Leishmune vaccine blocks the transmission of canine visceral leishmaniasis: absence of Leishmania parasites in blood, skin and lymph nodes of vaccinated exposed dogs

A state-of-the-art methodology for high-throughput in silico vaccine discovery against protozoan parasites and exemplified with discovered candidates for Toxoplasma gondii

Vaccine discovery against eukaryotic parasites is not trivial as highlighted by the limited number of known vaccines compared to the number of protozoal diseases that need one. Only three of 17 priority diseases have commercial vaccines. Live and attenuated vaccines have proved to be more effective than subunit vaccines but adversely pose more unacceptable risks. One promising approach for subunit vaccines is in silico vaccine discovery, which predicts protein vaccine candidates given thousands of target organism protein sequences. This approach, nonetheless, is an overarching concept with no standardised guidebook on implementation. No known subunit vaccines against protozoan parasites exist as a result of this approach, and consequently none to emulate. The study goal was to combine current in silico discovery knowledge specific to protozoan parasites and develop a workflow representing a state-of-the-art approach. This approach reflectively integrates a parasite's biology, a host's immune system defences, and importantly, bioinformatics programs needed to predict vaccine candidates. To demonstrate the workflow effectiveness, every Toxoplasma gondii protein was ranked in its capacity to provide long-term protective immunity. Although testing in animal models is required to validate these predictions, most of the top ranked candidates are supported by publications reinforcing our confidence in the approach.

Type II DNA Topoisomerases in trypanosomatid and apicomplexan parasites

Diseases caused by trypanosomatid parasites have no commercially available vaccines for human application. Treatment modalities completely rely on chemotherapeutics strategies that often exhibit clinical drawbacks, like host toxicity, side effects and treatment failure for drug resistance. These, in many instances, are costly, making them unaffordable for certain groups of beneficiaries. To find reasonable solutions, researchers are attempting to identify and validate new drug targets that would offer parasite specificity. DNA topoisomerases in parasites present a consolidated class of drug targets due to their multiple structural and functional differences with host homologs. Type II DNA topoisomerases in these parasites, in particular, have been attracting interest of scientific community attributable to their pivotal role in the replication of the atypical DNA. In this article, we present a detailed review of structural and functional features of type II DNA topoisomerases of clinically-relevant trypanosomatid and apicomplexan parasites. Also, we provide up-to-date information on different molecules that target these enzymes. Altogether, the review will largely help in understanding the rationale for exploiting type II DNA topoisomerases in these groups of parasites as drug targets.

Vaccination in Leishmaniasis: A Review Article

Leishmaniasis is caused by protozoan Leishmania parasites that are transmitted through female sandfly bites. The disease is predominantly endemic to the tropics and semi-tropics and has been reported in more than 98 countries. Due to the side effects of anti-Leishmania drugs and the emergence of drug-resistant isolates, there is currently no encouraging prospect of introducing an effective therapy for the disease. Hence, it seems that the key to disease control management is the introduction of an effective vaccine, particularly against its cutaneous form. Advances in understanding underlying immune mechanisms are feasibale using a variety of candidate antigens, including attenuated live parasites, crude antigens, pure or recombinant Leishmania proteins, Leishmania genes encoding protective proteins, as well as immune system activators from the saliva of parasite vectors. However, there is still no vaccine against different types of human leishmaniasis. In this study, we review the works conducted or being performed in this field.

FML/QuilA-Vaccinated Dogs Naturally Infected with Leishmania infantum: Serum Cytokines, Clinicopathological Profile, and Parasitological Parameters

Dogs are the main reservoir of Leishmania infantum in endemic regions. Canine leishmaniasis, caused by L. infantum, can progress to a chronic disease resulting in death. Vaccines have been developed with a certain degree of success. The pathogenesis of this disease is not completely understood, especially in previously vaccinated dogs. We herein described clinical data, parasite load, serum levels of cytokines, and the reservoir potential in vdogs vaccinated with the fucose-mannose ligand (FML)/QuilA saponin vaccine (Leishmune™) naturally infected (Vi) and compared to vaccinated not infected dogs (Vn). Thirty-four dogs from private owners were divided into two groups: vaccinated/infected and vaccinated/uninfected. Clinical evaluation, hematological and biochemical parameters, and serum levels of cytokines were measured by conventional methods. The parasite burden in the bone marrow was measured by quantitative real-time PCR, and the transmissibility of parasites to sand flies was assessed by xenodiagnosis. Clinical, biochemical, and hematological parameters of vaccinated infected dogs were mostly normal. Vi dogs developed mild disease with low clinical scores. Serum levels of IL-10 were higher in Vi dogs, and a strong correlation was observed in IL-4 levels and the A/G ratio in Vi dogs. These results suggest a role of TH2 response in Vi dogs, although more data is needed to better understand the disease in vaccinated dogs.

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.

The Delay in the Licensing of Protozoal Vaccines: A Comparative History

Although viruses and bacteria have been known as agents of diseases since 1546, 250 years went by until the first vaccines against these pathogens were developed (1796 and 1800s). In contrast, Malaria, which is a protozoan-neglected disease, has been known since the 5th century BCE and, despite 2,500 years having passed since then, no human vaccine has yet been licensed for Malaria. Additionally, no modern human vaccine is currently licensed against Visceral or Cutaneous leishmaniasis. Vaccination against Malaria evolved from the inoculation of irradiated sporozoites through the bite of Anopheles mosquitoes in 1930's, which failed to give protection, to the use of controlled human Malaria infection (CHMI) provoked by live sporozoites of Plasmodium falciparum and curtailed with specific chemotherapy since 1940's. Although the use of CHMI for vaccination was relatively efficacious, it has some ethical limitations and was substituted by the use of injected recombinant vaccines expressing the main antigens of the parasite cycle, starting in 1980. Pre-erythrocytic (PEV), Blood stage (BSV), transmission-blocking (TBV), antitoxic (AT), and pregnancy-associated Malaria vaccines are under development. Currently, the RTS,S-PEV vaccine, based on the circumsporozoite protein, is the only one that has arrived at the Phase III trial stage. The “R” stands for the central repeat region of Plasmodium (P.) falciparum circumsporozoite protein (CSP); the “T” for the T-cell epitopes of the CSP; and the “S” for hepatitis B surface antigen (HBsAg). In Africa, this latter vaccine achieved only 36.7% vaccine efficacy (VE) in 5–7 years old children and was associated with an increase in clinical cases in one assay. Therefore, in spite of 35 years of research, there is no currently licensed vaccine against Malaria. In contrast, more progress has been achieved regarding prevention of leishmaniasis by vaccine, which also started with the use of live vaccines. For ethical reasons, these were substituted by second-generation subunit or recombinant DNA and protein vaccines. Currently, there is one live vaccine for humans licensed in Uzbekistan, and four licensed veterinary vaccines against visceral leishmaniasis: Leishmune® (76–80% VE) and CaniLeish® (68.4% VE), which give protection against strong endpoints (severe disease and deaths under natural conditions), and, under less severe endpoints (parasitologically and PCR-positive cases), Leishtec® developed 71.4% VE in a low infective pressure area but only 35.7% VE and transient protection in a high infective pressure area, while Letifend® promoted 72% VE. A human recombinant vaccine based on the Nucleoside hydrolase NH36 of Leishmania (L.) donovani, the main antigen of the Leishmune® vaccine, and the sterol 24-c-methyltransferase (SMT) from L. (L.) infantum has reached the Phase I clinical trial phase but has not yet been licensed against the disease. This review describes the history of vaccine development and is focused on licensed formulations that have been used in preventive medicine. Special attention has been given to the delay in the development and licensing of human vaccines against Protozoan infections, which show high incidence worldwide and still remain severe threats to Public Health.

