infection in vitro and in vivo. Here, we describe a high content screening assay, based on primary murine macrophages. Parasites detection is based on a 90 kDA heat shock protein-specific staining, enabling the detection of several Leishmania species. We validated the assay using L. major, L. braziliensis, L. donovani, and L. infantum as well as investigated the anti-leishmanial activity of six immunostimulatory EhPIb-compounds (Eh-1 to Eh-6). Macrophages infected with dermotropic species were more sensitive towards treatment with the compounds as their viability showed a stronger reduction compared to macrophages infected with viscerotropic species. Most compounds caused a significant reduction of the infection rates and the parasite burdens depending on the infecting species. Only compound Eh-6 was found to have activity against all Leishmania species. Considering the challenges in anti-leishmanial drug discovery, we developed a multi-species screening assay capable of utilizing non-recombinant parasite strains, and demonstrated its usefulness by screening macrophage-targeting EhPIb-compounds showing their potential for the treatment of cutaneous and visceral leishmaniasis.

Phenotype evaluation of human and canine isolates of Leishmania infantum

Human visceral leishmaniasis (VL) and canine leishmaniasis (CanL) in countries of South and Central America are caused by Leishmania infantum and has been endemic in Brazil for several years. The parasite biodiversity as well as the pharmacologic properties of drugs and the host species, are involved in the efficacy or inefficacy of leishmaniasis treatments. Although there are substantial number of reports describing the genetic characterization of the clinical field isolates of L. infantum,the phenotypic parameters have been less studied. In this study isolates from human and canine leishmaniasis (Hum1 and Can1) obtained in Campinas, São Paulo state, Brazil were identified as L. infantum. The Hum1 and Can1 isolates exhibited typical promastigote growth pattern. Regarding morphological features Can1 isolate differed in cell size. The infectivity in vitro of both isolatesis lower compared to the reference strain of L. infantum. Moreover, the in vivo infectivity of the three parasites is similar in Balb/c mice. The Hum1 isolate is more sensitive to leishmanial drugs (amphotericin B, miltefosine and glucantime) than the Can1 isolate when inside human macrophages, but not when inside canine macrophages. These findings indicated that L. infantum isolates differs in some phenotypic characteristics.

Experimental Cutaneous Leishmaniasis: Mouse Models for Resolution of Inflammation Versus Chronicity of Disease

Experimental cutaneous leishmaniasis of mice is a valuable model to study the immune response to the protozoan pathogen Leishmania and to define mechanisms of parasite control and resolution of inflammation as well as of parasite evasion and chronicity of disease. In addition, over many years Leishmania-infected mice have been successfully used to analyze the function of newly discovered immune cell types, transcription factors, cytokines, and effector mechanisms in vivo. In this chapter we present detailed protocols for the culture, propagation, and inoculation of Leishmania promastigotes, the monitoring of the course of cutaneous infection, the determination of the tissue parasite burden and for the phenotyping of the ensuing immune response. The focus lies on the L. major mouse model, but an overview on other established models of murine cutaneous leishmaniasis is also provided.

Elucidating in vitro and in vivo phenotypic behaviour of L. infantum/L. major natural hybrids

The clinical manifestation and course of Leishmania infections depend on factors such as species, virulence and host-immunity. Although trypanosomatids are considered to have clonal propagation, genetic hybridization has produced successful natural hybrid lineages. Hybrids displaying strong selective advantages may have an impact on pathogenesis and the eco-epidemiology of leishmaniasis. Thus, characterization of phenotypic properties of Leishmania hybrids could bring significant insight into the biology, infectivity, pathogenicity and transmission dynamics of these atypical strains. The present study focuses on phenotypic features and survival capacity of Leishmania infantum/Leishmania major hybrid isolates as compared with representative putative parental species, L. infantum and L. major. In vitro assays (growth kinetics, susceptibility to different conditions) and in vivo infection (parasite detection and histopathological alterations) showed that hybrids present higher growth capacity and decreased susceptibility to reactive oxygen species. Furthermore, evaluation of infected spleen tissue suggests that hybrids induce a stronger immune reaction than their putative parents, leading to the development of white pulp hyperplasia in B-lymphocyte compartments. Overall, these hybrids have shown high plasticity in terms of their general behaviour within the different phenotypic parameters, suggesting that they might have acquired genetic features conferring different mechanisms to evade host cells.

