Leptospira interrogans is the major causative agent of leptospirosis. Humans, canines and livestock animals are susceptible to Leptospira species and can develop fulminant disease. Rodents serve as reservoir hosts in which the bacteria colonize the renal tubules and are excreted in the urine. The host immune response to Leptospira spp. remains poorly defined. We show that L. interrogans induces a robust type I interferon (IFN) response in human and murine macrophages that is dependent on the cytosolic dsDNA sensor Cyclic GMP-AMP Synthase (cGAS) and the Stimulator of IFN Genes (STING) signaling pathway. Further, we show that mice deficient in the IFNα/β receptor subunit 1 (IFNAR1) or STING had higher bacterial burdens and increased renal colonization following infection in vivo suggesting that cGAS-STING-driven type I IFN is required for the host defense against L. interrogans. These findings demonstrate the significance of cGAS-STING- dependent type I IFN signaling in mammalian innate immune responses to L. interrogans.

Leptospirosis is a globally distributed zoonotic disease transmitted from animal reservoirs to humans. It is particularly common in tropical regions of Africa, Asia, and Central and South America during heavy rainfall when bacterial spirochetes are released from soil into areas of flooding. Despite causing >1 million severe cases, 58 900 deaths, and 2.9 million disability-adjusted life-years annually-exceeding established neglected tropical diseases-leptospirosis remains underrecognized as a neglected tropical disease. It affects occupational groups like farmers due to high prevalence in livestock and is spread by rodents in urban settings that have poor sanitation and infrastructure. Although effectively treated with inexpensive antibiotics, neglect of leptospirosis research and development has led to a lack of awareness and unavailability of preventive and diagnostic approaches. This review covers the geographic prevalence, disproportionate impacts on marginalized communities, and opportunities for improving social, economic, and healthcare burdens for patients with leptospirosis.

Background: Severe pulmonary hemorrhagic syndrome (SPHS) remains a fatal complication of leptospirosis with poorly understood mechanisms and an urgent need for effective biomarkers. Methods: A nested case-control analysis was conducted using blood specimens from two previous Thai leptospirosis cohorts. Candidate microRNAs were initially discovered through a global profiling of 798 serum microRNAs in five SPHS and seven non-SPHS patients, and then validated using real-time polymerase chain reactions in 168 patients. Pathways enriched from microRNA targets were compared to those from an integrated transcriptomic-proteomic analysis. Proteins pertaining to the key resulting pathway were measured to validate significance and reveal correlation with microRNA biomarkers. Results: Serum microRNA profiling revealed a total of 81 significantly expressed microRNAs, of which seven were selected for further validation in the whole cohort of 168 leptospirosis patients, including 28 in SPHS and 140 nonSPHS groups. Among the selected microRNAs, miR-5010-3p and miR-147b-3p had significantly higher expression in SPHS group compared to nonSPHS group, with consistently higher expression after adjusting for age, sex, days of illness, comorbidity, smoking status or recruitment site. The two had area under the curve (AUC) values of 0.76 (95% CI: 0.67-0.85) and 0.70 (95% CI: 0.56-0.81) for discriminating SPHS, respectively. These microRNAs also exhibited consistent AUC values in patients tested before chest radiograph shadows manifested. Combination of miR-5010-3p with miR-548ai and miR-224-5p, as selected by Bayesian Model Averaging algorithm, substantially boosts the AUC value to 0.86 (95% CI: 0.77-0.94). The miRNA biomarkers also enhanced the predictive values of a previously validated clinical model, increasing AUC value from 0.87 to 0.92 with a significant reclassification net index. Multi-omics pathway analysis incorporating microRNA targets and transcriptomic-proteomic data suggested TNF signaling as among the key pathways. In validation, seven out of ten pathway proteins were significantly different between groups, with principal components correlated with severity and miR-5010-3p. Conclusions: MiR-5010-3p and miR-147b-3p are novel biomarkers with good predictability and potential relevance with TNF signaling pathway, an important host response mechanism in leptospirosis SPHS. (c) 2025 The Authors. Published by Elsevier Ltd on behalf of The British Infection Association. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Leptospira interrogans is the major causative agent of leptospirosis. Rodents are considered the most important reservoir of Leptospira. Infected rodents are asymptomatic carriers in which bacteria colonize the kidneys and are shed in the urine. Leptospira also infects a variety of other mammals including humans. Humans are incidental hosts but can develop fulminant disease which can prove fatal. The immune response to Leptospira spp. remains poorly defined. Leptospira can induce an IL-1β response via NLRP3 inflammasome activation. However, compared to other bacteria, L. interrogans triggers a relatively weak IL-1β response in mouse macrophages. In contrast, L. interrogans induces a robust IL-1β response in human monocytes. To investigate this, we utilized a mouse model with a mutation in NLRP3, associated with human cryopyrin-associated periodic syndrome, which results in NLRP3 hyperactivation. We observed a pronounced IL-1β response in NLRP3A350V/+ mouse macrophages upon infection with L. interrogans. An intraperitoneal infection of NLRP3A350V/+ mice with L. interrogans also resulted in increased mortality compared to wild-type mice. Moreover, a subcutaneous infection of NLRP3A350V/+ mice resulted in diminished kidney colonization, suggesting that a robust NLRP3 response may limit bacterial persistence in the kidney. These findings offer insights into why rodents serve as reservoir hosts for L. interrogans, while humans are more susceptible to severe disease. Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)

