Cross-protective immunity against leptospirosis elicited by a live, attenuated lipopolysaccharide mutant

Evaluation of protective efficacy, serological responses, and cytokine modulation induced by polyvalent Leptospira vaccines in hamsters

Whole-cell inactivated vaccines (bacterins) are the only licensed vaccines available for leptospirosis prevention and control, especially in domestic and farm animals. However, despite their widespread use, inconsistencies in their efficacy have been reported. Because immunity induced by bacterins is mainly mediated by antibodies against leptospiral lipopolysaccharides, the involvement of cellular responses is not well-known. The aim of this study was to investigate the efficacy and characterize the humoral and cellular immune responses induced by whole-cell inactivated leptospirosis bacterin formulations containing serovars Bratislava, Canicola, Copenhageni, Grippotyphosa, Hardjoprajitno, and Pomona. For the potency test, hamsters were immunized with one dose of polyvalent bacterins (either commercial or experimental) and then challenged with a virulent Pomona strain. Serological (MAT and IgM and IgG-ELISA) and cellular (cytokine transcription in blood evaluated by RT-qPCR) analyses were performed. The results revealed that vaccination with either bacterin formulation was able to protect 90-100% of the hamsters infected with the Pomona serovar, although most of the surviving animals remained as renal carriers. Specific agglutinating antibodies and significant levels of IgM, IgG, and IgG2 (P < 0.05) that were able to react with the six serovars present in the vaccine formulations were produced, indicating that the vaccines can potentially provide immunity against all strains. The protective immunity of these vaccines was mainly mediated by balanced a Th1/Th2 response, characterized by increased IFN-γ, IL-10 and IL-α transcription. These data support the importance of characterizing immunological responses involved in bacterin efficacy and investing in the improvement of these vaccine formulations.

Leptospira Lipid A Is a Potent Adjuvant That Induces Sterilizing Immunity against Leptospirosis

Leptospirosis is a globally significant zoonotic disease. The current inactivated vaccine offers protection against specific serovars but does not provide complete immunity. Various surface antigens, such as Leptospira immunoglobulin-like proteins (LigA and LigB), have been identified as potential subunit vaccine candidates. However, these antigens require potent adjuvants for effectiveness. Bacterial lipopolysaccharides (LPSs), including lipid A, are a well-known immunostimulant, and clinical adjuvants often contain monophosphoryl lipid A (MPLA). Being less endotoxic, we investigated the adjuvant properties of lipid A isolated from L. interrogans serovar Pomona (PLA) in activating innate immunity and enhancing antigen-specific adaptive immune responses. PLA activated macrophages to a similar degree as MPLA, albeit at a higher dose, suggesting that it is less potent in stimulation than MPLA. Mice immunized with a variable portion of LigA (LAV) combined with alum and PLA (LAV-alum-PLA) exhibited significantly higher levels of LAV-specific humoral and cellular immune responses compared to alum alone but similar to those induced by alum-MPLA. The adjuvant activity of PLA resembles that of MPLA and is primarily achieved through the increased recruitment, activation, and uptake of antigens by innate immune cells. Furthermore, like MPLA, PLA formulation establishes a long-lasting memory response. Notably, PLA demonstrated superior potency than MPLA formulation and provided sterilizing immunity against the leptospirosis in a hamster model. Overall, our study sheds light on the adjuvant properties of Leptospira lipid A and offers promising avenues for developing LPS-based vaccines against this devastating zoonotic disease.

Lipid A structural diversity among members of the genus Leptospira

Lipid A is the hydrophobic component of bacterial lipopolysaccharide and an activator of the host immune system. Bacteria modify their lipid A structure to adapt to the surrounding environment and, in some cases, to evade recognition by host immune cells. In this study, lipid A structural diversity within the Leptospira genus was explored. The individual Leptospira species have dramatically different pathogenic potential that ranges from non-infectious to life-threatening disease (leptospirosis). Ten distinct lipid A profiles, denoted L1-L10, were discovered across 31 Leptospira reference species, laying a foundation for lipid A-based molecular typing. Tandem MS analysis revealed structural features of Leptospira membrane lipids that might alter recognition of its lipid A by the host innate immune receptors. Results of this study will aid development of strategies to improve diagnosis and surveillance of leptospirosis, as well as guide functional studies on Leptospira lipid A activity.

Challenges for the development of a universal vaccine against leptospirosis revealed by the evaluation of 22 vaccine candidates

Leptospirosis is a neglected disease of man and animals that affects nearly half a million people annually and causes considerable economic losses. Current human vaccines are inactivated whole-cell preparations (bacterins) of Leptospira spp. that provide strong homologous protection yet fail to induce a cross-protective immune response. Yearly boosters are required, and serious side-effects are frequently reported so the vaccine is licensed for use in humans in only a handful of countries. Novel universal vaccines require identification of conserved surface-exposed epitopes of leptospiral antigens. Outer membrane β-barrel proteins (βb-OMPs) meet these requirements and have been successfully used as vaccines for other diseases. We report the evaluation of 22 constructs containing protein fragments from 33 leptospiral βb-OMPs, previously identified by reverse and structural vaccinology and cell-surface immunoprecipitation. Three-dimensional structures for each leptospiral βb-OMP were predicted by I-TASSER. The surface-exposed epitopes were predicted using NetMHCII 2.2 and BepiPred 2.0. Recombinant constructs containing regions from one or more βb-OMPs were cloned and expressed in Escherichia coli. IMAC-purified recombinant proteins were adsorbed to an aluminium hydroxide adjuvant to produce the vaccine formulations. Hamsters (4-6 weeks old) were vaccinated with 2 doses containing 50 – 125 μg of recombinant protein, with a 14-day interval between doses. Immunoprotection was evaluated in the hamster model of leptospirosis against a homologous challenge (10 – 20× ED₅₀) with L. interrogans serogroup Icterohaemorrhagiae serovar Copenhageni strain Fiocruz L1-130. Of the vaccine formulations, 20/22 were immunogenic and induced significant humoral immune responses (IgG) prior to challenge. Four constructs induced significant protection (100%, P < 0.001) and sterilizing immunity in two independent experiments, however, this was not reproducible in subsequent evaluations (0 – 33.3% protection, P > 0.05). The lack of reproducibility seen in these challenge experiments and in other reports in the literature, together with the lack of immune correlates and commercially available reagents to characterize the immune response, suggest that the hamster may not be the ideal model for evaluation of leptospirosis vaccines and highlight the need for evaluation of alternative models, such as the mouse.