Evidence of Subpopulations with Distinct Biological Features Within a Leishmania (Viannia) braziliensis Strain

The present study demonstrates that the Leishmania (Viannia) braziliensis strain MCAN/BR/1998/R619 is composed of multiple subpopulations with measurable distinctions. Single parasites were separated from a culture of promastigotes in stationary phase by cell sorting and then cultivated as subpopulations. Subsequently, these subpopulations were evaluated for features of in vitro growth, infectivity to murine macrophages and proteinase gene expression. The first evidence of distinct characteristics was observed during the in vitro cultivation of isolated subpopulations, as distinct clusters of patterns were formed among the cultures, indicating the existence of quantifiable fluctuations in metrics. Further, when infecting murine macrophages, the subpopulations induced distinct patterns of production of immune response mediators. While some subpopulations mainly induced the production of IL-1β, IL-6 and TNF-α, others induced the production of IL-12p70 and nitric oxide. Finally, amastigotes of these subpopulations had higher expression of proteinase genes than promastigotes. Additionally, cysteine proteinase, serine proteinase, metalloproteinase and aspartic proteinases were differentially expressed in promastigote and amastigote forms. These data suggest the existence of distinct profiles for the L. (V.) braziliensis MCAN/BR/1998/R619 strain and subpopulations that could drive the success of parasite adaptation to the environments that they inhabit.

Effects of trans-stilbene and terphenyl compounds on different strains of Leishmania and on cytokines production from infected macrophages

Most of the antileishmanial modern therapies are not satisfactory due to high toxicity or emergence of resistance and high cost of treatment. Previously, we observed that two compounds of a small library of trans-stilbene and terphenyl derivatives, ST18 and TR4, presented the best activity and safety profiles against Leishmania infantum promastigotes and amastigotes. In the present study we evaluated the effects of ST18 and the TR4 in 6 different species of Leishmania and the modifications induced by these two compounds in the production of 8 different cytokines from infected macrophages. We observed that TR4 was potently active in all Leishmania species tested in the study showing a leishmanicidal activity higher than that of ST18 and meglumine antimoniate in the most of the species. Moreover, TR4 was able to decrease the levels of IL-10, a cytokine able to render the host macrophage inactive allowing the persistence of parasites inside its phagolysosome, and increase the levels of IL-1β, a cytokine important for host resistance to Leishmania infection by inducible iNOS-mediated production of NO, and IL-18, a cytokine implicated in the development of Th1-type immune response.

Generation of Paramoeba perurans clonal cultures using flow cytometry and confirmation of virulence

Amoebic gill disease (AGD) in farmed Atlantic salmon is caused by the amoeba Paramoeba perurans. The recent establishment of in vitro culture techniques for P. perurans has provided a valuable tool for studying the parasite in detail. In this study, flow cytometry was used to generate clonal cultures from single-sorted amoeba, and these were used to successfully establish AGD in experimental Atlantic salmon. The clonal cultures displayed differences in virulence, based on gill scores. The P. perurans load on gills, determined by qPCR analysis, showed a positive relationship with gill score, and with clonal virulence, indicating that the ability of amoebae to proliferate and/or remain attached on gills may play a role in virulence. Gill scores based on gross signs and histopathological analysis were in agreement. No association between level of gill score and specific gill arch was observed. It was found that for fish with lower gill scores based on histopathological examination, gross examination and qPCR analysis of gills from the same fish were less successful in detecting lesions and amoebae, respectively.

Phenotypic diversity and selection maintain Leishmania amazonensis infectivity in BALB/c mouse model

Leishmania are protozoan parasites that show remarkable diversity, as revealed by the various clinical forms of leishmaniasis, which can range from mild skin lesions to severe metastatic cutaneous/mucosal lesions. The exact nature and extent of Leishmania phenotypic diversity in establishing infection is not fully understood. In order to try to understand some aspects of this diversity, we subcutaneously infected BALB/c mice with first and second generation subclones of a L. amazonensis strain isolated from a patient (BA125) and examined in vivo lesion growth rate and antimony susceptibility. In vivo fast-, medium- and slow-growing subclones were obtained; moreover, fast-growing subclones could generate slow-growing subclones and inversely, revealing the continuous generation of diversity after passage into mice. No antimony-resistant subclone appeared, probably a rare occurrence. By tagging subclone cells with a L. amazonensis genomic cosmid library, we found that only a very small number of founding cells could produce lesions. Leishmania clones transfected with in vivo selected individual cosmids were also diverse in terms of lesion growth rate, revealing the cosmid-independent intrinsic characteristics of each clone. Our results suggest that only a few of the infecting parasites are able to grow and produce lesions; later, within the cell mixture of each lesion, there coexist several parasite populations with different potentialities to grow lesions during the next infection round. This may reflect a sort of programmed heterogeneity of individual parasites, favoring the survival of some individuals in various environmental conditions.