Commercially approved vaccines for canine leishmaniosis: a review of available data on their safety and efficacy

Canine leishmaniosis is an important vector-borne zoonosis caused mainly by Leishmania infantum. Diagnosis and treatment of affected individuals can be particularly complex, hindering infection control in endemic areas. Methods to prevent canine leishmaniosis include the use of topical insecticides, prophylactic immunotherapy and vaccination. Four vaccines against canine leishmaniosis have been licensed since 2004, two in Brazil (Leishmune®, the production and marketing licence of which was withdrawn in 2014, and Leish-Tec®) and two in Europe (CaniLeish® and LetiFend®). After several years of marketing, doubts remain regarding vaccine efficacy and effectiveness, potential infectiousness of vaccinated and infected animals or the interference of vaccine-induced antibodies in L. infantum serological diagnosis. This review summarises the scientific evidence for each of the vaccines commercially approved for canine leishmaniosis, while discussing possible weaknesses of these studies. Furthermore, it raises the need to address important questions related to vaccination impact in Leishmania-endemic countries and the importance of post-marketing pharmacological surveillance.

Anti-Leishmanial Vaccines: Assumptions, Approaches, and Annulments

Leishmaniasis is a neglected protozoan parasitic disease that occurs in 88 countries but a vaccine is unavailable. Vaccination with live, killed, attenuated (physically or genetically) Leishmania have met with limited success, while peptide-, protein-, or DNA-based vaccines showed promise only in animal models. Here, we critically assess several technical issues in vaccination and expectation of a host-protective immune response. Several studies showed that antigen presentation during priming and triggering of the same cells in infected condition are not comparable. Altered proteolytic processing, antigen presentation, protease-susceptible sites, and intracellular expression of pathogenic proteins during Leishmania infection may vary dominant epitope selection, MHC-II/peptide affinity, and may deter the reactivation of desired antigen-specific T cells generated during priming. The robustness of the memory T cells and their functions remains a concern. Presentation of the antigens by Leishmania-infected macrophages to antigen-specific memory T cells may lead to change in the T cells' functional phenotype or anergy or apoptosis. Although cells may be activated, the peptides generated during infection may be different and cross-reactive to the priming peptides. Such altered peptide ligands may lead to suppression of otherwise active antigen-specific T cells. We critically assess these different immunological issues that led to the non-availability of a vaccine for human use.

Nucleoside Hydrolase NH 36: A Vital Enzyme for the Leishmania Genus in the Development of T-Cell Epitope Cross-Protective Vaccines

NH36 is a vital enzyme of the DNA metabolism and a specific target for anti-Leishmania chemotherapy. We developed second-generation vaccines composed of the FML complex or its main native antigen, the NH36 nucleoside hydrolase of Leishmania (L.) donovani and saponin, and a DNA vaccine containing the NH36 gene. All these vaccines were effective in prophylaxis and treatment of mice and dog visceral leishmaniasis (VL). The FML-saponin vaccine became the first licensed veterinary vaccine against leishmaniasis (Leishmune®) which reduced the incidence of human and canine VL in endemic areas. The NH36, DNA or recombinant protein vaccines induced a Th1 CD4+IFN-γ+ mediated protection in mice. Efficacy against VL was mediated by a CD4+TNF-α T lymphocyte response against the NH36-F3 domain, while against tegumentary leishmaniasis (TL) a CD8+ T lymphocyte response to F1 was also required. These domains were 36-41 % more protective than NH36, and a recombinant F1F3 chimera was 21% stronger than the domains, promoting a 99.8% reduction of the parasite load. We also identified the most immunogenic NH36 domains and epitopes for PBMC of active human VL, cured or asymptomatic and DTH+ patients. Currently, the NH36 subunit recombinant vaccine is turning into a multi-epitope T cell synthetic vaccine against VL and TL.

NH36 and F3 Antigen-Primed Dendritic Cells Show Preserved Migrating Capabilities and CCR7 Expression and F3 Is Effective in Immunotherapy of Visceral Leishmaniasis

Physical contact between dendritic cells (DCs) and T cell lymphocytes is necessary to trigger the immune cell response. CCL19 and CCL21 chemokines bind to the CCR7 receptor of mature DCs, and of T cells and regulate DCs migration to the white pulp (wp) of the spleen, where they encounter lymphocytes. In visceral leishmaniasis (VL), cellular immunosuppression is mediated by impaired DC migration due to the decreased chemokine secretion by endothelium and to the reduced DCs CCR7 expression. The Leishmania (L.) donovani nucleoside hydrolase NH36 and its C-terminal domain, the F3 peptide are prominent antigens in the generation of preventive immunity to VL. We assessed whether these vaccines could prevent the migrating defect of DCs by restoring the expression of CCR7 receptors. C57Bl6 mice were vaccinated with NH36 and F3 and challenged with L. (L.) infantum chagasi. The F3 vaccine induced a 100% of survival and a long-lasting immune protection with an earlier CD4+Th1 response, with secretion of higher IFN-γ and TNF-α/IL-10 ratios, and higher frequencies of CD4+ T cells secreting IL-2+, TNF-α+, or IFN-γ+, or a combination of two or the three cytokines (IL-2+TNF-α+IFN-γ+). The CD8+ T cell response was promoted earlier by the NH36-vaccine, and later by the F3-vaccine. Maximal number of F3-primed DCs migrated in vitro in response to CCL19 and showed a high expression of CCR7 receptors (26.06%). Anti-CCR7 antibody treatment inhibited DCs migration in vitro (90%) and increased parasite load in vivo. When transferred into 28-day-infected mice, only 8% of DCs from infected, 59% of DCs from NH36-vaccinated, and 84% of DCs from F3-vaccinated mice migrated to the wp. Consequently, immunotherapy of infected mice with F3-primed DCs only, promoted increases in corporal weight and reductions of spleen and liver parasite loads and relative weights. Our findings indicate that vaccination with F3-vaccine preserves the maturation, migration properties and CCR7 expression of DCs, which are essential processes for the generation of cell-mediated immunity. The F3 vaccine is more potent in reversing the migration defect that occurs in VL and, therefore, more efficient in immunotherapy of VL.

Liposomal Elongation Factor-1α Triggers Effector CD4 and CD8 T Cells for Induction of Long-Lasting Protective Immunity against Visceral Leishmaniasis

Despite advances, identification and formulation of safe and effective vaccine for long-lasting protection against leishmaniasis is still inadequate. In this study, we have identified a novel antigen, leishmanial elongation factor-1α (EF1-α), as an immunodominant component of solubilized leishmanial membrane antigens that reacts with visceral leishmaniasis (VL) sera and induces cellular proliferative and cytokine response in PBMCs of cured VL subjects. Leishmanial EF1-α is a 50 kDa antigen that plays a crucial role in pathogen survival by regulating oxidative burst in the host phagocytes. Previously, immunodominant truncated forms of EF1-α from different species of Leishmania have been reported. Formulation of the L. donovani 36 kDa truncated as well as the cloned recombinant EF1-α in cationic liposomes induce strong resistance to parasitic burden in liver and spleen of BALB/c mice through induction of DTH and a IL-10 and TGF-β suppressed mixed Th1/Th2 cytokine responses. Multiparametric analysis of splenocytes for generation of antigen-specific IFN-γ, IL2, and TNF-α producing lymphocytes indicate that cationic liposome facilitates expansion of both CD4⁺ as well as CD8⁺ memory and effector T cells. Liposomal EF1-α is a novel and potent vaccine formulation against VL that imparts long-term protective responses. Moreover, the flexibility of this formulation opens up the scope to combine additional adjuvants and epitope selected antigens for use in other disease forms also.