Abstract Leptospirosis is an emerging zoonotic disease, predominant in tropical and sub-tropical climates, with increasing sporadic outbreaks worldwide causing around 60,000 deaths per year. The spirochetal bacteria Leptospira interrogans is the major causative agent of leptospirosis. Canines and livestock animals are particularly susceptible to Leptospira and develop acute symptoms. Rodents, on the other hand, serve as reservoir hosts in which the bacteria chronically colonize the kidneys and get excreted in the urine. Humans are incidental hosts but can develop fulminant disease which can prove fatal. The host immune response to Leptospira spp. remains poorly defined. Leptospiral lipopolysaccharide and lipoproteins can activate TLR4 and TLR2. In addition, leptospires have been shown to activate the NLRP3 inflammasome. However, we observed that L. interrogans induced a poor inflammasome response particularly in mouse macrophages when compared to other bacteria known to activate NLRP3 inflammasome. In contrast, L. interrogans induced robust type I IFN responses in both mouse macrophages and human monocytes. In vivo studies suggest a potential role of type I IFN response in controlling bacteria loads in mouse models. Interestingly, we found the type I IFN response to be dependent on both cGAS-STING and TLR4-TRIF pathways. Further, differences in disease susceptibility in mouse and humans, when infected with Leptospira, may be explained by differences in host-specific immune responses.

Leptospirosis, the most widespread zoonotic disease in the world, is broadly understudied in multi-host wildlife systems. Knowledge gaps regarding Leptospira circulation in wildlife, particularly in densely populated areas, contribute to frequent misdiagnoses in humans and domestic animals. We assessed Leptospira prevalence levels and risk factors in five target wildlife species across the greater Los Angeles region: striped skunks (Mephitis mephitis), raccoons (Procyon lotor), coyotes (Canis latrans), Virginia opossums (Didelphis virginiana), and fox squirrels (Sciurus niger). We sampled more than 960 individual animals, including over 700 from target species in the greater Los Angeles region, and an additional 266 sampled opportunistically from other California regions and species. In the five target species seroprevalences ranged from 5 to 60%, and infection prevalences ranged from 0.8 to 15.2% in all except fox squirrels (0%). Leptospira phylogenomics and patterns of serologic reactivity suggest that mainland terrestrial wildlife, particularly mesocarnivores, could be the source of repeated observed introductions of Leptospira into local marine and island ecosystems. Overall, we found evidence of widespread Leptospira exposure in wildlife across Los Angeles and surrounding regions. This indicates exposure risk for humans and domestic animals and highlights that this pathogen can circulate endemically in many wildlife species even in densely populated urban areas.

Leptospirosis is a quintessential one health disease of humans and animals caused by pathogenic spirochetes of the genus Leptospira. Intra- and interspecies transmission is dependent on 1) reservoir host animals in which organisms replicate and are shed in urine over long periods of time, 2) the persistence of spirochetes in the environment, and 3) subsequent human-animal-environmental interactions. The combination of increased flooding events due to climate change, changes in human-animal-environmental interactions as a result of the pandemic that favor a rise in the incidence of leptospirosis, and under-recognition of leptospirosis because of nonspecific clinical signs and severe signs that resemble COVID-19 represents a "perfect storm" for resurgence of leptospirosis in people and domestic animals. Although often considered a disease that occurs in warm, humid climates with high annual rainfall, pathogenic Leptospira spp have recently been associated with disease in animals and humans that reside in semiarid regions like the southwestern US and have impacted humans that have a wide spectrum of socioeconomic backgrounds. Therefore, it is critical that physicians, veterinarians, and public health experts maintain a high index of suspicion for the disease regardless of geographic and socioeconomic circumstances and work together to understand outbreaks and implement appropriate control measures. Over the last decade, major strides have been made in our understanding of the disease because of improvements in diagnostic tests, molecular epidemiologic tools, educational efforts on preventive measures, and vaccines. These novel approaches are highlighted in the companion Currents in One Health by Sykes et al, AJVR, September 2022.