A Telomeric Cluster of Antimony Resistance Genes on Chromosome 34 of Leishmania infantum

The mechanisms underlying the drug resistance of Leishmania spp. are manifold and not completely identified. Apart from the highly conserved multidrug resistance gene family known from higher eukaryotes, Leishmania spp. also possess genus-specific resistance marker genes. One of them, ARM58, was first identified in Leishmania braziliensis using a functional cloning approach, and its domain structure was characterized in L. infantum Here we report that L. infantum ARM58 is part of a gene cluster at the telomeric end of chromosome 34 also comprising the neighboring genes ARM56 and HSP23. We show that overexpression of all three genes can confer antimony resistance to intracellular amastigotes. Upon overexpression in L. donovani, ARM58 and ARM56 are secreted via exosomes, suggesting a scavenger/secretion mechanism of action. Using a combination of functional cloning and next-generation sequencing, we found that the gene cluster was selected only under antimonyl tartrate challenge and weakly under Cu(2+) challenge but not under sodium arsenite, Cd(2+), or miltefosine challenge. The selective advantage is less pronounced in intracellular amastigotes treated with the sodium stibogluconate, possibly due to the known macrophage-stimulatory activity of this drug, against which these resistance markers may not be active. Our data point to the specificity of these three genes for antimony resistance.

Leishmania infantum Genetic Diversity and Lutzomyia longipalpis Mitochondrial Haplotypes in Brazil

Leishmania infantum is the etiological agent of visceral leishmaniasis (VL) in the Americas with domestic dogs being its major reservoir hosts. The main VL vector is the sandfly Lutzomyia longipalpis, while other Lutzomyia species may play a role in disease transmission. Although the genetic structure of L. infantum populations has been widely evaluated, only a few studies have addressed this subject coupled to the genetic structure of the respective sandfly vectors. In this study, we analyzed the population structure of L. infantum in three major VL endemic areas in Brazil and associated it with Lutzomyia longipalpis geographic structure.

Study of Leishmania pathogenesis in mice: experimental considerations

Although leishmaniases are endemic in 98 countries, they are still considered neglected tropical diseases. Leishmaniases are characterized by the emergence of new virulent and asymptomatic strains of Leishmania spp. and, as a consequence, by a very diverse clinical spectrum. To fight more efficiently these parasites, the mechanisms of host defense and of parasite virulence need to be thoroughly investigated. To this aim, animal models are widely used. However, the results obtained with these models are influenced by several experimental parameters, such as the mouse genetic background, parasite genotype, inoculation route/infection site, parasite dose and phlebotome saliva. In this review, we propose an update on their influence in the two main clinical forms of the disease: cutaneous and visceral leishmaniases.

Molecular descriptors calculation as a tool in the analysis of the antileishmanial activity achieved by two series of diselenide derivatives. An insight into its potential action mechanism

A molecular modeling study has been carried out on two previously reported series of symmetric diselenide derivatives that show remarkable antileishmanial in vitro activity against Leishmania infantum intracellular amastigotes and in infected macrophages (THP-1 cells), in addition to showing favorable selectivity indices. Series 1 consists of compounds that can be considered as central scaffold constructed with a diaryl/dialkylaryl diselenide central nucleus, decorated with different substituents located on the aryl rings. Series 2 consists of compounds constructed over a diaryl diselenide central nucleus, decorated in 4 and 4' positions with an aryl or heteroaryl sulfonamide fragment, thus forming the diselenosulfonamide derivatives. With regard to the diselenosulfonamide derivatives (2 series), the activity can be related, as a first approximation, with (a) the ability to release bis(4-aminophenyl) diselenide, the common fragment which can be ultimately responsible for the activity of the compounds. (b) the anti-parasitic activity achieved by the sulfonamide pharmacophore present in the analyzed derivatives. The data that support this connection include the topography of the molecules, the conformational behavior of the compounds, which influences the bond order, as well as the accessibility of the hydrolysis point, and possibly the hydrophobicity and polarizability of the compounds.

Finding of leishmanicidal activity of 14-hydroxylunularin in mice experimentally infected with Leishmania infantum

In this study, we report the in vivo efficacy of 14-hydroxylunularin evaluated in BALB/c mice experimentally infected with promastigotes of Leishmania infantum (syn L. chagasi), the major causative agent of visceral leishmaniasis in Latin America. Seven days post-infection, treatment with 14-hydroxylunularin started and it was administered by oral and subcutaneous routes in doses of 10 and 25 mg/kg of weight for ten days using Glucantime® as reference drug. In the liver, the evaluated compound showed parasite reduction above 90% by both administration routes being the oral route the most effective at both doses. Significant decreased numbers of parasites were also observed when the treated group was compared with the control group (p≤0.05). The subcutaneous route presented a remarkable difference with at least 80% parasite suppression in liver and spleen at 10 mg/kg dose and 90% in liver at 25 mg/kg. The leishmanicidal activity of 14-hydroxylunularin against L. infantum revealed by this study is another evidence in favor of this compound as a potential candidate for the development of a new oral treatment for leishmaniasis.