Leishmania donovani Nucleoside Hydrolase (NH36) Domains Induce T-Cell Cytokine Responses in Human Visceral Leishmaniasis

Development of immunoprotection against visceral leishmaniasis (VL) focused on the identification of antigens capable of inducing a Th1 immune response. Alternatively, antigens targeting the CD8 and T-regulatory responses are also relevant in VL pathogenesis and worthy of being included in a preventive human vaccine. We assessed in active and cured patients and VL asymptomatic subjects the clinical signs and cytokine responses to the Leishmania donovani nucleoside hydrolase NH36 antigen and its N-(F1), central (F2) and C-terminal (F3) domains. As markers of VL resistance, the F2 induced the highest levels of IFN-γ, IL-1β, and TNF-α and, together with F1, the strongest secretion of IL-17, IL-6, and IL-10 in DTH+ and cured subjects. F2 also promoted the highest frequencies of CD3+CD4+IL-2+TNF-α-IFN-γ-, CD3+CD4+IL-2+TNF-α+IFN-γ-, CD3+CD4+IL-2+TNF-α-IFN-γ+, and CD3+CD4+IL-2+TNF-α+IFN-γ+ T cells in cured and asymptomatic subjects. Consistent with this, the IFN-γ increase was correlated with decreased spleen (R = -0.428, P = 0.05) and liver sizes (R = -0.428, P = 0.05) and with increased hematocrit counts (R = 0.532, P = 0.015) in response to F1 domain, and with increased hematocrit (R = 0.512, P 0.02) and hemoglobin counts (R = 0.434, P = 0.05) in response to F2. Additionally, IL-17 increases were associated with decreased spleen and liver sizes in response to F1 (R = -0.595, P = 0.005) and F2 (R = -0.462, P = 0.04). Conversely, F1 and F3 increased the CD3+CD8+IL-2+TNF-α-IFN-γ-, CD3+CD8+IL-2+TNF-α+IFN-γ-, and CD3+CD8+IL-2+TNF-α+IFN-γ+ T cell frequencies of VL patients correlated with increased spleen and liver sizes and decreased hemoglobin and hematocrit values. Therefore, cure and acquired resistance to VL correlate with the CD4+-Th1 and Th-17 T-cell responses to F2 and F1 domains. Clinical VL outcomes, by contrast, correlate with CD8+ T-cell responses against F3 and F1, potentially involved in control of the early infection. The in silico-predicted NH36 epitopes are conserved and bind to many HL-DR and HLA and B allotypes. No human vaccine against Leishmania is available thus far. In this investigation, we identified the NH36 domains and epitopes that induce CD4+ and CD8+ T cell responses, which could be used to potentiate a human universal T-epitope vaccine against leishmaniasis.

The importance of nucleoside hydrolase enzyme (NH) in studies to treatment of Leishmania: A review

Leishmania is a genus of trypanosomes, which are responsible for leishmaniasis disease, a major trypanosome infection in humans. In recent years, published studies have shown that the search for new drugs for Leishmania treatments has intensified. Through technique modeling it has been possible to develop new compounds, which act as nucleoside hydrolase (NH) inhibitors. The effect of these enzymes is the hydrolysis of certain RNA nucleotides, which include uridine and inosine, necessary for the protozoa to transform certain nucleosides obtained from infected individuals into nucleobases for the preparation of their DNA. The obtention of NH inhibitors is very important to eliminate leishmaniasis disease in infected individuals. The aim of this study is to discuss the research and development of new agents for the treatment of Leishmania, and to stimulate the formulation of new NH inhibitors.

Progress in the Mathematical Modelling of Visceral Leishmaniasis

The leishmaniases comprise a complex of diseases characterized by clinical outcomes that range from self-limiting to chronic, and disfiguring and stigmatizing to life threatening. Diagnostic methods, treatments, and vector and reservoir control options exist, but deciding the most effective interventions requires a quantitative understanding of the population level infection and disease dynamics. The effectiveness of any set of interventions has to be determined within the context of operational conditions, including economic and political commitment. Mathematical models are the best available tools for studying quantitative systems crossing disciplinary spheres (biology, medicine, economics) within environmental and societal constraints. In 2005, the World Health Assembly and government health ministers of India, Nepal, and Bangladesh signed a Memorandum of Understanding to eliminate the life threatening form of leishmaniasis, visceral leishmaniasis (VL), on the Indian subcontinent by 2015 through a combination of early case detection, improved treatments, and vector control. The elimination target is <1 case/10,000 population at the district or subdistrict level compared to the current 20/10,000 in the regions of highest transmission. Towards this goal, this chapter focuses on mathematical models of VL, and the biology driving those models, to enable realistic predictions of the best combination of interventions. Several key issues will be discussed which have affected previous modelling of VL and the direction future modelling may take. Current understanding of the natural history of disease, immunity (and loss of immunity), and stages of infection and their durations are considered particularly for humans, and also for dogs. Asymptomatic and clinical infection are discussed in the context of their relative roles in Leishmania transmission, as well as key components of the parasite-sandfly-vector interaction and intervention strategies including diagnosis, treatment and vector control. Gaps in current biological knowledge and potential avenues to improve model structures and mathematical predictions are identified. Underpinning the marriage between biology and mathematical modelling, the content of this chapter represents the first step towards developing the next generation of models for VL.

Current status on prevention and treatment of canine leishmaniasis

Canine leishmaniasis (CanL) is a parasite-borne disease mainly induced by Leishmania infantum in the Old World and Leishmania chagasi (infantum) in the New World. CanL is a zoonosis transmitted by the bite of infected Phlebotominae flies that act as vectors. CanL is a very serious disease that usually produces death when remains untreated and can be a focus of transmission to other dogs or humans. Infected dogs and other domestic and wild animals act as reservoirs and are a real threat to uninfected/healthy dogs and humans in endemic areas where the sand flies are present. Prevention of new infections in dogs can help to stop the current increase of the disease in humans, reinforcing the concept of "One Health" approach. The management of CanL is being performed using prophylactic measures in healthy dogs - insecticides impregnated in collars or immunostimulants applied by spot-on devices - and chemotherapy in animals that suffer from the disease. Antimonials as first-line monotherapy have proven efficacy in reducing most of the clinical signs of CanL, but they need to be administered during several days, and no complete parasite clearance is achieved, favouring the presence of relapses among treated dogs. Therefore, new drugs, such as miltefosine, or combinations of this drug or antimonials with allopurinol are in the pipeline of clinical treatment of CanL. Recently, there has been an emergence of protective - prophylactic - and curative - autogenous vaccines - immunotherapy tools to face CanL, whose results are still under study. This review highlights the current use of preventive and eradicative weapons to fight against this disease, which is a scourge for dogs and a continuous threat to human beings.

Effects of specific antisera targeting peritrophic matrix-associated proteins in the sand fly vector Phlebotomus papatasi

In many hematophagous insects, the peritrophic matrix (PM) is formed soon after a blood meal (PBM) to compartmentalize the food bolus. The PM is an important component of vector competence, functioning as a barrier to the development of many pathogens including parasites of the genus Leishmania transmitted by sand flies. PM morphology and permeability are associated with the proteins that are part of the PM scaffolding, including several peritrophins, and chitin fibers. Here, we assessed the effects of specific antisera targeting proteins thought to be an integral part of the PM scaffolding and its process of maturation and degradation. Phlebotomus papatasi sand flies were fed with red blood cells reconstituted with antisera targeting the chitinase PpChit1, and the peritrophin PpPer2. Sand fly midguts were dissected at different time points and processed for light microscopy (LM), confocal and transmission electron (TEM) microscopies (24, 42-46, 48 and 72h PBM), scanning electron (SEM) (48h PBM) and atomic force (AFM) (30h PBM) microscopies. TEM and WGA-FITC staining indicate PM degradation was significantly delayed following feeding of flies on anti-PpChit1. AFM analysis at 30h PBM point to an increase in roughness' amplitude of the PM of flies that fed on either anti-PpChit1 or anti-PpPer2. Collective, our data suggest that antibodies targeting PM-associated proteins affects the kinetics of PM maturation, delaying its degradation and disruption and are potential targets on transmission-blocking vaccines strategies.