Pathogenic Leptospires Limit Dendritic Cell Activation Through Avoidance of TLR4 and TRIF Signaling

Leptospira interrogans is a bacterial species responsible for leptospirosis, a neglected worldwide zoonosis. Mice and rats are resistant and can become asymptomatic carriers, whereas humans and some other mammals may develop severe forms of leptospirosis. Uncommon among spirochetes, leptospires contain lipopolysaccharide (LPS) in their outer membrane. LPS is highly immunogenic and forms the basis for a large number of serovars. Vaccination with inactivated leptospires elicits a protective immunity, restricted to serovars with related LPS. This protection that lasts in mice, is not long lasting in humans and requires annual boosts. Leptospires are stealth pathogens that evade the complement system and some pattern recognition receptors from the Toll-like (TLR) and Nod-Like families, therefore limiting antibacterial defense. In macrophages, leptospires totally escape recognition by human TLR4, and escape the TRIF arm of the mouse TLR4 pathway. However, very little is known about the recognition and processing of leptospires by dendritic cells (DCs), although they are crucial cells linking innate and adaptive immunity. Here we tested the activation of primary DCs derived from human monocytes (MO-DCs) and mouse bone marrow (BM-DCs) 24h after stimulation with saprophytic or different pathogenic virulent or avirulent L. interrogans. We measured by flow cytometry the expression of DC-SIGN, a lectin involved in T-cell activation, co-stimulation molecules and MHC-II markers, and pro- and anti-inflammatory cytokines by ELISA. We found that exposure to leptospires, live or heat-killed, activated dendritic cells. However, pathogenic L. interrogans, especially from the Icterohaemorraghiae Verdun strain, triggered less marker upregulation and less cytokine production than the saprophytic Leptospira biflexa. In addition, we showed a better activation with avirulent leptospires, when compared to the virulent parental strains in murine BM-DCs. We did not observe this difference in human MO-DCs, suggesting a role for TLR4 in DC stimulation. Accordingly, using BM-DCs from transgenic deficient mice, we showed that virulent Icterohaemorraghiae and Manilae serovars dampened DC activation, at least partly, through the TLR4 and TRIF pathways. This work shows a novel bacterial immune evasion mechanism to limit DC activation and further illustrates the role of the leptospiral LPS as a virulence factor.

Revisiting the Development of Vaccines Against Pathogenic Leptospira: Innovative Approaches, Present Challenges, and Future Perspectives

Human vaccination against leptospirosis has been relatively unsuccessful in clinical applications despite an expressive amount of vaccine candidates has been tested over years of research. Pathogenic Leptospira encompass a great number of serovars, most of which do not cross-react, and there has been a lack of genetic tools for many years. These obstacles have hampered the understanding of the bacteria's biology and, consequently, the identification of an effective antigen. Thus far, many approaches have been used in an attempt to find a cost-effective and broad-spectrum protective antigen(s) against the disease. In this extensive review, we discuss several strategies that have been used to develop an effective vaccine against leptospirosis, starting with Leptospira-inactivated bacterin, proteins identified in the genome sequences of pathogenic Leptospira, including reverse vaccinology, plasmid DNA, live vaccines, chimeric multi-epitope, and toll- and nod-like receptors agonists. This overview should be able to guide scientists working in the field to select potential antigens and to choose the appropriate formulation to administer the candidates.

Emergency vaccine immunization protects hamsters against acute leptospirosis

Leptospirosis, caused by pathogenic Leptospira, is a global critical zoonotic disease in terms of mortality and morbidity. Vaccines are often used to prevent leptospirosis. However, few studies have reported the therapeutic effect of a vaccine against Leptospira infection. This study demonstrates the efficacy of the emergency vaccine immunization against acute leptospirosis in hamsters. Treatment with a whole-cell vaccine (Leptospira interrogans serovar Lai) at 24 h post-infection improved the survival rate of hamsters with lower leptospiral burden and minor pathological damage to organs. The vaccine also protected against multiple Leptospira serotypes acute infection. However, the protective effect of the vaccines was lost when beginning treatment at 36 h or 48 h post-infection. These results indicated that vaccines could treat acute leptospirosis in hamsters, but only if immunization is within 24 h after infection.

Protective efficacy of whole-cell inactivated Leptospira vaccines made using virulent or avirulent strains in a hamster model

Whole-cell inactivated vaccines remain the only licensed vaccines used to control human and animal leptospirosis worldwide. Although they are protective against lethal infections, the efficacy of these vaccines has been divergent. The manufacturing process often involves the use of standard bacterial strains subjected to serial in vitro passages, with a risk of loss of virulence, and may affect the immunogenicity and consequently decrease protection. Thus, the objective of this study was to perform a comparative analysis of the efficacy of in-house bacterins produced with standard (avirulent) and virulent strains. Hamsters were immunized with killed bacteria produced using avirulent and virulent strains of L. interrogans serovars Copenhageni and Canicola. Vaccine efficacy was determined in terms of protection against lethal homologous or heterologous challenges. The results showed that immunization with both avirulent and virulent Canicola strains resulted in 100% protection against homologous challenge. Conversely, Copenhageni bacterins produced using an avirulent strain conferred only 25-37.5% protection against homologous challenge (P > 0.05), while virulent Copenhageni bacterin conferred 100% protection (P < 0.001). A single vaccine dose was sufficient to induce protection, and administration of a prime boost significantly reduced the bacterial load in the kidneys and improved the humoral immune response to the virulent Copenhageni strain. These findings suggest that the maintenance of virulent strains in bacterin formulations is essential for improving the immunogenicity and efficacy of leptospirosis vaccines.

Identification of in vivo expressed proteins in live attenuated lipopolysaccharide mutant that mediates heterologous protection against Leptospira spp

Leptospirosis vaccines that elicit broad protection against a range of pathogenic Leptospira spp. would overcome a major drawback of currently licensed bacterin vaccines. Live attenuated vaccine produced from a lipopolysaccharide (LPS) mutant strain of L. interrogans serovar Manilae M1352 (Live M1352) stimulated better protective efficacy than heat killed M1352 (HK M1352) against a heterologous challenge with L. interrogans serovar Pomona. To identify antigens of Live M1352 potentially responsible for cross protection, in vivo-induced antigen technology (IVIAT), a powerful tool to identify in vivo-induced (ivi) genes expressed during infection, was employed in this study. Pooled sera from hamsters immunized with Live M1352 were sequentially adsorbed with various preparations of in vitro grown M1352. The pre-adsorbed sera were used to screen a genomic expression library of M1352. Nineteen strongly reactive clones were selected for DNA sequencing. These ivi genes are conserved in most Leptospira strains. Four selected genes including LIMLP_04965 (tolB), LIMLP_01535, LIMLP_06785 (fliI), and LIMLP_14930 were confirmed for their upregulated expression in kidneys of infected hamsters by RT-qPCR, suggesting their role in leptospiral infection. These ivi proteins represent potential targets for vaccine candidates that warrant further investigation for their protective efficacy.

Applied Proteomics in 'One Health'

‘One Health’ summarises the idea that human health and animal health are interdependent and bound to the health of ecosystems. The purpose of proteomics methodologies and studies is to determine proteins present in samples of interest and to quantify changes in protein expression during pathological conditions. The objectives of this paper are to review the application of proteomics technologies within the One Health concept and to appraise their role in the elucidation of diseases and situations relevant to One Health. The paper develops in three sections. Proteomics Applications in Zoonotic Infections part discusses proteomics applications in zoonotic infections and explores the use of proteomics for studying pathogenetic pathways, transmission dynamics, diagnostic biomarkers and novel vaccines in prion, viral, bacterial, protozoan and metazoan zoonotic infections. Proteomics Applications in Antibiotic Resistance part discusses proteomics applications in mechanisms of resistance development and discovery of novel treatments for antibiotic resistance. Proteomics Applications in Food Safety part discusses the detection of allergens, exposure of adulteration, identification of pathogens and toxins, study of product traits and characterisation of proteins in food safety. Sensitive analysis of proteins, including low-abundant ones in complex biological samples, will be achieved in the future, thus enabling implementation of targeted proteomics in clinical settings, shedding light on biomarker research and promoting the One Health concept.