Polymorphisms and ambiguous sites present in DNA sequences of Leishmania clones: looking closer

In genetic studies of Leishmania parasites, co-dominant markers are chosen for their ability to detect heterozygous polymorphisms, to infer the occurrence of inbreeding and to resolve genetic variability. The majority of DNA sequence based reports perform conventional dye terminator cycle sequencing where perfectly ambiguous sites or double peaks in the chromatogram are interpreted as heterozygous strains. However, molecular peculiarities of the parasite such as aneuploidy, mixed populations and homologous recombination advise that data from regular DNA sequence analysis should be carefully evaluated. We report here a closer look at ambiguous sites observed in 6pgd DNA sequences obtained for a multilocus sequence analysis project on Leishmania (Viannia) strains. After comparing 286 DNA sequences from biological and molecular clones of six L. (Viannia) strains we could distinguish events that contribute to genetic variation in Leishmania (recombination, mutation, chromosomal mosaics). Also, the results suggest how diversity might not be completely revealed through regular DNA sequence analysis and demonstrate the importance for molecular epidemiology research to be aware of such possibilities while choosing samples for studies.

A novel marker, ARM58, confers antimony resistance to Leishmania spp

Protozoa of the Leishmania genus cause a variety of disease forms that rank at the top of the list of neglected tropical diseases. Anti-leishmanial drugs based on pentavalent antimony have been the mainstay of therapy for over 60 years and resistance against them is increasingly encountered in the field. The biochemical basis for this is poorly understood and likely diverse. No stringent correlation between genetic markers and antimony resistance has so far been shown, prompting us to use a functional cloning approach to identify markers of resistance. Using gene libraries derived from drug-resistant and drug-sensitive Leishmania braziliensis clinical isolates in a functional cloning strategy, we repeatedly selected one gene locus located on chromosome 20 whose amplification confers increased antimony (III) resistance in vitro to an otherwise sensitive L. braziliensis clone. The gene responsible for the effect encodes a previously hypothetical protein that we dubbed LbrARM58. It comprises four repeats of a domain of unknown function, DUF1935, one of them harbouring a potential trans-membrane domain. The gene is so far unique to the Leishmania genus, while a structurally related gene without antimony resistance functionality is also found in Trypanosoma spp. Overexpression of LbrARM58 also confers antimony resistance to promastigotes and intracellular amastigotes of the related species Leishmania infantum, indicating a conserved function in Old World and New World Leishmania species. Our results also show that in spite of their RNAi system, L. braziliensis promastigotes can serve as acceptor cells for episomally propagated cosmid libraries, at least for the initial stages of functional cloning efforts.

Reduced antimony accumulation in ARM58-overexpressing Leishmania infantum

Antimony-based drugs are still the mainstay of chemotherapy against Leishmania infections in many countries where the parasites are endemic. The efficacy of antimonials has been compromised by increasing numbers of resistant infections, the basis of which is not fully understood and likely involves multiple factors. By using a functional cloning strategy, we recently identified a novel antimony resistance marker, ARM58, from the parasite Leishmania braziliensis that protects the parasites against antimony-based antileishmanial compounds. Here we show that the Leishmania infantum homologue also confers resistance against antimony but not against other antileishmanial drugs and that its function depends critically on one of four conserved domains of unknown function. This critical domain requires at least two hydrophobic amino acids and is predicted to form a transmembrane structure. Overexpression of ARM58 in antimony-exposed parasites reduces the intracellular Sb accumulation by over 70%, indicating a role for ARM58 in Sb extrusion pathways, but without involvement of energy-dependent transporter proteins.

New insights on taxonomy, phylogeny and population genetics of Leishmania (Viannia) parasites based on multilocus sequence analysis

The Leishmania genus comprises up to 35 species, some with status still under discussion. The multilocus sequence typing (MLST)--extensively used for bacteria--has been proposed for pathogenic trypanosomatids. For Leishmania, however, a detailed analysis and revision on the taxonomy is still required. We have partially sequenced four housekeeping genes--glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), mannose phosphate isomerase (MPI) and isocitrate dehydrogenase (ICD)--from 96 Leishmania (Viannia) strains and assessed their discriminatory typing capacity. The fragments had different degrees of diversity, and are thus suitable to be used in combination for intra- and inter-specific inferences. Species-specific single nucleotide polymorphisms were detected, but not for all species; ambiguous sites indicating heterozygosis were observed, as well as the putative homozygous donor. A large number of haplotypes were detected for each marker; for 6PGD a possible ancestral allele for L. (Viannia) was found. Maximum parsimony-based haplotype networks were built. Strains of different species, as identified by multilocus enzyme electrophoresis (MLEE), formed separated clusters in each network, with exceptions. NeighborNet of concatenated sequences confirmed species-specific clusters, suggesting recombination occurring in L. braziliensis and L. guyanensis. Phylogenetic analysis indicates L. lainsoni and L. naiffi as the most divergent species and does not support L. shawi as a distinct species, placing it in the L. guyanensis cluster. BURST analysis resulted in six clonal complexes (CC), corresponding to distinct species. The L. braziliensis strains evaluated correspond to one widely geographically distributed CC and another restricted to one endemic area. This study demonstrates the value of systematic multilocus sequence analysis (MLSA) for determining intra- and inter-species relationships and presents an approach to validate the species status of some entities. Furthermore, it contributes to the phylogeny of L. (Viannia) and might be helpful for epidemiological and population genetics analysis based on haplotype/diplotype determinations and inferences.