Leptospirosis is an archetypal One Health problem as described in the companion Currents in One Health article in the October 2022 issue of the Journal of the American Veterinary Medical Association by Sykes et al. A thorough understanding of leptospirosis requires a detailed analysis of the elaborate interplay among pathogenic leptospiral strains, host species, and the environment. Such an understanding is required to inform appropriate preventative measures including vaccine design, prophylaxis efforts, educational programs that help to reduce exposure to pathogenic spirochetes, as well as policy development. Because of the complex epidemiology of leptospirosis, a One Health approach as defined by the One Health Initiative Task Force is critical-an approach that calls for "the collaborative efforts of multiple disciplines working locally, nationally, and globally, to attain optimal health for people, animals and our environment." Over the last three decades, progressive advances in cutting-edge molecular typing techniques, as well as our ability to rapidly generate and share large amounts of sequence data through establishment and growth of databases, have been central to accelerating a One Health understanding of the epidemiology of leptospirosis. Nevertheless, our dependence on serotype information because of the serovar-specific nature of current vaccines means that laborious serotyping efforts continue. With the advent of new approaches such as mRNA vaccines that are based on lipopolysaccharide immunogens, sequence- and/or proteomics-based typing methods may replace these methods.

A One Health approach to the epidemiology, management, surveillance, and control of leptospirosis relies on accessible and accurate diagnostics that can be applied to humans and companion animals and livestock. Diagnosis should be multifaceted and take into account exposure risk, clinical presentation, and multiple direct and/or indirect diagnostic approaches. Methods of direct detection of Leptospira spp. include culture, histopathology and immunostaining of tissues or clinical specimens, and nucleic acid amplification tests (NAATs). Indirect serologic methods to detect leptospiral antibodies include the microscopic agglutination test (MAT), the enzyme-linked immunosorbent assay (ELISA), and lateral flow methods. Rapid diagnostics that can be applied at the point-of-care; NAAT and lateral flow serologic tests are essential for management of acute infection and control of outbreaks. Culture is essential to an understanding of regional knowledge of circulating strains, and we discuss recent improvements in methods for cultivation, genomic sequencing, and serotyping. We review the limitations of NAATs, MAT, and other diagnostic approaches in the context of our expanding understanding of the diversity of pathogenic Leptospira spp. Novel approaches are needed, such as loop mediated isothermal amplification (LAMP) and clustered regularly interspaced short palindromic repeats (CRISPR)-based approaches to leptospiral nucleic acid detection.

Leptospirosis is a widespread zoonotic disease which can be potentially fatal in infected humans and dogs. The spirochetal bacteria Leptospira interrogans is the major causative agent of leptospirosis. Rodents serve as reservoir hosts for L. interrogans and once colonized they continue to shed bacteria in their urine. The host immune response to Leptospira spp. remains poorly defined. Leptospiral lipopolysaccharide and lipoproteins can activate TLR4 and TLR2. In addition, leptospires have been shown to activate the NLRP3 inflammasome in macrophages. We observed that when compared to other Gram-negative bacteria, L. interrogans induced a poor inflammasome response with little or no notable pyroptosis. In contrast, L. interrogans induced a robust type I IFN responses in both mouse macrophages and human monocytes. The L. interrogans-induced type I IFN response was dependent on both cGAS and STING and resulted in rapid phosphorylation of TBK1 and IRF3. Furthermore, supernatants from infected macrophages were capable of inducing IFNβ expression in uninfected macrophages, suggesting paracrine signaling from infected cells. These studies demonstrate that L. interrogans can drive a cGAS-STING dependent type I IFN response that may contribute to the host defense against this pathogen.

1 Medical College of Wisconsin, Milwaukee, Wisconsin, United States of America, 2 Pasteur Institute, Paris, France, 3 Duke University Medical Center, Durham, North Carolina, United States of America, 4 Durham VA Medical Center, Durham, North Carolina, United States of America, 5 VA Greater Los Angeles Healthcare System, Los Angeles, California, United States of America, 6 The David Geffen School of Medicine at the University of California, Los Angeles, California, United States of America

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.

Leptospirosis is a globally widespread spirochetal infection spread from animals to humans. Infections are common in settings of endemicity, primarily in tropical regions of the world. Leptospirosis is typically a self-limited febrile illness but may progress to potentially fatal multiorgan system failure. Patients often present with a nonspecific acute febrile illness that is clinically difficult to distinguish from other similarly presenting infections endemic to tropical regions, including dengue fever, influenza, and malaria. A high index of suspicion is essential to early identification of patients who may benefit from antimicrobial therapy. Diagnostic testing is key to both recognition of early infection and outbreak investigation, typically in the setting of water exposure after heavy rainfall and flooding. This review focuses on the epidemiology, clinical manifestations, and laboratory diagnosis of leptospirosis, including nucleic acid amplification tests, culture, direct detection, and serological approaches.