A live attenuated-vaccine model confers cross-protective immunity against different species of the Leptospira genus

Leptospirosis is the leading zoonotic disease in terms of morbidity and mortality worldwide. Effective prevention is urgently needed as the drivers of disease transmission continue to intensify. The key challenge has been developing a widely applicable vaccine that protects against the >300 serovars that can cause leptospirosis. Live attenuated mutants are enticing vaccine candidates and poorly explored in the field. We evaluated a recently characterized motility-deficient mutant lacking the expression of a flagellar protein, FcpA. Although the fcpA- mutant has lost its ability to cause disease, transient bacteremia was observed. In two animal models, immunization with a single dose of the fcpA- mutant was sufficient to induce a robust anti-protein antibodies response that promoted protection against infection with different pathogenic Leptospira species. Furthermore, characterization of the immune response identified a small repertoire of biologically relevant proteins that are highly conserved among pathogenic Leptospira species and potential correlates of cross-protective immunity.

Leptospiral Immunoglobulin-Like Domain Proteins: Roles in Virulence and Immunity

The virulence mechanisms required for infection and evasion of immunity by pathogenic Leptospira species remain poorly understood. A number of L. interrogans surface proteins have been discovered, lying at the interface between the pathogen and host. Among these proteins, the functional properties of the Lig (leptospiral immunoglobulin-like domain) proteins have been examined most thoroughly. LigA, LigB, and LigC contain a series of, 13, 12, and 12 closely related domains, respectively, each containing a bacterial immunoglobulin (Big) -like fold. The multidomain region forms a mostly elongated structure that exposes a large surface area. Leptospires wield the Lig proteins to promote interactions with a range of specific host proteins, including those that aid evasion of innate immune mechanisms. These diverse binding events mediate adhesion of L. interrogans to the extracellular matrix, inhibit hemostasis, and inactivate key complement proteins. These interactions may help L. interrogans overcome the physical, hematological, and immunological barriers that would otherwise prevent the spirochete from establishing a systemic infection. Despite significant differences in the affinities of the LigA and LigB proteins for host targets, their functions overlap during lethal infection of hamsters; virulence is lost only when both ligA and ligB transcription is knocked down simultaneously. Lig proteins have been shown to be promising vaccine antigens through evaluation of a variety of different adjuvant strategies. This review serves to summarize current knowledge of Lig protein roles in virulence and immunity and to identify directions needed to better understand the precise functions of the Lig proteins during infection.

A Comparison of Intramuscular and Subcutaneous Administration of LigA Subunit Vaccine Adjuvanted with Neutral Liposomal Formulation Containing Monophosphoryl Lipid A and QS21

Leptospirosis vaccines with higher potency and reduced adverse effects are needed for human use. The carboxyl terminal domain of leptospiral immunoglobulin like protein A (LigAc) is currently the most promising candidate antigen for leptospirosis subunit vaccine. However, LigAc-based vaccines were unable to confer sterilizing immunity against Leptospira infection in animal models. Several factors including antigen properties, adjuvant, delivery system, and administration route need optimization to maximize vaccine efficacy. Our previous report demonstrated protective effects of the recombinant LigAc (rLigAc) formulated with liposome-based adjuvant, called LMQ (neutral liposome combined with monophosphoryl lipid A and Quillaja saponaria fraction 21) in hamsters. This study aimed to evaluate the impact of two commonly used administration routes, intramuscular (IM) and subcutaneous (SC), on immunogenicity and protective efficacy of rLigAc-LMQ administrated three times at 2-week interval. Two IM vaccinations triggered significantly higher levels of total anti-rLigAc IgG than two SC injections. However, comparable IgG titers and IgG2/IgG1 ratio was observed for both routes after the third immunization. The route of vaccine administration did not influence the survival rate (60%) and renal colonization against lethal Leptospira challenge. Importantly, the kidneys of IM group showed no pathological lesions while the SC group showed mild damage. In conclusion, IM vaccination with rLigAc-LMQ not only elicited faster antibody production but also protected from kidney damage following leptospiral infection better than SC immunization. However, both tested routes did not influence protective efficacy in terms of survival rate and the level of renal colonization.

New strategies for Leptospira vaccine development based on LPS removal

Pathogenic spirochetes from genus Leptospira are etiologic agents of leptospirosis. Cellular vaccines against Leptospira infection often elicit mainly response against the LPS antigen of the serovars present in the formulation. There is no suitable protein candidate capable of replacing whole-cell vaccines, thus requiring new approaches on vaccine development to improve leptospirosis prevention. Our goal was to develop a whole-cell vaccine sorovar-independent based on LPS removal and conservation of protein antigens exposure, to evaluate the protective capacity of monovalent or bivalent vaccines against homologous and heterologous virulent Leptospira in hamster. Leptospire were subjected to heat inactivation, or to LPS extraction with butanol and in some cases further inactivation with formaldehyde. Hamsters were immunized and challenged with homologous or heterologous virulent serovars, blood and organs were collected from the survivors for bacterial quantification, chemokine evaluation, and analysis of sera antibody reactivity and cross-reactivity by Western blot. Immunization with either heated or low LPS vaccines with serovar Copenhageni or Canicola resulted in 100% protection of the animals challenged with homologous virulent bacteria. Notably, different from the whole-cell vaccine, the low LPS vaccines produced with serovar Canicola provided only partial protection in heterologous challenge with the virulent Copenhageni serovar. Immunization with bivalent formulation results in 100% protection of immunized animals challenged with virulent serovar Canicola. All vaccines produced were able to eliminate bacteria from the kidney of challenged animals. All the vaccines raised antibodies capable to recognize antigens of serovars not present in the vaccine formulation. Transcripts of IFNγ, CXCL16, CCL5, CXCL10, CXCR6, and CCR5, increased in all immunized animals. Conclusion: Our results showed that bivalent vaccines with reduced LPS may be an interesting strategy for protection against heterologous virulent serovars. Besides the desirable multivalent protection, the low LPS vaccines are specially promising due to the expected lower reatogenicity.

Role of Supramolecule ErpY-Like Lipoprotein of Leptospira in Thrombin-Catalyzed Fibrin Clot Inhibition and Binding to Complement Factors H and I, and Its Diagnostic Potential

Leptospirosis is one of the most widespread zoonoses caused by pathogenic Leptospira spp. In this study, we report that the LIC11966/ErpY-like lipoprotein is a surface-exposed outer membrane protein exclusively present in pathogenic species of Leptospira The recombinant ErpY (rErpY)-like protein is recognized by the immunoglobulins of confirmed leptospirosis sera of diverse hosts (human, bovine, and canine), suggesting the expression of the native leptospiral surface protein during infection. Circular dichroism of pure rErpY-like protein showed the secondary structural integrity to be uncompromised during the purification process. Analysis of the rErpY-like protein by native polyacrylamide gel electrophoresis, chemical cross-linking, dynamic light scattering, and field emission transmission electron microscopy demonstrated it undergoes supramolecular assembly. The rErpY-like protein can bind to diverse host extracellular matrices, and it presented a saturable and strong binding affinity (dissociation constant [K_D ] of 70.45 ± 4.13 nM) to fibrinogen, a central host plasma component involved in blood clotting. In the presence of the rErpY-like supramolecule, thrombin-catalyzed fibrin clot formation is inhibited up to 7%, implying its role in inhibiting blood coagulation during Leptospira infection. In addition, binding of the rErpY-like supramolecule to complement factors H and I suggests the protein also contributes to Leptospira evading innate host defense during infection by inactivating alternative complement pathways. This study reveals that rErpY-like protein is functionally active in the supramolecular state and performs moonlighting activity under the given in vitro conditions.