[Visceral leishmaniasis in immunocompetent adults. About six cases]

OBJECTIVE

Studying the epidemiological variations of visceral leishmaniasis in Tunisia and proving the importance of parasitological investigations to raise the diagnosis.

PATIENTS AND METHODS

Six patients hospitalised during the period between January 1998 and January 2009 at Fattouma Bourguiba Teaching Hospital in Monastir, five men and an only one woman, aged from 26 to 70 years old, originating from the central and eastern regions of the country. Epidemiological, clinical, biological and therapeutic data were obtained from the patient's medical files.

RESULTS

The major clinical symptoms were fever, weakness and spleen enlargement. Biological data revealed the presence of anaemia in every case and leucopoenia associated or not associated with thrombopenia in four cases. The diagnosis of visceral leishmaniasis was confirmed by the identification of the parasite in the blood or in the bone marrow. All patients were treated with two courses of antimoniate of meglumine separated by a 6-week interval. The outcome was positive and the patients were cured.

CONCLUSION

Visceral leishmaniasis is increasing among adults in Tunisia. Moreover, it is spreading outside its epidemiological area in the north to reach the central and southern regions. It should be raised when fever and spleen enlargement occur. Biological data are hardly specific. Diagnosis is based on finding the parasite in human fluids, mainly by molecular techniques. The rapid establishment of a specific treatment is vital.

Antimony resistance in leishmania, focusing on experimental research

Leishmaniases are parasitic diseases that spread in many countries with a prevalence of 12 million cases. There are few available treatments and antimonials are still of major importance in the therapeutic strategies used in most endemic regions. However, resistance toward these compounds has recently emerged in areas where the replacement of these drugs is mainly limited by the cost of alternative molecules. In this paper, we reviewed the studies carried out on antimonial resistance in Leishmania. Several common limitations of these works are presented before prevalent approaches to evidence antimonial resistance are related. Afterwards, phenotypic determination of resistance is described, then confronted to clinical outcome. Finally, we detail molecular mechanisms and targets involved in resistance and already identified in vitro within selected mutant strains or in clinical isolates.

In vitro and in vivo behaviour of sympatric Leishmania (V.) braziliensis, L. (V.) peruviana and their hybrids

Leishmania (Viannia) braziliensis is the main cause of highly disfiguring mucocutaneous leishmaniasis (MCL) in South America. The related species L. (V.) peruviana has only been identified in simple cutaneous lesions (CL). Hybrids between L. braziliensis and L. peruviana have been reported although genetic exchange in Leishmania is considered to be rare. Here we compared growth in vitro, adaptive capacity under thermal and oxidative stress and behaviour in a hamster model, of L. braziliensis, L. peruviana, and their putative hybrids. At 24°C, the optimal temperature for in vitro growth, L. braziliensis had the highest growth rate. In in vitro studies hybrid clones presented heterogeneous phenotypes, from slower growth rates, similar to L. peruviana, to higher growth rates, as observed in L. braziliensis. Hamsters infected with hybrid strains, presented the highest parasite densities and aggressive relapses at a later stage of infection. Hybrids generally presented higher plasticity and phenotypic diversity than the putative parental species, with potential eco-epidemiological implications, including an impact on the success of disease control.

A novel A2 allele found in Leishmania (Leishmania) infantum chagasi

Visceral leishmaniasis (VL) is a widely spread zoonotic disease. In Brazil the disease is caused by Leishmania (Leishmania)infantum chagasi. Peridomestic sandflies acquire the etiological agent by feeding on blood of infected reservoir animals, such as dogs or wildlife. The disease is endemic in Brazil and epidemic foci have been reported in densely populated cities all over the country. Many clinical features of Leishmania infection are related to the host-parasite relationship, and many candidate virulence factors in parasites that cause VL have been studied such as A2 genes. The A2 gene was first isolated in 1994 and then in 2005 three new alleles were described in Leishmania (Leishmania) infantum. In the present study we amplified by polymerase chain reaction (PCR) and sequenced the A2 gene from the genome of a clonal population of L. (L.) infantum chagasi VL parasites. The L. (L.) infantum chagasi A2 gene was amplified, cloned, and sequenced in. The amplified fragment showed approximately 90% similarity with another A2 allele amplified in Leishmania (Leishmania) donovani and in L. (L.) infantum described in literature. However, nucleotide translation shows differences in protein amino acid sequence, which may be essential to determine the variability of A2 genes in the species of the L. (L.) donovani complex and represents an additional tool to help understanding the role this gene family may have in establishing virulence and immunity in visceral leishmaniasis. This knowledge is important for the development of more accurate diagnostic tests and effective tools for disease control.