Recombinant Forms of Leishmania amazonensis Excreted/Secreted Promastigote Surface Antigen (PSA) Induce Protective Immune Responses in Dogs

Preventive vaccination is a highly promising strategy for interrupting leishmaniasis transmission that can, additionally, contribute to elimination. A vaccine formulation based on naturally excreted secreted (ES) antigens was prepared from L. infantum promastigote culture supernatant. This vaccine achieved successful results in Phase III trials and was licensed and marketed as CaniLeish. We recently showed that newly identified ES promastigote surface antigen (PSA), from both viable promastigotes and axenically-grown amastigotes, represented the major constituent and the highly immunogenic antigen of L. infantum and L. amazonensis ES products. We report here that three immunizations with either the recombinant ES LaPSA-38S (rPSA) or its carboxy terminal part LaPSA-12S (Cter-rPSA), combined with QA-21 as adjuvant, confer high levels of protection in naive L. infantum-infected Beagle dogs, as checked by bone marrow parasite absence in respectively 78.8% and 80% of vaccinated dogs at 6 months post-challenge. The parasite burden in infected vaccinated dogs was significantly reduced compared to placebo group, as measured by q-PCR. Moreover, our results reveal humoral and cellular immune response clear-cut differences between vaccinated and control dogs. An early increase in specific IgG2 antibodies was observed in rPSA/QA-21- and Cter-rPSA/QA-21-immunized dogs only. They were found functionally active in vitro and were highly correlated with vaccine protection. In vaccinated protected dogs, IFN-γ and NO productions, as well as anti-leishmanial macrophage activity, were increased. These data strongly suggest that ES PSA or its carboxy-terminal part, in recombinant forms, induce protection in a canine model of zoonotic visceral leishmaniasis by inducing a Th1-dominant immune response and an appropriate specific antibody response. These data suggest that they could be considered as important active components in vaccine candidates.

Visceral leishmaniasis (VL), a potentially fatal disease caused by L. infantum, represents perfectly the need for a “One Health” approach for disease control, since it affects both humans and dogs, with similar clinical outcome and T-cell mediated immunity commitment. The dog vaccine development is highly required as our present resources for VL treatment and control have a limited effectiveness. It would represent the most convenient and efficient control way to decrease the dog-sandfly-dog transmission cycle, essential for human incidence reduction. The results indicate that recombinant forms of soluble promastigote surface antigen (PSA) are very promising effective vaccine candidates against canine VL. The elicited immune responses effectively reduced parasite load in in vitro pre-infected macrophages and in experimentally infected dogs. Through this approach, we aim to reduce the number of infected animals developing progressive infections thereby positively influencing human public health.

Immunogenicity in dogs and protection against visceral leishmaniasis induced by a 14kDa Leishmania infantum recombinant polypeptide

In areas were human visceral leishmaniasis (VL) is endemic, the domestic dog is the main parasite reservoir in the infectious cycle of Leishmania infantum. Development of prophylactic strategies to lower the parasite burden in dogs would reduce sand fly transmission thus lowering the incidence of zoonotic VL. Here we demonstrate that vaccination of dogs with a recombinant 14kDa polypeptide of L. infantum nuclear transport factor 2 (Li-ntf2) mixed with adjuvant BpMPLA-SE resulted in the production of specific anti-Li-ntf2 IgG antibodies as well as IFN-γ release by the animals' peripheral blood mononuclear cells stimulated with the antigen. In addition, immunization with this single and small 14kDa poplypeptide resulted in protracted progression of the infection of the animals after challenging with a high dose of virulent L. infantum. Five months after challenge the parasite load was lower in the bone marrow of immunized dogs compared to non-immunized animals. The antibody response to K39, a marker of active VL, at ten months after challenge was strong and significantly higher in the control dogs than in vaccinated animals. At the study termination vaccinated animals showed significantly more liver granulomas and lymphoid hyperplasia than non-vaccinated animals, which are both histological markers of resistance to infection. Together, these results indicate that the 14kDa polypeptide is an attractive protective molecule that can be easily incorporated in a leishmanial polyprotein vaccine candidate to augment/complement the overall protective efficacy of the final product.

Efficacy of Recombinant Canine Distemper Virus Expressing Leishmania Antigen against Leishmania Challenge in Dogs

Canine distemper virus (CDV) vaccination confers long-term protection against CDV reinfection. To investigate the utility of CDV as a polyvalent vaccine vector for Leishmania, we generated recombinant CDVs, based on an avirulent Yanaka strain, that expressed Leishmania antigens: LACK, TSA, or LmSTI1 (rCDV-LACK, rCDV-TSA, and rCDV-LmSTI1, respectively). Dogs immunized with rCDV-LACK were protected against challenge with lethal doses of virulent CDV, in the same way as the parental Yanaka strain. To evaluate the protective effects of the recombinant CDVs against cutaneous leishmaniasis in dogs, dogs were immunized with one recombinant CDV or a cocktail of three recombinant CDVs, before intradermal challenge (in the ears) with infective-stage promastigotes of Leishmania major. Unvaccinated dogs showed increased nodules with ulcer formation after 3 weeks, whereas dogs immunized with rCDV-LACK showed markedly smaller nodules without ulceration. Although the rCDV-TSA- and rCDV-LmSTI1-immunized dogs showed little protection against L. major, the cocktail of three recombinant CDVs more effectively suppressed the progression of nodule formation than immunization with rCDV-LACK alone. These results indicate that recombinant CDV is suitable for use as a polyvalent live attenuated vaccine for protection against both CDV and L. major infections in dogs.

Vaccination with Leishmania infantum acidic ribosomal P0 but not with nucleosomal histones proteins controls Leishmania infantum infection in hamsters

Background

Several intracellular Leishmania antigens have been identified in order to find a potential vaccine capable of conferring long lasting protection against Leishmania infection. Histones and Acid Ribosomal proteins are already known to induce an effective immune response and have successfully been tested in the cutaneous leishmaniasis mouse model. Here, we investigate the protective ability of L. infantum nucleosomal histones (HIS) and ribosomal acidic protein P0 (LiP0) against L. infantum infection in the hamster model of visceral leishmaniasis using two different strategies: homologous (plasmid DNA only) or heterologous immunization (plasmid DNA plus recombinant protein and adjuvant).

Methodology/Principal Findings

Immunization with both antigens using the heterologous strategy presented a high antibody production level while the homologous strategy immunized group showed predominantly a cellular immune response with parasite load reduction. The pcDNA-LiP0 immunized group showed increased expression ratio of IFN-γ/IL-10 and IFN-γ/TGF-β in the lymph nodes before challenge. Two months after infection hamsters immunized with the empty plasmid presented a pro-inflammatory immune response in the early stages of infection with increased expression ratio of IFN-γ/IL-10 and IFN-γ/TGF-β, whereas hamsters immunized with pcDNA-HIS presented an increase only in the ratio IFN-γ/ TGF-β. On the other hand, hamsters immunized with LiP0 did not present any increase in the IFN-γ/TGF-β and IFN-γ/IL-10 ratio independently of the immunization strategy used. Conversely, five months after infection, hamsters immunized with HIS maintained a pro-inflammatory immune response (ratio IFN-γ/ IL-10) while pcDNA-LiP0 immunized hamsters continued showing a balanced cytokine profile of pro and anti-inflammatory cytokines. Moreover we observed a significant reduction in parasite load in the spleen, liver and lymph node in this group compared with controls.