Reduced Renal Colonization and Enhanced Protection by Leptospiral Factor H Binding Proteins as a Multisubunit Vaccine Against Leptospirosis in Hamsters

Subunit vaccines conferring complete protection against leptospirosis are not currently available. The interactions of factor H binding proteins (FHBPs) on pathogenic leptospires and host factor H are crucial for immune evasion by inhibition of complement-mediated killing. The inhibition of these interactions may be a potential strategy to clear leptospires in the host. This study aimed to evaluate a multisubunit vaccine composed of four known leptospiral FHBPs: LigA domain 7–13 (LigAc), LenA, LcpA, and Lsa23, for its protective efficacy in hamsters. The mono and multisubunit vaccines formulated with LMQ adjuvant, a combination of neutral liposome, monophosphoryl lipid A, and Quillaja saponaria fraction 21, induced high and comparable specific antibody (IgG) production against individual antigens. Hamsters immunized with the multisubunit vaccine showed 60% survival following the challenge by 20× LD₅₀ of Leptospira interrogans serovar Pomona. No significant difference in survival rate and pathological findings of target organs was observed after vaccinations with multisubunit or mono-LigAc vaccines. However, the multisubunit vaccine significantly reduced leptospiral burden in surviving hamsters in comparison with the monosubunit vaccines. Therefore, the multisubunit vaccine conferred partial protection and reduced renal colonization against virulence Leptospira infection in hamsters. Our multisubunit formulation could represent a promising vaccine against leptospirosis.

Toolbox of Molecular Techniques for Studying Leptospira Spp

This chapter covers the progress made in the Leptospira field since the application of mutagenesis techniques and how they have allowed the study of virulence factors and, more generally, the biology of Leptospira. The last decade has seen advances in our ability to perform molecular genetic analysis of Leptospira. Major achievements include the generation of large collections of mutant strains and the construction of replicative plasmids, enabling complementation of mutations. However, there are still no practical tools for routine genetic manipulation of pathogenic Leptospira strains, slowing down advances in pathogenesis research. This review summarizes the status of the molecular genetic toolbox for Leptospira species and highlights new challenges in the nascent field of Leptospira genetics.

Seroprevalence of leptospirosis in human groups at risk due to environmental, labor or social conditions

Leptospirosis is important in Uruguay due to the economic loss caused by the diseases of production animals, mainly bovines, and also due to frequent human infection. We decided to study anti-Leptospira antibodies in the sera of dairy workers, rice laborers, veterinarians, suburban slum dwellers and garbage recyclers. Our aims were to estimate the seroprevalence of infection by Leptospira spp. in these people at risk, the relative importance of the known risk factors associated with infection, and the impact of human infections in each setting. Groups at risk were identified and 35 visits to their locations were made, conducting field surveys and exchange talks for information and education. Simple epidemiological questionnaires were administered and sera samples were taken from 308 persons. The microagglutination Technique (MAT) and the IgM Indirect Immunofluorescence (IIF) assay were employed to detect antibodies. Environmental water samples, canine and equine sera were also examined. More than 45% of human sera were reactive and the studied groups were confirmed to be widely exposed to infection. Female sera were frequently reactive, though most illnesses occur in men, and the most severe cases in elderly males; the emergence and evolution of the disease may strongly depend on the host condition and functions. Animal contact and unsafe water usage were the main identified risk factors to be considered in prevention. Fifty per cent of the studied horses showed a positive MAT reaction. The underdiagnosis of the illness and its long-term symptoms require further study, as well as greater health and social attention efforts.

Evaluation of different strategies to promote a protective immune response against leptospirosis using a recombinant LigA and LigB chimera

Leptospirosis is a zoonosis of worldwide distribution, caused by infection with pathogenic Leptospira species. The vaccines that are currently available are bacterins, with limited human use, that confer short-term, serovar-specific immunity. Lig proteins are considered to be the best vaccine candidates to date. Here, we aimed to construct a recombinant Lig chimera (LC) comprised of LigAni and LigBrep fragments, and to evaluate it as subunit or DNA vaccine using different administration strategies. Vaccines were formulated with 50 µg of recombinant LC associated with different adjuvants or with 100 µg of pTARGET/LC. Four-week-old hamsters received two doses of vaccine with different strategies and were challenged with 5 × DL₅₀Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130. The immune response generated by Lig chimera conferred 100% protection to hamsters treated with at least one dose of recombinant LC. Despite the high levels of antibodies that vaccinated animals produced, a sterilizing immunity was not achieved. The lack of a sterilizing immunity could indicate the importance of a mixed humoral and cellular immune response. The present study generated insights that will be useful in the future development of improved subunit vaccines against leptospirosis.

A One Health Approach to Investigating Leptospira Serogroups and Their Spatial Distributions among Humans and Animals in Rio Grande do Sul, Brazil, 2013⁻2015

Leptospirosis is an endemic zoonotic disease in Brazil and is widespread throughout rural populations in the state of Rio Grande do Sul. This study aimed to identify presumptive infecting Leptospira serogroups in human and animal cases and describe their occurrences within the ecoregions of the state by animal species. Data for human and animal leptospirosis cases were gathered from the government’s passive surveillance systems and presumptive infecting serogroups were identified based on a two-fold titer difference in serogroups in the microscopic agglutination test (MAT) panel. A total of 22 different serogroups were reported across both human and animal cases. Serogroup Icterohaemorrhagiae was the most common among humans, while serogroup Sejroe predominated among animal cases, particularly bovines. Each ecoregion had a large distribution of cases, with 51% of the human cases in the Parana–Paraiba ecoregion, and 81% of the animal cases in the Savannah ecoregion. Identifying and mapping the serogroups circulating using the One Health approach is the first step for further understanding the distribution of the disease in the state. This study has the potential to aid in guiding public health and agricultural practices, furthering the need for a human vaccine in high-risk populations to complement control and prevention efforts.

MAT cross-reactions or vaccine cross-protection: retrospective study of 863 leptospirosis canine cases

Dogs are naturally exposed to numerous pathogenic serogroups. Leptospirosis vaccines are claimed to afford a clinical protection restricted to the serogroups of which they are composed.

Objectives

Dogs exhibiting liver and kidney injury were suspected of having leptospirosis. The purpose of this study was to compare the microscopic agglutination test (MAT) results in naive and vaccinated dogs experiencing leptospirosis outcomes. Only MAT-positive animals were included in the study.

Methods

Over five years, 3 512 dogs were suspected of having leptospirosis. For each case, biochemical parameter results were recorded. Leptospirosis involvement was investigated by MAT performed against 6 major serogroups (Icterohaemorrhagiae, Canicola, Australis, Autumnalis, Grippotyphosa and Sejroë). MAT-positive results confirmed leptospirosis cases in 147 naïve dogs and in 580 fully vaccinated dogs. Serological titres of agglutinating antibodies were related to the severity of liver and kidney failure.