Urinary tract infections (UTIs) are among the most common bacterial infections in the United States and are a major driver of antibiotic use, both appropriate and inappropriate, across healthcare settings. Novel UTI diagnostics are a strategy that might enable better UTI treatment. Members of the Antibacterial Resistance Leadership Group Laboratory Center and the Infectious Diseases Society of America Diagnostics Committee convened to envision ideal future UTI diagnostics, with a view towards improving delivery of healthcare, patient outcomes and experiences, and antibiotic use, addressing which types of UTI diagnostics are needed and how companies might approach development of novel UTI diagnostics.

The wide variety of pathogenic Leptospira serovars and the weak protection offered by the available vaccines encourage the search for protective immunogens against leptospirosis. We found that the secretin GspD of the type II secretion system (T2S) of Leptospira interrogans serovar Canicola was highly conserved amongst pathogenic serovars and was expressed in vivo during infection, as shown by immunohistochemistry. Convalescent sera of hamsters, dogs, and cows showed the presence of IgG antibodies, recognizing a recombinant version of this protein expressed in Escherichia coli (rGspDLC) in Western blot assays. In a pilot vaccination study, a group of eight hamsters was immunized on days zero and 14 with 50 µg of rGspDLC mixed with Freund’s incomplete adjuvant (FIA). On day 28 of the study, 1,000 LD50 (Lethal Dose 50%) of a virulent strain of Leptospira interrogans serovar Canicola (LOCaS46) were inoculated by an intraoral submucosal route (IOSM). Seventy-five percent protection against disease (p = 0.017573, Fisher’s exact test) and 50% protection against infection were observed in this group of vaccinated hamsters. In contrast, 85% of non-vaccinated hamsters died six to nine days after the challenge. These results suggest the potential usefulness of the T2S secretin GspD of Leptospira as a protective recombinant vaccine against leptospirosis.

Bloodstream infections are a leading cause of morbidity and mortality. Molecular rapid diagnostic tests (mRDTs) are transforming care for patients with bloodstream infection by providing the opportunity to dramatically shorten times to effective therapy and speeding de-escalation of overly broad empiric therapy. However, because of the novelty of these tests which provide information regarding microbial identification and whether specific antibiotic-resistance mutations were detected, many front-line providers still delay final decisions until complete phenotypic susceptibility results are available several days later. Thus the benefits of mRDTs have been largely limited to circumstances where antimicrobial stewardship programs closely monitor these tests and intervene as soon as the results are available. We searched PubMed and Google Scholar for articles published from 1980 to 2019 using the terms antibiotic, antifungal, bacteremia, bloodstream infection, candidemia, candidiasis, children, coagulase negative staphylococcus, consultation, contamination, costs, echocardiogram, endocarditis, enterobacteriaceae, enterococcus, Gram-negative, guidelines, IDSA, immunocompromised, infectious disease or ID, lumbar puncture, meningitis, mortality, MRSA, MSSA, neonatal, outcomes, pediatric, pneumococcal, polymicrobial, Pseudomonas, rapid diagnostic testing, resistance, risk factors, sepsis, Staphylococcus aureus, stewardship, streptococcus, and treatment. With the data from this search, we aim to provide guidance to front-line providers regarding the interpretation and immediate actions to be taken in response to the identification of common bloodstream pathogens by mRDTs. In addition to antimicrobial therapy, additional diagnostic or therapeutic interventions are recommended for particular organisms and clinical settings to either determine the extent of infection or control its source. Pediatric perspectives are offered for those bloodstream pathogens for which management differs from that in adults.

Background The syphilis epidemic continues to cause substantial morbidity and mortality worldwide, particularly in low- and middle-income countries, despite several recent disease control initiatives. Though our understanding of the pathogenesis of this disease and the biology of the syphilis agent, Treponema pallidum subsp. pallidum has improved over the last two decades, further research is necessary to improve clinical diagnosis and disease management protocols. Additionally, such research efforts could contribute to the identification of possible targets for the development of an effective vaccine to stem syphilis spread. Methods This study will recruit two cohorts of participants with active syphilis infection, one with de novo infection, one with repeat infection. Whole blood specimens will be collected from each study participant at baseline, 4, 12, 24, 36, and 48 weeks, to track specific markers of their immunological response, as well as to compare humoral reactivity to Treponema pallidum antigens between the two groups. Additionally, we will use serum specimens to look for unique cytokine patterns in participants with early syphilis. Oral and blood samples, as well as samples from any syphilitic lesions present, will also be collected to sequence any Treponema pallidum DNA found. Discussion By furthering our understanding of syphilis pathogenesis and human host immune response to Treponema pallidum , we will provide important data that will help in development of new point-of-care tests that could better identify active infection, leading to improved syphilis diagnosis and management. Findings could also contribute to vaccine development efforts.