Overexpression of a single Leishmania major gene enhances parasite infectivity in vivo and in vitro

We identified a Leishmania major-specific gene that can partly compensate for the loss of virulence observed for L. major HSP100 null mutants. The gene, encoding a 46 kD protein of unknown function and lineage, also enhances the virulence of wild type L. major upon overexpression. Surprisingly, the approximately sixfold overexpression of this protein also extends the host range of L. major to normally resistant C57BL/6 mice, causing persisting lesions in this strain, even while eliciting a strong cellular immune response. This enhanced virulence in vivo is mirrored in vitro by increased parasite burden inside bone marrow-derived macrophages. The localization of the protein in the macrophage cytoplasm suggests that it may modulate the macrophage effector mechanisms. In summary, our data show that even minor changes of gene expression in L. major may alter the outcome of an infection, regardless of the host's genetic predisposition.

Evaluation of an in vitro and in vivo model for experimental infection with Leishmania (Viannia) braziliensis and L. (V.) peruviana

Leishmania (Viannia) braziliensis and L. (V.) peruviana are two parasite species characterized by a very different pathogenicity in humans despite a high genetic similarity. We hypothesized previously that L. (V.) peruviana would descend from L. (V.) braziliensis and would have acquired its ‘peruviana’ character during the southward colonization and adaptation of the transmission cycle in the Peruvian Andes. In order to have a first appreciation of the differences in virulence between both species, we evaluated an in vitro and in vivo model for experimental infection. A procedure was adapted to enrich culture forms in infective stages and the purified metacyclics were used to infect macrophage cell lines and golden hamsters. The models were tested with 2 representative strains of L. (V.) braziliensis from cutaneous and mucosal origin respectively and 2 representative strains of L. (V.) peruviana from Northern and Southern Peru respectively. Our models were reproducible and sensitive enough to detect phenotypic differences among strains. We showed in vitro as well as in vivo that the L. (V.) braziliensis was more infective than L. (V.) peruviana. Furthermore, we found that in vitro infectivity patterns of the 4 strains analysed, were in agreement with the geographical structuring of parasite populations demonstrated in our previous studies. Further work is needed to confirm our results with more strains of different geographical origin and their specific clinical outcome. However, our data open new perspectives for understanding the process of speciation in Leishmania and its implications in terms of pathogenicity.

Leishmania and the leishmaniases: a parasite genetic update and advances in taxonomy, epidemiology and pathogenicity in humans

Leishmaniases remain a major public health problem today despite the vast amount of research conducted on Leishmania pathogens. The biological model is genetically and ecologically complex. This paper explores the advances in Leishmania genetics and reviews population structure, taxonomy, epidemiology and pathogenicity. Current knowledge of Leishmania genetics is placed in the context of natural populations. Various studies have described a clonal structure for Leishmania but recombination, pseudo-recombination and other genetic processes have also been reported. The impact of these different models on epidemiology and the medical aspects of leishmaniases is considered from an evolutionary point of view. The role of these parasites in the expression of pathogenicity in humans is also explored. It is important to ascertain whether genetic variability of the parasites is related to the different clinical expressions of leishmaniasis. The review aims to put current knowledge of Leishmania and the leishmaniases in perspective and to underline priority questions which 'leishmaniacs' must answer in various domains: epidemiology, population genetics, taxonomy and pathogenicity. It concludes by presenting a number of feasible ways of responding to these questions.

Functional paradox in host–pathogen interaction dictates the fate of parasites

The interactions between the protozoan parasite Leishmania and host macrophages are complex and involve several paradoxical functions that are meant for protection of the host but exploited by the parasite for its survival. The initial interaction of the parasite surface molecules with the host-cell receptors plays a major role in the final outcome of the disease state. While the interactions between macrophages and a virulent strain of Leishmania trigger a cascade of cell-signaling events leading to immunosuppression, the interaction with an avirulent strain triggers host-protective immune effector functions. Thus, an incisive study on Leishmania–macrophage interactions reveals functional paradoxes that highlight the concept of ‘relativity in parasite virulence’. Using Leishmania infection as a model, we propose that virulence of a pathogen and the resistance (or susceptibility) of a host to the pathogen are relative properties that equate to combinatorial functions of several sets of molecular processes.