Results

The most prevalent outcome of leptospirosis in unvaccinated dogs was liver failure (57.8%) compared to 51.7% for kidney disease, but the most severe onset (90.8%) was found among the cases of acute kidney injury compared to the severe (42.3%) hepatitis cases. In dogs vaccinated by bivalent Icterohaemorrhagiae and Canicola bacterins, hepatitis decreased from 57.8 to 46.5% and acute kidney injury from 51.7 to 21.6%. The decrease was shown in leptospirosis cases induced by field strains belonging to the six most prevalent serogroups, including the 4 serogroups heterologous to the vaccine.

Conclusion

Common vaccination was efficient in decreasing hepatitis and kidney failure induced by field Leptospira spp infection regardless of the MAT-prominent serogroup and limited the disease severity in the remaining cases.

Advances & challenges in leptospiral vaccine development

Considerable progress has been made in the field of leptospiral vaccines development since its first use as a killed vaccine in guinea pigs. Despite the fact that the immunity conferred is restricted to serovars with closely related lipopolysaccharide antigen, certain vaccines have remained useful, especially in endemic regions, for the protection of high-risk individuals. Other conventional vaccines such as the live-attenuated vaccine and lipopolysaccharide (LPS) vaccine have not gained popularity due to the reactive response that follows their administration and the lack of understanding of the pathogenesis of leptospirosis. With the recent breakthrough and availability of complete genome sequences of Leptospira, development of novel vaccine including recombinant protein vaccine using reverse vaccinology approaches has yielded encouraging results. However, factors hindering the development of effective leptospiral vaccines include variation in serovar distribution from region to region, establishment of renal carrier status following vaccination and determination of the dose and endpoint titres acceptable as definitive indicators of protective immunity. In this review, advancements and progress made in LPS-based vaccines, killed- and live-attenuated vaccines, recombinant peptide vaccines and DNA vaccines against leptospirosis are highlighted.

Heterologous protection elicited by a live, attenuated, Leptospira vaccine

A previously-described live, attenuated vaccine (M1352, serovar Manilae, serogroup Pyrogenes) was tested in the hamster model of infection for cross-protective immunity. The vaccine elicited strong, significant cross-protection against lethal infection by strains representing four serologically distinct leptospiral serovars (Grippotyphosa, Australis, Canicola, and Autumnalis). Combined with our previously reported protection against serovars Pomona and Manilae, this work demonstrates unequivocal proof of concept for cross-protective immunity in leptospirosis.

LemA and Erp Y-like recombinant proteins from Leptospira interrogans protect hamsters from challenge using AddaVax™ as adjuvant

BACKGROUND

Recombinant subunit vaccines have been extensively evaluated as promising alternatives against leptospirosis. Here, we evaluated two proteins in formulations containing the adjuvant AddaVax™ as vaccine candidates for prevention and control of leptospirosis.

METHODS

Recombinant proteins rErp Y-like and rLemA were characterized by ELISA to assess their ability to bind extracellular matrix (ECM) components and fibrinogen. Groups of eight hamsters were immunized intramuscularly with rErp Y-like or rLemA mixed with a squalene-based adjuvant (AddaVax), and then vaccine efficacy was determined in terms of protection against a lethal challenge. The humoral immune response was determined by ELISA, and the evidence of sub-lethal infection was evaluated by histopathology and kidney culture.

RESULTS

rLemA protein binds laminin, fibrinogen, and collagen type IV, while rErp Y-like interacts with fibrinogen. Significant protection was achieved for rLemA and rErp Y-like vaccines, which showed 87.5% and 62.5% survivals, respectively. On day 28, the humoral immune response was significantly greater in the vaccine groups as compared to that in the control group, and the response was predominantly based on IgG2/3. The surviving animals showed negative results in culture isolation but presented with tissue lesions in the lungs and kidneys.

CONCLUSION

Cumulatively, our findings suggest that LemA and Erp Y-like proteins act as adhesins and are able to protect against mortality, but not against tissue lesions. Moreover, AddaVax is a novel adjuvant with potential for improving the immunogenicity of leptospiral vaccines.

A road map for leptospirosis research and health policies based on country needs in Latin America

This report summarizes the presentations, discussions and the recommendations coming from the Oswaldo Cruz Institute/FIOCRUZ International Workshop for Leptospirosis Research Based on Country Needs and the 5th Global Leptospirosis Environmental Action Network meeting, which was held in the city of Rio de Janeiro, Brazil, 10-12 November 2015. The event focused on health policy and worked to develop a road map as a consensus document to help guide decision-making by policymakers, funding bodies, and health care professionals. The direction that leptospirosis research should take in the coming years was emphasized, taking into account the needs of countries of Latin America, as well as experiences from other world regions, as provided by international experts. The operational concepts of "One Health" and translational research underlaid the discussions and the resulting recommendations. Despite the wide geographic distribution of leptospirosis and its impact in terms of incidence, morbidity, and mortality, leptospirosis is not yet considered a "tool-ready" disease for global initiatives. Surveillance programs need new tools and strategies for early detection, prevention, and follow-up. The major recommendations developed at the Rio meeting cover both health policy and research. The health policy recommendations should be taken into account by decisionmakers, government officials, and the Pan American Health Organization. The priorities for research, technological development, and innovation should be considered by research institutions, universities, and stakeholders.

Recent findings related to immune responses against leptospirosis and novel strategies to prevent infection

What are the new approaches and emerging ideas to prevent leptospirosis, a neglected bacterial re-emerging zoonotic disease? How do Leptospira interrogans escape the host defenses? We aim here to review and discuss the most recent literature that provides some answers to these questions, in particular data related to a better understanding of adaptive and innate immunity towards leptospires, and design of vaccines. This is an opinion paper, not a comprehensive review. We will try to highlight the new strategies and technologies boosting the search for drugs and vaccines. We will also address the bottlenecks and difficulties impairing the search for efficient vaccines and the many gaps in our knowledge of immunity against leptospirosis. Finally, we aim to delineate how Leptospira spp. escape the innate immune responses of Toll-Like receptors (TLR) and Nod-Like receptors (NLR). The rational use of TLR and NLR agonists as adjuvants could be key to design future vaccines against pathogenic leptospires.

Immunoprotective properties of recombinant LigA and LigB in a hamster model of acute leptospirosis

Leptospirosis is the most widespread zoonosis and is considered a major public health problem worldwide. Currently, there is no widely available vaccine against leptospirosis for use in humans. A purified, recombinant subunit vaccine that includes the last six immunoglobulin-like (Ig-like) domains of the leptospiral protein LigA (LigA7'-13) protects against lethal infection but not renal colonization after challenge by Leptospira interrogans. In this study, we examined whether the addition of the first seven Ig-like domains of LigB (LigB0-7) to LigA7'-13, can enhance immune protection and confer sterilizing immunity in the Golden Syrian hamster model of acute leptospirosis. Hamsters were subcutaneously immunized with soluble, recombinant LigA7'-13, LigB0-7, or a combination of LigA7'-13 and LigB0-7 in Freund's adjuvant. Immunization with Lig proteins generated a strong humoral immune response with high titers of IgG that recognized homologous protein, and cross-reacted with the heterologous protein as assessed by ELISA. LigA7'-13 alone, or in combination with LigB0-7, protected all hamsters from intraperitoneal challenge with a lethal dose of L. interrogans serovar Copenhageni strain Fiocruz L1-130. However, bacteria were recovered from the kidneys of all animals. Of eight animals immunized with LigB0-7, only three survived Leptospira challenge, one of which lacked renal colonization and had antibodies to native LigB by immunoblot. In addition, sera from two of the three LigB0-7 immunized survivors cross-reacted with LigA11-13, a region of LigA that is sufficient for protection. In summary, we confirmed that LigA7'-13 protects hamsters from death but not infection, and immunization with LigB0-7, either alone or in combination with LigA7'-13, did not confer sterilizing immunity.