Conclusions/Significance

Our results suggest that vaccination with L. infantum LiP0 antigen administered in a DNA formulation could be considered a potential component in a vaccine formulation against visceral leishmaniasis.

Visceral leishmaniasis caused by Leishmania infantum is the most severe form of leishmaniasis. The disease is fatal if not treated and there is no vaccine available for human use. In the search for potential antigens, the protective ability of conserved parasite protein families such as L. infantum histones (HIS) and acidic ribosomal (LiP0) antigens were successfully tested in the mouse model of cutaneous leishmaniasis. Here, we evaluate HIS and LiP0 antigens using two different immunization strategies in the hamster model of visceral leishmaniasis. Hamsters are highly susceptible to L. infantum infection and we demonstrate that immunization with LiP0, but not HIS, protects against the fatal outcome of visceral leishmaniasis. Immunization with LiP0 was able to induce an increased expression of IFN-γ in detriment of IL-10 and TGF-β in the draining lymph node before infection creating an inhospitable environment for parasite growth. Following challenge, a reduced parasite load in the lymph node, spleen and liver of LiP0 immunized hamsters was detected five months after challenge. These findings suggest that LiP0 used in a DNA formulation could be considered a potential component in a vaccine formulation against visceral leishmaniasis.

Efficacy of a slow-release imidacloprid (10%)/flumethrin (4.5%) collar for the prevention of canine leishmaniosis

Background

The efficacy of a slow-release insecticidal and repellent collar containing 10% imidacloprid and 4.5% flumethrin (Seresto, Bayer Animal Health) in preventing Leishmania infantum infection was evaluated in a large population of dogs living in a hyper-endemic area of Sicily (Italy).

Methods

A total of 219 dogs, negative for L. infantum were enrolled in a multicentre, controlled study. Dogs were divided into two homogeneous groups, defined as G1 (n = 102) and G2 (n = 117). Before the start of the sand fly season, dogs in G1 were treated with the collar while animals in G2 were left untreated, serving as negative controls. Dogs were serially sampled on day D90, D180, D210 and D300 in order to assess Leishmania infection by IFAT, PCR on skin (D210-D300) and bone marrow (D300) and cytology on bone marrow aspirate (D300).

Results

Three dogs (2.9%) in G1 and 41 (40.2%) in G2 became positive for L. infantum in at least one of the diagnostic tests employed in the study. The number of seropositive dogs in G2 increased in the course of the study from 15 (D90) to 41 (D300), with some of them also positive in other diagnostic tests. Eight (19.6%) of the seropositive dogs in G2 showed an increase in antibody titers ranging from 1:160 to 1:1,280. At the last follow-up, some of dogs in G2 displayed overt clinical signs suggestive of leishmaniosis. The mean incidence density rate at the final follow-up was 4.0% for G1 and 60.7% for G2, leading to a mean efficacy of the collar in protecting dogs at both sites of 93.4%.

Conclusions

The slow-release collar tested in this study was shown to be safe and highly effective in preventing L. infantum infection in a large population of dogs. Protection conferred by a single collar (up to eight months) spanned an entire sand fly season in a hyper-endemic area of southern Italy. The regular use of collars, at least during the sand fly season, may represent a reliable and sustainable strategy for the prevention of leishmaniosis in dogs living in or travelling to an endemic area.

Successful vaccines for naturally occurring protozoal diseases of animals should guide human vaccine research. A review of protozoal vaccines and their designs

Effective vaccines are available for many protozoal diseases of animals, including vaccines for zoonotic pathogens and for several species of vector-transmitted apicomplexan haemoparasites. In comparison with human diseases, vaccine development for animals has practical advantages such as the ability to perform experiments in the natural host, the option to manufacture some vaccines in vivo, and lower safety requirements. Although it is proper for human vaccines to be held to higher standards, the enduring lack of vaccines for human protozoal diseases is difficult to reconcile with the comparatively immense amount of research funding. Common tactical problems of human protozoal vaccine research include reliance upon adapted rather than natural animal disease models, and an overwhelming emphasis on novel approaches that are usually attempted in replacement of rather than for improvement upon the types of designs used in effective veterinary vaccines. Currently, all effective protozoal vaccines for animals are predicated upon the ability to grow protozoal organisms. Because human protozoal vaccines need to be as effective as animal vaccines, researchers should benefit from a comparison of existing veterinary products and leading experimental vaccine designs. With this in mind, protozoal vaccines are here reviewed.

Leishmaniasp. Amastigotes Identification in Canine Transmissible Venereal Tumor

Leishmaniasis is a vector-borne disease withLeishmania chagasibeing the etiological agent of canine visceral leishmaniasis in South America. Canine venereal tumor is a transplantable round cell tumor of histiocytic origin which is mostly observed in sexually active male and female intact dogs. It has been shown thatLeishmaniaamastigotes have higher tropism for the canine male genital tract tissues and venereal leishmaniasis transmission has been documented in dogs but, to date, a canine venereal tumor-dependent transmission route has not been fully demonstrated. In this report, a 10-year-old, mixed breed, intact female dog presented a vaginal venereal transmissible tumor but no other clinical abnormalities otherwise. Unexpectedly, tumor tissue imprint smears examination revealedLeishmaniasp. amastigotes within infiltrating macrophages. In addition to the cytological direct identification, the protozoan was confirmed within the neoplastic tissue by means of immunohistochemistry and polymerase chain reaction. This report illustrates an asymptomaticLeishmaniasp. infection that may have started on or from the canine venereal tumor tissue, the latter option further supporting previous evidence of such an alternative vector-independent route of transmission for canine visceral leishmaniasis in areas where these diseases coexist.

The prevention of canine leishmaniasis and its impact on public health

Canine leishmaniasis (CanL) caused by Leishmania infantum is a vector-borne disease of great veterinary and medical significance. Prevention of CanL requires a combined approach including measures focused on dogs and the environment where the vectors perpetuate. Over past decades, considerable effort has been put towards developing novel and cost-effective strategies against CanL. Vaccination is considered among the most promising tools for controlling CanL, and synthetic pyrethroids are useful and cost-effective in reducing risk of L. infantum infection in dogs. The effectiveness of the use of vaccines plus repellents in preventing L. infantum infection and subsequent disease development should be assessed by means of large-scale, randomized controlled field trials because this combined strategy may become the next frontier in the control of CanL.

Development of Leishmania vaccines: predicting the future from past and present experience

Leishmaniasis is a disease that ranges in severity from skin lesions to serious disfigurement and fatal systemic infection. Resistance to infection is associated with a T-helper-1 immune response that activates macrophages to kill the intracellular parasite in a nitric oxide-dependent manner. Conversely, disease progression is generally associated with a T-helper-2 response that activates humoral immunity. Current control is based on chemotherapeutic treatments which are expensive, toxic and associated with high relapse and resistance rates. Vaccination remains the best hope for control of all forms of the disease, and the development of a safe, effective and affordable antileishmanial vaccine is a critical global public-health priority. Extensive evidence from studies in animal models indicates that solid protection can be achieved by immunization with defined subunit vaccines or live-attenuated strains of Leishmania. However, to date, no vaccine is available despite substantial efforts by many laboratories. Major impediments in Leishmania vaccine development include: lack of adequate funding from national and international agencies, problems related to the translation of data from animal models to human disease, and the transition from the laboratory to the field. Furthermore, a thorough understanding of protective immune responses and generation and maintenance of the immunological memory, an important but least-studied aspect of antiparasitic vaccine development, during Leishmania infection is needed. This review focuses on the progress of the search for an effective vaccine against human and canine leishmaniasis.