Leishmania infantum: Mixed T-helper-1/T-helper-2 immune response in experimentally infected BALB/c mice

The main goal of the present study was to characterise the course of infection and immunological responses developed by Leishmania infantum infected BALB/c mice. Parasite load was determined by Real-time TaqMan PCR while cytokine and Immunoglobulin G (IgG) production were assessed by ELISA. Leishmania DNA was detected in spleen and liver as soon as day 1 post-inoculation (pi) and the parasitism was sustained until the end of the experiment. The cytokine kinetics in spleen and liver was generally associated with the oscillations of parasite load. Overall, it was not observed a distinct Th1 or Th2 pattern of cytokine production during the time of experiment. The infected mice developed a mixed immune response, with concomitant production of IFN-gamma, IL-4 and IL-10, both in spleen and liver, and both IgG isotypes. However, our results suggest that, compared to liver, the spleen is more susceptible to L. infantum infection.

Efficacy of orally administered 2-substituted quinolines in experimental murine cutaneous and visceral leishmaniases

We report in this study the in vivo efficacy of nine 2-substituted quinolines on the Leishmania amazonensis cutaneous infection murine model and on the Leishmania infantum and Leishmania donovani visceral infection murine models. In the case of the L. amazonensis model, quinolines were administered orally at 25 mg/kg twice daily for 15 days. Quinolines 1, 2, 3, and 7 reduced by 80 to 90% the parasite burdens in the lesion, whereas N-methylglucamine antimoniate (Glucantime), administered by subcutaneous injections at 100 mg [28 mg Sb(V)] per kg of body weight daily, reduced the parasite burdens by 98%. In visceral leishmaniasis due to L. infantum, mice treated orally at 25 mg/kg daily for 10 days with quinolines 1, 4, 5, and 6 showed a significant reduction of parasite burdens in the liver and spleen. These quinolines were significantly more effective than meglumine antimoniate to reduce the parasite burden in both the liver and spleen. Also, the oral in vivo activity of three quinolines (quinolines 4, 5, and 2-n-propylquinoline) were determined against L. donovani (LV 9) at 12.5 and 25 mg/kg for 10 days. Their activity was compared with that of miltefosine at 7.5 mg/kg. Miltefosine, 2-n-propylquinoline, and quinoline 5 at 12.5 mg/kg significantly reduced the parasite burdens in the liver by 72, 66, and 61%, respectively. From the present study, quinoline 5 is the most promising compound against both cutaneous and visceral leishmaniasis. The double antileishmanial and antiviral activities of these compounds suggest that this series could be a potential treatment for coinfection of Leishmania-human immunodeficiency virus.

Leishmania chagasi/infantum: further investigations on Leishmania tropisms in atypical cutaneous and visceral leishmaniasis foci in Central America

In Central America, apparently genetically identical Leishmania chagasi/infantum parasites cause cutaneous (CL) and visceral leishmaniasis (VL), the latter being more frequent in young children. The present study investigated if there were pathology-related differences in virulence between Honduran CL and VL strains using Mediterranean L. infantum strains as a reference. Macrophage infectivity and serum sensitivity, properties thought to be associated with virulence, were similar between CL and VL strains from both regions. Attention focused on the genome organisation of genes for two candidate virulence factors: Leishmania mitogen activated protein kinase (LMPK) and cysteine proteinase b (Cpb). Interestingly, the Mediterranean strains exhibited restriction enzyme polymorphisms associated with tropism for both LMPK and Cpb genes whereas no differences were observed for the Honduran strains. We also report relative genetic homogeneity of the Honduran strains as compared to the Mediterranean strains and discuss it in terms of the probable origin for the Central American L. chagasi/infantum.

A2 gene of Old World cutaneous Leishmania is a single highly conserved functional gene

BACKGROUND

Leishmaniases are among the most proteiform parasitic infections in humans ranging from unapparent to cutaneous, mucocutaneous or visceral diseases. The various clinical issues depend on complex and still poorly understood mechanisms where both host and parasite factors are interacting. Among the candidate factors of parasite virulence are the A2 genes, a family of multiple genes that are developmentally expressed in species of the Leishmania donovani group responsible for visceral diseases (VL). By contrast, in L. major determining cutaneous infections (CL) we showed that A2 genes are present in a truncated form only. Furthermore, the A2 genomic sequences of L. major were considered subsequently to represent non-expressed pseudogenes 1. Consequently, it was suggested that the structural and functional properties of A2 genes could play a role in the differential tropism of CL and VL leishmanias. On this basis, it was of importance to determine whether the observed structural/functional particularities of the L. major A2 genes were shared by other CL Leishmania, therefore representing a proper characteristic of CL A2 genes as opposed to those of VL isolates.