A Universal Vaccine against Leptospirosis: Are We Going in the Right Direction?

Leptospirosis is the most widespread zoonosis in the world and a neglected tropical disease estimated to cause severe infection in more than one million people worldwide every year that can be combated by effective immunization. However, no significant progress has been made on the leptospirosis vaccine since the advent of bacterins over 100 years. Although protective against lethal infection, particularly in animals, bacterin-induced immunity is considered short term, serovar restricted, and the vaccine can cause serious side effects. The urgent need for a new vaccine has motivated several research groups to evaluate the protective immune response induced by recombinant vaccines. Significant protection has been reported with several promising outer membrane proteins, including LipL32 and the leptospiral immunoglobulin-like proteins. However, efficacy was variable and failed to induce a cross-protective response or sterile immunity among vaccinated animals. As hundreds of draft genomes of all known Leptospira species are now available, this should aid novel target discovery through reverse vaccinology (RV) and pangenomic studies. The identification of surface-exposed vaccine candidates that are highly conserved among infectious Leptospira spp. is a requirement for the development of a cross-protective universal vaccine. However, the lack of immune correlates is a major drawback to the application of RV to Leptospira genomes. In addition, as the protective immune response against leptospirosis is not fully understood, the rational use of adjuvants tends to be a process of trial and error. In this perspective, we discuss current advances, the pitfalls, and possible solutions for the development of a universal leptospirosis vaccine.

Distinct antibody responses of patients with mild and severe leptospirosis determined by whole proteome microarray analysis

BACKGROUND

Leptospirosis is an important zoonotic disease worldwide. Humans usually present a mild non-specific febrile illness, but a proportion of them develop more severe outcomes, such as multi-organ failure, lung hemorrhage and death. Such complications are thought to depend on several factors, including the host immunity. Protective immunity is associated with humoral immune response, but little is known about the immune response mounted during naturally-acquired Leptospira infection.

METHODS AND PRINCIPAL FINDINGS

Here, we used protein microarray chip to profile the antibody responses of patients with severe and mild leptospirosis against the complete Leptospira interrogans serovar Copenhageni predicted ORFeome. We discovered a limited number of immunodominant antigens, with 36 antigens specific to patients, of which 11 were potential serodiagnostic antigens, identified at acute phase, and 33 were potential subunit vaccine targets, detected after recovery. Moreover, we found distinct antibody profiles in patients with different clinical outcomes: in the severe group, overall IgM responses do not change and IgG responses increase over time, while both IgM and IgG responses remain stable in the mild patient group. Analyses of individual patients' responses showed that >74% of patients in the severe group had significant IgG increases over time compared to 29% of patients in the mild group. Additionally, 90% of IgM responses did not change over time in the mild group, compared to ~51% in the severe group.

CONCLUSIONS

In the present study, we detected antibody profiles associated with disease severity and speculate that patients with mild disease were protected from severe outcomes due to pre-existing antibodies, while patients with severe leptospirosis demonstrated an antibody profile typical of first exposure. Our findings represent a significant advance in the understanding of the humoral immune response to Leptospira infection, and we have identified new targets for the development of subunit vaccines and diagnostic tests.

Cathelicidin Insufficiency in Patients with Fatal Leptospirosis

Leptospirosis causes significant morbidity and mortality worldwide; however, the role of the host immune response in disease progression and high case fatality (>10-50%) is poorly understood. We conducted a multi-parameter investigation of patients with acute leptospirosis to identify mechanisms associated with case fatality. Whole blood transcriptional profiling of 16 hospitalized Brazilian patients with acute leptospirosis (13 survivors, 3 deceased) revealed fatal cases had lower expression of the antimicrobial peptide, cathelicidin, and chemokines, but more abundant pro-inflammatory cytokine receptors. In contrast, survivors generated strong adaptive immune signatures, including transcripts relevant to antigen presentation and immunoglobulin production. In an independent cohort (23 survivors, 22 deceased), fatal cases had higher bacterial loads (P = 0.0004) and lower anti-Leptospira antibody titers (P = 0.02) at the time of hospitalization, independent of the duration of illness. Low serum cathelicidin and RANTES levels during acute illness were independent risk factors for higher bacterial loads (P = 0.005) and death (P = 0.04), respectively. To investigate the mechanism of cathelicidin in patients surviving acute disease, we administered LL-37, the active peptide of cathelicidin, in a hamster model of lethal leptospirosis and found it significantly decreased bacterial loads and increased survival. Our findings indicate that the host immune response plays a central role in severe leptospirosis disease progression. While drawn from a limited study size, significant conclusions include that poor clinical outcomes are associated with high systemic bacterial loads, and a decreased antibody response. Furthermore, our data identified a key role for the antimicrobial peptide, cathelicidin, in mounting an effective bactericidal response against the pathogen, which represents a valuable new therapeutic approach for leptospirosis.

Vaccines against leptospirosis

Vaccines against leptospirosis followed within a year of the first isolation of Leptospira, with the first use of a killed whole cell bacterin vaccine in guinea pigs published in 1916. Since then, bacterin vaccines have been used in humans, cattle, swine, and dogs and remain the only vaccines licensed at the present time. The immunity elicited is restricted to serovars with related lipopolysaccharide (LPS) antigen. Likewise, vaccines based on LPS antigens have clearly demonstrated protection in animal models, which is also at best serogroup specific. The advent of leptospiral genome sequences has allowed a reverse vaccinology approach for vaccine development. However, the use of inadequate challenge doses and inappropriate statistical analysis invalidates many of the claims of protection with recombinant proteins.

The leptospiral outer membrane

The outer membrane (OM) is the front line of leptospiral interactions with their environment and the mammalian host. Unlike most invasive spirochetes, pathogenic leptospires must be able to survive in both free-living and host-adapted states. As organisms move from one set of environmental conditions to another, the OM must cope with a series of conflicting challenges. For example, the OM must be porous enough to allow nutrient uptake, yet robust enough to defend the cell against noxious substances. In the host, the OM presents a surface decorated with adhesins and receptors for attaching to, and acquiring, desirable host molecules such as the complement regulator, Factor H.Factor H. On the other hand, the OM must enable leptospires to evade detection by the host's immune system on their way from sites of invasion through the bloodstream to the protected niche of the proximal tubule. The picture that is emerging of the leptospiral OM is that, while it shares many of the characteristics of the OMs of spirochetes and Gram-negative bacteria, it is also unique and different in ways that make it of general interest to microbiologists. For example, unlike most other pathogenic spirochetes, the leptospiral OM is rich in lipopolysaccharide (LPS). Leptospiral LPS is similar to that of Gram-negative bacteria but has a number of unique structural features that may explain why it is not recognized by the LPS-specific Toll-like receptor 4 of humans. As in other spirochetes, lipoproteins are major components of the leptospiral OM, though their roles are poorly understood. The functions of transmembrane outer membrane proteins (OMPs) in many cases are better understood, thanks to homologies with their Gram-negative counterparts and the emergence of improved genetic techniques. This chapter will review recent discoveries involving the leptospiral OM and its role in leptospiral physiology and pathogenesis.