Vaccine Development Against Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani and Leishmania infantum/chagasi represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Zoonotic VL caused by L. infantum is a re-emergent canid zoonoses which represents a complex epidemiological cycle in the New world where domestic dogs serve as a reservoir host responsible for potentially fatal human infection and where dog culling is the only measure for reservoir control. Life-long immunity to VL has motivated development of prophylactic vaccines against the disease but very few have progressed beyond the experimental stage. No licensed vaccine is available till date against any form of leishmaniasis. High toxicity and increasing resistance to the current chemotherapeutic regimens have further complicated the situation in VL endemic regions of the world. Advances in vaccinology, including recombinant proteins, novel antigen-delivery systems/adjuvants, heterologous prime-boost regimens and strategies for intracellular antigen presentation, have contributed to recent advances in vaccine development against VL. Attempts to develop an effective vaccine for use in domestic dogs in areas of canine VL should be pursued for preventing human infection. Studies in animal models and human patients have revealed the pathogenic mechanisms of disease progression and features of protective immunity. This review will summarize the accumulated knowledge of pathogenesis, immune response, and prerequisites for protective immunity against human VL. Authors will discuss promising vaccine candidates, their developmental status and future prospects in a quest for rational vaccine development against the disease. In addition, several challenges such as safety issues, renewed and coordinated commitment to basic research, preclinical studies and trial design will be addressed to overcome the problems faced in developing prophylactic strategies for protection against this lethal infection.

Vaccines for canine leishmaniasis

Leishmaniasis is the third most important vector-borne disease worldwide. Visceral leishmaniasis (VL) is a severe and frequently lethal protozoan disease of increasing incidence and severity due to infected human and dog migration, new geographical distribution of the insect due to global warming, coinfection with immunosuppressive diseases, and poverty. The disease is an anthroponosis in India and Central Africa and a canid zoonosis (ZVL) in the Americas, the Middle East, Central Asia, China, and the Mediterranean. The ZVL epidemic has been controlled by one or more measures including the culling of infected dogs, treatment of human cases, and insecticidal treatment of homes and dogs. However, the use of vaccines is considered the most cost-effective control tool for human and canine disease. Since the severity of the disease is related to the generation of T-cell immunosuppression, effective vaccines should be capable of sustaining or enhancing the T-cell immunity. In this review we summarize the clinical and parasitological characteristics of ZVL with special focus on the cellular and humoral canine immune response and review state-of-the-art vaccine development against human and canine VL. Experimental vaccination against leishmaniasis has evolved from the practice of leishmanization with living parasites to vaccination with crude lysates, native parasite extracts to recombinant and DNA vaccination. Although more than 30 defined vaccines have been studied in laboratory models no human formulation has been licensed so far; however three second-generation canine vaccines have already been registered. As expected for a zoonotic disease, the recent preventive vaccination of dogs in Brazil has led to a reduction in the incidence of canine and human disease. The recent identification of several Leishmania proteins with T-cell epitopes anticipates development of a multiprotein vaccine that will be capable of protecting both humans and dogs against VL.

The development and clinical evaluation of second-generation leishmaniasis vaccines

Infection with Leishmania parasites results in a range of clinical manifestations and outcomes. Control of Leishmania parasite transmission is extremely difficult due to the large number of vectors and potential reservoirs, and none of the current treatments are ideal. Vaccination could be an effective strategy to provide sustained control. In this review, the current global situation with regard to leishmaniasis, the immunology of Leishmania infection and various efforts to identify second generation vaccine candidates are briefly discussed. The variety of clinical trials conducted using the only current second generation vaccine approved for clinical use, LEISH-F1+MPL-SE, are described. Given that epidemiological evidence suggests that reducing the canine reservoir also positively impacts human incidence, efforts at providing a vaccine for leishmaniasis in dogs are highlighted. Finally, potential refinements and surrogate markers that could expedite the introduction of a vaccine that can limit the severity and incidence of leishmaniasis are discussed.

Leishmaniasis

Leishmaniasis is a disease that ranges in severity from skin lesions to serious disfigurement and fatal systemic infection. WHO has classified the disease as emerging and uncontrolled and estimates that the infection results in two million new cases a year. There are 12 million people currently infected worldwide, and leishmaniasis threatens 350 million people in 88 countries. Vaccination remains the best hope for control of all forms of the disease, and the development of a safe, effective and affordable antileishmanial vaccine is a critical global public-health priority. However, to date, no such vaccine is available despite substantial efforts by many laboratories. Main obstacle in vaccine design is the transition from the laboratory to the field and extrapolation of data from animal models to humans. This review discusses recent findings in the antileishmania vaccine field and current difficulties hampering vaccine implementation.

One Health: the global challenge of epidemic and endemic leishmaniasis

'One Health' proposes the unification of medical and veterinary sciences with the establishment of collaborative ventures in clinical care, surveillance and control of cross-species disease, education, and research into disease pathogenesis, diagnosis, therapy and vaccination. The concept encompasses the human population, domestic animals and wildlife, and the impact that environmental changes ('environmental health') such as global warming will have on these populations. Visceral leishmaniasis is a perfect example of a small companion animal disease for which prevention and control might abolish or decrease the suffering of canine and human patients, and which aligns well with the One Health approach. In this review we discuss how surveillance for leishmaniases is undertaken globally through the control of anthroponootic visceral leishmaniasis (AVL) and zoonotic visceral leishmaniasis (ZVL). The ZVL epidemic has been managed to date by the culling of infected dogs, treatment of human cases and control of the sandfly vector by insecticidal treatment of human homes and the canine reservoir. Recently, preventive vaccination of dogs in Brazil has led to reduction in the incidence of the canine and human disease. Vaccination permits greater dog owner compliance with control measures than a culling programme. Another advance in disease control in Africa is provided by a surveillance programme that combines remote satellite sensing, ecological modelling, vector surveillance and geo-spatial mapping of the distribution of vectors and of the animal-to-animal or animal-to-human pathogen transmission. This coordinated programme generates advisory notices and alerts on emerging infectious disease outbreaks that may impede or avoid the spreading of visceral leishmaniasis to new areas of the planet as a consequence of global warming.

Development of Vaccines against Visceral Leishmaniasis

Leishmaniasis is a neglected disease resulting in a global morbidity of 2,090 thousand Disability-Adjusted Life Years and a mortality rate of approximately 60,000 per year. Among the three clinical forms of leishmaniasis (cutaneous, mucosal, and visceral), visceral leishmaniasis (VL) accounts for the majority of mortality, as if left untreated VL is almost always fatal. Caused by infection with Leishmania donovani or L. infantum, VL represents a serious public health problem in endemic regions and is rapidly emerging as an opportunistic infection in HIV patients. To date, no vaccine exists for VL or any other form of leishmaniasis. In endemic areas, the majority of those infected do not develop clinical symptoms and past infection leads to robust immunity against reinfection. Thus the development of vaccine for Leishmania is a realistic public health goal, and this paper summarizes advances in vaccination strategies against VL.

Visceral leishmaniasis: immunology and prospects for a vaccine

Human visceral leishmaniasis (HVL) is the most severe clinical form of a spectrum of neglected tropical diseases caused by protozoan parasites of the genus Leishmania. Caused mainly by L. donovani and L. infantum/chagasi, HVL accounts for more than 50 000 deaths every year. Drug therapy is available but costly, and resistance against several drug classes has evolved. Here, we review our current understanding of the immunology of HVL and approaches to and the status of vaccine development against this disease.