METHODS

In the present study we amplified by PCR and sequenced the A2 genes from genomic DNA and from clonal libraries of the four Old World CL species comparatively to a clonal population of L. infantum VL parasites. Using RT-PCR we also amplified and sequenced A2 mRNA transcripts from L. major.

RESULTS

A unique A2 sequence was identified in Old World cutaneous Leishmania by sequencing. The shared sequence was highly conserved among the various CL strains and species analysed, showing a single polymorphism C/G at position 58. The CL A2 gene was found to be functionally transcribed at both parasite stages.

CONCLUSION

The present study shows that cutaneous strains of leishmania share a conserved functional A2 gene. As opposed to the multiple A2 genes described in VL isolates, the CL A2 gene is unique, lacking most of the nucleotide repeats that constitute the variable region at the 5'end of the VL A2 sequences. As the variable region of the VL A2 gene has been shown to correspond to a portion of the protein which is highly immunogenic, the present results support the hypothesis of a possible role of the A2 gene in the differential tropism of CL and VL leishmania parasites.

Recent developments in leishmaniasis

PURPOSE OF REVIEW

The leishmaniases, caused by protozoan parasites of the genus Leishmania, are a significant health problem in many regions of the world. This review highlights the recent advances in the study of leishmaniasis related to parasite biology, disease pathogenesis, clinical evaluation and treatment, and prevention.

RECENT FINDINGS

Genetic heterogeneity and clonal diversity is common among Leishmania strains. Gene knockout, overexpression, and re-introduction studies have identified a number of genes that play a role in parasite virulence. Surprisingly, the importance of the surface lipophosphoglycan in parasite virulence appears to differ among Leishmania spp. Studies in experimental animal models have further defined the roles of CD4 and CD8 T cells, IL-4, IL-10, and IL-12 in the control, maintenance, or progression of disease. The effect of Leishmania on dendritic cells and macrophage effector function has also been an important area of investigation. A number of new vaccine candidates have been identified through experimental animal studies. Clinical studies of leishmaniasis have focused on the host determinants of disease (most notably HIV co-infection), serological and DNA-based diagnostic assays, and treatment. Antimony-resistant cases of cutaneous and visceral leishmaniasis have become more common; liposomal amphotericin and oral miltefosine are promising alternative therapies.

SUMMARY

Significant advances have been made in the areas of pathogenesis, host defence, and treatment of leishmaniasis. A number of new vaccine candidates and potential targets of drug therapy have been identified, but progress from preclinical studies to clinical trials has been slow. Translational research, built upon the solid foundation of existing and ongoing basic investigation, is a high priority.

Microplate method for obtaining Leishmania clonal populations

The various clinical expressions observed in human leishmaniases result from complex host-parasite relationships in which the biodiversity of the parasite is a determining factor. Because Leishmania strains isolated from humans are composed of heterogeneous populations, it is crucial to use clonal lineages for studies on the characterization of these parasites. Presently, techniques used for cloning Leishmania spp. parasites are time-consuming and show poor efficiency. Here, a method developed in 96-well microplates is described, which allows one to rapidly obtain numerous clones of Leishmania in the most versatile and efficient way. The technique may be useful for cloning various protozoa as well as Leishmania spp.

In vitro susceptibility to pentavalent antimony in Leishmania infantum strains is not modified during in vitro or in vivo passages but is modified after host treatment with meglumine antimoniate

BACKGROUND

Leishmaniasis is a common parasitic disease in Southern Europe, caused by Leishmania infantum. The failures of current treatment with pentavalent antimonials are partially attributable to the emergence of antimony-resistant Leishmania strains. This study analyses the in vitro susceptibility to pentavalent antimony of intracellular amastigotes from a range of L. infantum strains, derived from the same infected animal, during in vitro and in vivo passages and after host treatment with meglumine antimoniate.

RESULTS

SbV-IC50 values for strains from two distinct isolates from the same host and one stock after two years of culture in NNN medium and posterior passage to hamster were similar (5.0 +/- 0.2; 4.9 +/- 0.2 and 4.4 +/- 0.1 mgSbV/L, respectively). In contrast, a significant difference (P < 0.01, t test) was observed between the mean SbV-IC50 values in the stocks obtained before and after treatment of hosts with meglumine antimoniate (4.7 +/- 0.4 mgSbV/L vs. 7.7 +/- 1.5 mgSbV/L). Drug-resistance after drug pressure in experimentally infected dogs increased over repeated drug administration (6.4 +/- 0.5 mgSbV/L after first treatment vs. 8.6 +/- 1.4 mgSbV/L after the second) (P < 0.01, t test).

CONCLUSIONS

These results confirm previous observations on strains from Leishmania/HIV co-infected patients and indicate the effect of the increasing use of antimony derivatives for treatment of canine leishmaniasis in endemic areas on the emergence of Leishmania antimony-resistant strains.