The molecular basis of leptospiral pathogenesis

The mechanisms of disease pathogenesis in leptospirosis are poorly defined. Recent developments in the application of genetic tools in the study of Leptospira have advanced our understanding by allowing the assessment of mutants in animal models. As a result, a small number of essential virulence factors have been identified, though most do not have a clearly defined function. Significant advances have also been made in the in vitro characterization of leptospiral interaction with host structures, including extracellular matrix proteins (such as laminin, elastin, fibronectin, collagens), proteins related to hemostasis (fibrinogen, plasmin), and soluble mediators of complement resistance (factor H, C4b-binding protein), although none of these in vitro findings has been translated to the host animal. Binding to host structures may permit colonization of the host, prevention of blood clotting may contribute to hemorrhage, while interaction with complement resistance mediators may contribute to survival in serum. While not a classical intracellular pathogen, the interaction of leptospires and phagocytic cells appears complex, with bacteria surviving uptake and promoting apoptosis; mutants relating to these processes (such as cell invasion and oxidative stress resistance) are attenuated in vivo. Another feature of leptospiral biology is the high degree of functional redundancy and the surprising lack of attenuation of mutants in what appear to be certain virulence factors, such as LipL32 and LigB. While many advances have been made, there remains a lack of understanding of how Leptospira causes tissue pathology. It is likely that leptospires have many novel pathogenesis mechanisms that are yet to be identified.

Host response to leptospira infection

Pathogenic Leptospira has the capacity to infect a broad range of mammalian hosts. Leptospirosis may appear as an acute, potentially fatal infection in accidental hosts, or progress into a chronic, largely asymptomatic infection in natural maintenance hosts. The course that Leptospira infection follows is dependent upon poorly understood factors, but is heavily influenced by both the host species and bacterial serovar involved in infection. Recognition of pathogen-associated molecular patterns (PAMPs) by a variety of host pattern recognition receptors (PRRs) activates the host immune system. The outcome of this response may result in bacterial clearance, limited bacterial colonization of a few target organs, principally the kidney, or induction of sepsis as the host succumbs to infection and dies. This chapter describes current knowledge of how the host recognizes Leptospira and responds to infection using innate and acquired immune responses. Aspects of immune-mediated pathology and pathogen strategies to evade the host immune response are also addressed.

Human leptospirosis: seroreactivity and genetic susceptibility in the population of São Miguel Island (Azores, Portugal)

Background

Leptospirosis is a worldwide zoonotic and recognized neglected infectious disease. It has been observed that only a proportion of individuals exposed to pathogenic species of Leptospira become infected and develop clinically evident disease. Moreover, little information is available in subsequent reinfections. In the present study, we determine if a first infection with leptospirosis protects against subsequent reinfection, and investigate which of the host genetic factors are involved in the susceptibility and resistance to leptospirosis.

Methodology and Findings

We conducted, in 2011, a retrospective hospital-based case-control study in the São Miguel Island population (Azores archipelago). In order to determine the seropositivity against pathogenic Leptospira after the first episode of leptospirosis, we performed a serological evaluation in 97 unrelated participants diagnosed with leptospirosis between 1992 and 2011. The results revealed that 46.4% of the 97 participants have circulating anti-Leptospira antibodies, and from these participants 35.6% maintained the seroprevalence for the same serogroup. Moreover, three of them were reinfected with unrelated Leptospira serovars. The genetic study was carried out by adding a control group composed of 470 unrelated healthy blood donors, also from São Miguel Island. Twenty five SNPs among twelve innate immune genes – IL1α, IL1β, IL6, IL10, IL12RB1, TLR2, TLR4, TLR9, CD14, CISH, LTA and TNF – were genotyped, as well as HLA class I (–A and –B) genes. Association analysis indicates that genotypes -511GG (OR = 1.6, 95%CI 1.01-2.56, p = 0.04) in IL1β, +1196CG (OR = 2.0, 95%CI 1.26-3.27, p = 0.003) in IL12RB1, -292TA (OR = 1.8, 95% CI 1.06–2.1, p = 0.03) and +3415CG (OR = 1.8, 95% CI 1.08–3.08, p = 0.02), both in CISH confer susceptibility to pathogenic Leptospira.

Conclusion

The present study suggests some degree of long-term protection against leptospires with an attenuation of symptoms in case of reinfection. Moreover, our data supports the genetic influence of IL1β, IL12RB1 and CISH genes and the susceptibility to leptospirosis infection.

Pushing the Bacterial Envelope

Over the past three decades, a powerful array of techniques has been developed for expressing heterologous proteins and saccharides on the surface of bacteria. Surface-engineered bacteria, in turn, have proven useful in a variety of settings, including high-throughput screening, biofuel production, and vaccinology. In this chapter, we provide a comprehensive review of methods for displaying polypeptides and sugars on the bacterial cell surface, and discuss the many innovative applications these methods have found to date. While already an important biotechnological tool, we believe bacterial surface display may be further improved through integration with emerging methodology in other fields, such as protein engineering and synthetic chemistry. Ultimately, we envision bacterial display becoming a multidisciplinary platform with the potential to transform basic and applied research in bacteriology, biotechnology, and biomedicine.

Leptospiral outer membrane protein LipL41 is not essential for acute leptospirosis but requires a small chaperone protein, lep, for stable expression

Leptospirosis is a worldwide zoonosis caused by pathogenic Leptospira spp., but knowledge of leptospiral pathogenesis remains limited. However, the development of mutagenesis systems has allowed the investigation of putative virulence factors and their involvement in leptospirosis. LipL41 is the third most abundant lipoprotein found in the outer membranes of pathogenic leptospires and has been considered a putative virulence factor. LipL41 is encoded on the large chromosome 28 bp upstream of a small open reading frame encoding a hypothetical protein of unknown function. This gene was named lep, for LipL41 expression partner. In this study, lipL41 was found to be cotranscribed with lep. Two transposon mutants were characterized: a lipL41 mutant and a lep mutant. In the lep mutant, LipL41 protein levels were reduced by approximately 90%. Lep was shown through cross-linking and coexpression experiments to bind to LipL41. Lep is proposed to be a molecular chaperone essential for the stable expression of LipL41. The roles of LipL41 and Lep in the pathogenesis of Leptospira interrogans were investigated; surprisingly, neither of these two unique proteins was essential for acute leptospirosis.