Methods of Control of the Leishmania infantum Dog Reservoir: State of the Art

Leishmania infantum is a protozoan parasite causing severe vector-borne visceral diseases both in humans and dogs. The latter are the most important natural reservoir and therefore should be the main target of control measures. The real efficacy of seropositive dogs culling as a direct control method is still debated, and the new sensitivity of large part of population considers ethically unacceptable this kind of approach. Treatment of infectious dogs with one of the available therapeutic protocols is recommendable as it allows to reduce parasite burdens and therefore the possibility of transmission of Leishmania infantum to vectors. Vaccination has been proven to be a very effective control tool, but the absence of a commonly recognized diagnostic method able to distinguish vaccinate from seropositive individuals is still an important limit. Concerning indirect control methods, a number of studies have demonstrated the efficacy of topical insecticides treatment (collars, spot-on, and sprays) in reducing incidence and prevalence of L. infantum. Also, the reduction of the odds of seroconversion in humans in endemic areas has been reported after the application of indirect control measures on dogs. The contemporary use of direct and indirect methods is even more effective in reducing seroprevalence in dogs.

Humoral immunological profile and parasitological statuses of Leishmune vaccinated and visceral leishmaniasis infected dogs from an endemic area

Dogs represent the major reservoir of Leishmaniao chagasi and vaccination against the canine disease is a potential control strategy. However, seroconversion occurs post-vaccine and hence, there is need to discriminate between the former group and naturally infected dogs. The present study represents a comparison of the humoral immunological profiles of both groups using Leishmania soluble antigen (LSA) and fucose-mannose ligand (FML). For both categories, ear skin samples were evaluated immunohistochemically and through PCR, that was also performed in blood specimens, as well as their ability to infect Lutzomyia (Lutzomyia) longipalpis. All these tests showed negative results for the vaccinated dogs. Differences between groups were observed regarding IgG, IgG2 and IgE absorbances as determined by FML-ELISA, and for IgG1 and IgE absorbances as measured by LSA-ELISA, showing that Leishmune-immunised animals and VL naturally infected dogs present different immunological profiles, even though these differences cannot be used to distinguish between these two groups of dogs.

Immunity to Leishmania and the rational search for vaccines against canine leishmaniasis

The control of infection by Leishmania infantum (syn. Leishmania chagasi) in dogs is essential to stop the current spread of zoonotic visceral leishmaniasis. The past few years have seen significant advances in achieving efficient immunization of dogs and, more than ever before, an effective vaccine against canine leishmaniasis can now be considered a feasible goal. This article summarizes experimental data gathered from recent dog trials aimed at identifying immunological mechanisms implicated in protection against canine infection to discuss their potential to serve as quantitative surrogate markers of immunization and, more importantly, its usefulness to evaluate whether the immunity induced by the vaccine candidate is strong enough to protect against canine leishmaniasis.

DNA vaccines: a rational design against parasitic diseases

Parasitic diseases are one of the most devastating causes of morbidity and mortality worldwide. Although immunization against these infections would be an ideal solution, the development of effective vaccines has been hampered by specific challenges posed by parasitic pathogens. Plasmid-based DNA vaccines may prove to be promising immunization tools in this area because vectors can be designed to integrate several antigens from different stages of the parasite life cycle or different subspecies; vaccines, formulations and immunization protocols can be tuned to match the immune response that offers protective immunity; and DNA vaccination is an affordable platform for developing countries. Partial and full protective immunity have been reported following DNA vaccination against the most significant parasitic diseases in the world.

Vaccine development against Trypanosoma cruzi and Leishmania species in the post-genomic era

Trypanosoma cruzi and the genus Leishmania are protozoan parasites causing diseases of major public health importance, and the recent completion of the sequencing of their genomes has opened new opportunities to further our understanding of the mechanisms required for protection and the development of vaccines. For example, trans-sialidases, one of the largest protein families from T. cruzi, contain dominant CD8+ T cell epitopes, and their use as preventive or therapeutic vaccines in different animal models has provided encouraging results. A much wider range of antigens and vaccine formulations have been tested against Leishmania, and new correlates for protection are being defined, such as the induction of multifunctional Th1 effector cells capable of producing a complex set of cytokines. Also, while a large number of these vaccine candidates have been rather successful in mouse models, their usefulness in more relevant animal models is still poor, in spite of significant immunogenicity. Novel proteomics and genomics approaches are being used for antigen discovery and the identification of new vaccine candidates, some of which have shown promise for the control of infection. These studies cast little doubt that T. cruzi and Leishmania genomes represent major resources for understanding key aspects of the mechanisms of immune protection against these parasites, and the increasing use of these tools will greatly impact vaccine development.

Diminished CD4+/CD25+ T cell and increased IFN-gamma levels occur in dogs vaccinated with Leishmune in an endemic area for visceral leishmaniasis

The Leishmune vaccine has been used in endemic areas to prevent canine visceral leishmaniasis in Brazil, but cytokine production induced by vaccination has rarely been investigated in dogs. This study aimed to evaluate the immune response of dogs vaccinated with Leishmune FML vaccine (Fort Dodge) against total antigen of Leishmania (Leishmania) chagasi (TAg) and FML. Twenty healthy dogs from Araçatuba, São Paulo, Brazil, an endemic leishmaniasis area, received three consecutive subcutaneous injection of Leishmune vaccine at 21-day intervals. PBMC were isolated before and 10 days after completing vaccination and lymphoproliferative response and antibody production against FML or total promastigote antigen were tested. Cytokines IFN-gamma, IL-4 and TNF-alpha were measured in culture supernatant and CD4+/CD25+ and CD8+/CD25+ T cell presence was determined. Analysis of the data indicated that the vaccine conferred humoral responses (100%) against both antigens and cellular immunity to FML (85%) and total antigen (80%), the supernatant of cultured cells stimulated with TAg and FML showed an increase in IFN-gamma (P<0.05), and the vaccine reduced CD4+/CD25+ T cell presence compared to that observed before vaccination. These responses may constitute part of the immune mechanism induced by Leishmune.

Immunotherapy with the saponin enriched-Leishmune vaccine versus immunochemotherapy in dogs with natural canine visceral leishmaniasis

Leishmune, the first licensed vaccine for prophylaxis against canine visceral leishmaniasis (CVL) and is also immunotherapeutic when used with double saponin adjuvant concentration. The Leishmune therapeutic vaccine was assessed for immunotherapy (IT) in 31 infected dogs and for immunochemotherapy (ICT) in combination with allopurinol or amphotericinB/allopurinol, in 35 dogs. Compared to infected untreated control dogs, at month 3, both treatments increased the proportion of dogs showing intradermal response to Leishmania antigen to a similar extent (from 8 to 67%, in the IT and to 76%, in the ICT groups), and conversely reduced from 100 to 38% (IT) and to 18% (ICT) the proportion of symptomatic cases, from 54 to 12% (IT) and to 15% (ICT) the proportion of parasite evidence in lymph nodes and from 48 to 19% (IT) and 12% (ICT) the proportion of deaths, indicating that the immunotherapy with enriched-Leishmune vaccine promotes the control of the clinical and parasitological signs of CVL rendering most dogs asymptomatic although PCR positive. By month 8, negative lymph node PCR results were obtained in 80% of the ICT-treated dogs, but only in 33% of the IT group (p=0.0253), suggesting that the combination of additional chemotherapy with Leishmune-enriched saponin vaccination abolished, not only the symptoms but also the latent infection condition, curing the dogs. The animals were followed up until 4.5 years after the beginning of the experiment and, compared to the untreated control group at month 3 (12/25 dogs; 48%), a decrease in the rate of CVL deaths was only seen after ICT treatment (7/35 dogs; 20%; 0.0273) but not after IT treatment (10/31 dogs; 32%; p=0.278), pointing out an additional advantage of the ICT treatment with the enriched-Leishmune in the control and cure of CVL.