Evaluation of 238 antigens of Leptospira borgpetersenii serovar Hardjo for protection against kidney colonisation

Leptospirosis is a zoonotic disease affecting animals and humans worldwide. Leptospiral infection in cattle can cause reproductive failure and reduced weight gain, and importantly, infection represents a significant disease risk for farmers. Current bacterin vaccines offer protection that is short-lived and restricted at best to related serovars. The development of protective vaccines that stimulate immunity across multiple leptospiral serovars would therefore be advantageous. This study used a reverse vaccinology approach to evaluate a set of Leptospira borgpetersenii proteins in the hamster infection model. The L. borgpetersenii serovar Hardjo strain L550 genome sequence was analysed and genes encoding 262 predicted outer membrane or secreted proteins were selected. From this list, 238 proteins or protein fragments were successfully expressed and purified; 28 proteins (12%) were soluble, while the remaining 210 proteins (88%) were insoluble and purified under denaturing conditions. Proteins were mixed into 48 pools of up to five each and tested for protection against infection as assessed by renal colonisation in the hamster model of infection. None of the pools of antigens protected the hamsters against infection, despite a detectable antibody response being mounted against the majority of proteins (71%). This study is the first large scale evaluation of individual leptospiral proteins for ability to induce a protective immune response in the hamster infection model. It thus constitutes an important reference of protein immunogenicity and non-protective antigens that should be consulted before embarking on any future subunit vaccine experiments.

Leptospirosis-persistence of a dilemma: an overview with particular emphasis on trends and recent advances in vaccines and vaccination strategies

Leptospirosis, caused by pathogenic spirochetes of the genus Leptospira, affects both humans and animals and is among the most common but neglected direct zoonotic disease in the world, particularly in untreated or undiagnosed animals as well as humans. Now, it has been considered as a re-emerging disease causing global health problem due to its increasing incidences in developing as well as developed nations. It is a multisystemic disease leading to death. Diagnostic tests of importance are Latex Agglutination Test (LAT), lateral flow and immunoglobulin M (IgM) based ELISA, PCR based assays, Multiple-microscopic Agglutination Test (MAT), Loop-mediated Isothermal Amplification (LAMP) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Molecular tools like PCR-RFLP, real-time PCR, multiplex PCR, qPCR and immunocapture PCR have all been found useful for rapid and confirmatory detection and differentiation of pathogenic and non-pathogenic leptospires. Inactivated/killed and attenuated vaccines are always attempted, since the beginning of vaccine and vaccination story, against all emerging pathogens with mixed success stories. The advanced tools and techniques like recombinant DNA technology, reverse genetics, DNA vaccination, molecular genetics and proteomics approaches are being explored for search of novel antigens, proteins and genes as potential candidates to discover safer, efficient and better vaccines for leptospirosis. The present review highlights the leptospirosis, susceptible population, disease transmission and epidemiology, treatment, trends and advances in diagnosis, vaccines and vaccination strategies in humans and animals with a view to combat this organism having public health significance.

Analysis of multiple Leptospira interrogans serovar Canicola vaccine proteomes and identification of LipL32 as a biomarker for potency

The current batch potency test for Leptospira interrogans serovar Canicola vaccines requires the use of a large number of hamsters and has severe effects (i.e., hepatic and renal failure resulting in death); while this vaccine is effective, a safer, cheaper, more ethical replacement is desired. The aim of this study was to analyze vaccine proteomes and identify target molecules common to all L. interrogans serovar Canicola vaccines which could be used to design an in vitro potency test. Initial analysis of L. interrogans serovar Canicola vaccines (A to E) from different manufacturers, using the Limulus amebocyte lysate assay and silver-stained sodium dodecyl sulfate polyacrylamide gels, indicated that lipopolysaccharide was not present in all vaccines, preventing it from being a suitable target molecule. The protein contents of vaccines A to E were therefore determined by two-dimensional liquid chromatography mass spectrometry ([2D-LC/MS] 221 ± 31, 9 ± 8, 34 ± 4, 21 ± 5, and 34 ± 17 proteins [mean ± 1 standard deviation] found, respectively). The outer membrane protein LipL32 was established to be common to all and to be present at a significantly higher (P ≤ 0.05) relative spectral abundance in a batch of vaccine which passed the in vivo potency test than in one which had failed. Further analysis using multiple reaction monitoring revealed that the concentration of the N terminus of LipL32 was significantly lower (P ≤ 0.01) in failed batches (n = 2) of vaccine than in passed batches (n = 2); the concentration of the C terminus between the two batches was approximately the same. An in vitro Leptospira vaccine potency test, based on N-terminal amino acid quantification of LipL32, was subsequently developed.

Evaluation of novel fusion proteins derived from extracellular matrix binding domains of LigB as vaccine candidates against leptospirosis in a hamster model

Leptospira binds to host extracellular matrix (ECM) through surface exposed outer membrane proteins called adhesin in order to initiate infection. Of various adhesins present on the surface of the spirochete, Leptospira-immunoglobulin like proteins (Lig proteins) and LipL32 are most abundant, widely distributed among pathogenic serovars and well characterized. Various fragments of Lig proteins (Ligcon4, Ligcon4-7.5, LigBcen2) and C-terminus fragment of LipL32 all of that bind to host ECM were fused, expressed and purified in soluble form as fusion proteins. Four week hamsters were immunized subcutaneously with various fusion proteins emulsified in EMULSIGEN-D adjuvant and subsequently boosted at 3 weeks. The protective efficacy of these novel fusion proteins was evaluated against subsequent challenge with highly virulent L. interrogans serovar Pomona (MLD50-100). Our results indicate that fusion protein based vaccine induced significant protection against acute infection with respect to PBS-adjuvant vaccinated controls as revealed by enhanced survival and reduced pulmonary hemorrhage. Moreover, the protection mediated by these novel proteins was higher than that of conserved region of Lig protein (Ligcon, established protective antigen) and correlated to the level of antibodies. LipL32 failed to impart significant protection, however fusing its immunogenic C-terminus domain to Lig fragments slightly delayed the morbidity of the infected animals. Our results demonstrate that this novel strategy could be promising in developing effective subunit vaccine to combat this zoonotic infection.

Pathogenesis of leptospirosis: the influence of genomics

Leptospirosis is the most widespread zoonosis worldwide and is caused by serovars of pathogenic Leptospira species. The understanding of leptospiral pathogenesis lags far behind that of many other bacterial pathogens. Current research is thus directed at identification of leptospiral virulence factors. Saprophytic Leptospira species are environmental organisms that never cause disease. Comparative genomics of pathogens and saprophytes has allowed the identification of more than 900 genes unique to either Leptospira interrogans or Leptospira borgpetersenii; these genes potentially encode virulence-associated proteins. However, genes of unknown function are over-represented in this subset of pathogen-specific genes, accounting for 80% and 60% of open reading frames, respectively. This finding, together with the absence of virulence factor homologues among the proteins of known function, suggests that Leptospira possesses unique virulence mechanisms. Whole genome microarray studies have identified genes whose expression is differentially regulated under a range of simulated in vivo conditions, such as physiological temperature and osmolarity, low iron levels, and the presence of serum. The subset of genes identified by these studies is likely to include virulence factors. However, most such genes encode proteins of unknown function, consistent with the hypothesis that leptospiral virulence genes do not have homologues in other bacterial species. The recent development of mutagenesis systems for pathogenic Leptospira spp. has allowed the screening of defined mutants for attenuation of virulence in animal infection models and has identified definitively for the first time a range of virulence factors, including lipopolysaccharide, flagella, heme oxygenase, and the OmpA-family protein, Loa22. Interestingly, inactivation of a number of genes hypothesised to encode virulence factors based on in vitro virulence-associated properties did not result in attenuation of virulence, suggesting a degree of functional redundancy in leptospiral pathogenic mechanisms.