The chimerical multi-component Q protein from Leishmania in the absence of adjuvant protects dogs against an experimental Leishmania infantum infection

The protective potential against Leishmania infection of the Leishmania chimerical Q protein administered as a single (Q) or double dose (Q+Q) without adjuvant was analyzed in a double-blind placebo controlled experiment in dogs. During vaccination the protein induced an intense early anti-Q response but no reactivity against total Leishmania infantum proteins was detected. Several end-points were taken into consideration. In the vaccinated animals the amount and intensity of clinical symptoms was lower than in the control group. Pathological signs of disease were observed in liver, kidney and spleen of all dogs from the control group in contrast to the normal appearance of the organs of the vaccinated animals. Vaccination was able to induce parasite clearance in most dogs. Only 1/7 dog was parasite DNA positive in skin in the Q group in contrast to 6/7 dogs in control and 4/7 in Q+Q. Significant anti-SLA clearance was observed in the vaccinated animals at the end of the study. Differences between control and vaccinated animals were also observed at the biochemical level, DTH and nitrite oxide production.

Directions for the diagnosis, clinical staging, treatment and prevention of canine leishmaniosis

Canine leishmaniosis (CanL) due to Leishmania infantum is a life threatening zoonotic disease with a wide distribution in four continents and importance also in non-endemic regions. The purpose of this report is to present a consensus of opinions on the diagnosis, treatment, prognosis and prevention of CanL in order to standardize the management of this infection. CanL is a disease in which infection does not equal clinical illness due to the high prevalence of subclinical infection among endemic canine populations. The most useful diagnostic approaches include serology by quantitative techniques and PCR. High antibody levels are associated with severe parasitism and disease and are diagnostic of clinical leishmaniosis. However, the presence of lower antibody levels is not necessarily indicative of disease and further work-up is necessary to confirm CanL by other diagnostic methods such as cytology, histopathology and PCR. We propose a system of four clinical stages, based on clinical signs, clinicopathological abnormalities and serological status. Suitable therapy and expected prognosis are presented for each of the stages. The combination of meglumine antimoniate and allopurinol constitutes the first line pharmaceutical protocol. However, although most dogs recover clinically after therapy, complete elimination of the parasite is usually not achieved and infected dogs may eventually relapse. Follow-up of treated dogs with blood counts, serum biochemistry, urinalysis, serology and PCR is essential for prevention of relapses. Protection against sand fly bites by topical insecticides is effective in reducing infection, and recent development of vaccines has indicated that prevention by vaccination is feasible.

Sand fly salivary proteins induce strong cellular immunity in a natural reservoir of visceral leishmaniasis with adverse consequences for Leishmania

Immunity to a sand fly salivary protein protects against visceral leishmaniasis (VL) in hamsters. This protection was associated with the development of cellular immunity in the form of a delayed-type hypersensitivity response and the presence of IFN-gamma at the site of sand fly bites. To date, there are no data available regarding the cellular immune response to sand fly saliva in dogs, the main reservoirs of VL in Latin America, and its role in protection from this fatal disease. Two of 35 salivary proteins from the vector sand fly Lutzomyia longipalpis, identified using a novel approach termed reverse antigen screening, elicited strong cellular immunity in dogs. Immunization with either molecule induced high IgG(2) antibody levels and significant IFN-gamma production following in vitro stimulation of PBMC with salivary gland homogenate (SGH). Upon challenge with uninfected or infected flies, immunized dogs developed a cellular response at the bite site characterized by lymphocytic infiltration and IFN-gamma and IL-12 expression. Additionally, SGH-stimulated lymphocytes from immunized dogs efficiently killed Leishmania infantum chagasi within autologous macrophages. Certain sand fly salivary proteins are potent immunogens obligatorily co-deposited with Leishmania parasites during transmission. Their inclusion in an anti-Leishmania vaccine would exploit anti-saliva immunity following an infective sand fly bite and set the stage for a protective anti-Leishmania immune response.

Decrease of the incidence of human and canine visceral leishmaniasis after dog vaccination with Leishmune in Brazilian endemic areas

Leishmune, the first prophylactic vaccine licensed against canine visceral leishmaniasis (CVL), has been used in Brazil since 2004, where seropositive dogs are sacrificed in order to control human visceral leishmaniasis (VL). We demonstrate here that vaccination with Leishmune does not interfere with the serological control campaign (110,000 dogs). Only 1.3% of positivity (76 among 5860) was detected among Leishmune uninfected vaccinees. We also analyzed the possible additive effect of Leishmune vaccination over dog culling, on the decrease of the incidence of CVL and VL in two Brazilian endemic areas, from 2004 to 2006. In Araçatuba, a 25% of decline was seen in CVL with a 61% decline in human cases, indicating the additive effect of Leishmune vaccination of 5.7% of the healthy dogs (1419 dogs), on regular dog culling. In Belo Horizonte (BH), rising curves of canine and human incidence were observed in the districts of Barreiro, Venda Nova and Noroeste, while the canine and human incidence of Centro Sul, Leste, Nordeste, Norte, Pampulha and Oeste, started to decrease or maintained a stabilized plateau after Leishmune vaccination. Among the districts showing a percent decrease of human incidence (-36.5%), Centro Sul and Pampulha showed the highest dog vaccination percents (63.27% and 27.27%, respectively) and the lowest dog incidence (-3.36% and 1.89%, respectively). They were followed by Oeste, that vaccinated 25.30% of the animals and experienced an increase of only 12.86% of dog incidence and by Leste and Nordeste, with lower proportions of vaccinees (11.72% and 10.76%, respectively) and probably because of that, slightly higher canine incidences (42.77% and 35.73%). The only exception was found in Norte district where the reduced human and canine incidence were not correlated to Leishmune vaccination. Much lower proportions of dogs were vaccinated in Venda Nova (4.35%), Noroeste (10.27%) and Barreiro (0.09%) districts, which according to that exhibited very increased canine incidences (24.48%, 21.85% and 328.57%, respectively), and pronounced increases in human incidence (14%, 4% and 17%, respectively). The decrease of canine (p=-0.008) and human incidences (p=-0.048) is directly correlated to the increase of the number of vaccinated dogs, confirming the additive control effect of Leishmune vaccination over dog culling, reducing the parasite reservoir, protecting dogs and, in this way, reducing the risk of transmission of VL to humans and becoming a new effective control tool.

Immunogenicity assay of the Leishmune vaccine against canine visceral leishmaniasis in Brazil

Leishmune is the industrialized version of the FML-saponin vaccine which has been shown to develop 92-95% protection in vaccinated dogs and 76-80% vaccine efficacy against field canine visceral leishmaniasis (CVL) in Brazil. Leishmune has been proven to be safe and tolerable and a transmission-blocking vaccine which renders vaccinated dogs non-infectious to sand fly vectors. In the present investigation, 550 healthy seronegative dogs of endemic and epidemic areas of Brazil were monitored for Leishmune-induced immunogenicity during a 2-year trial. Another group of 588 untreated exposed dogs was also studied in parallel. Both groups were seronegative on day 0. The strong immunogenicity induced by Leishmune vaccine was demonstrated by the 98% of FML-seroconversion, increase in absorbencies, the 82.7% DTH positive reactions and increase in skin test size diameters, the average increase in CD8+ total lymphocytes population in blood (27.1%), expected for QS21 saponin-containing vaccine, the sustained proportions of CD4+ T cells, and the average increased proportions of CD21+ B lymphocytes (42.3%). The Leishmune-induced protection against CVL is demonstrated by the results: 98.8% asymptomatic dogs (at the end of first year) and 99% healthy survivors (at the end of the second year) among vaccinated dogs, compared to the 79.4% asymptomatic and 61% survivor dogs (p<0.001) monitored in the untreated exposed cohort. In spite of the low vaccine coverage, it was possible to detect a 66.1% (p<0.005) reduction in Belo Horizonte and an 80.2% (p<0.005) reduction in Araçatuba of the incidence of CVL among vaccinated dogs, when compared to the global incidence of CVL of each town, respectively. Our preliminary results support the potential use of Leishmune to prevent CVL epidemics.