Correlation between renal distribution of leptospires during the acute phase and chronic renal dysfunction in a hamster model of infection with Leptospira interrogans

Leptospirosis: A dual threat - predisposing risk for renal transplant and trigger for renal transplant dysfunction

Leptospirosis (LTPS) is a bacterial infection that affects humans, often with mild or no symptoms. It is estimated that approximately 10 % of patients with LTPS may experience multi-organ dysfunction, including renal abnormalities. In regions where LTPS is widespread, a considerable number of instances involving acute kidney injury (AKI) and chronic kidney disease (CKD) of unknown etiology (CKDu) have been reported. Additionally, studies have shown a correlation between kidney graft dysfunction in patients with stable kidney transplants after LTPS. These findings indicate that exposure to LTPS may increase the likelihood of kidney transplantation due to the onset of both acute and chronic kidney injuries. Simultaneously, it poses a potential risk to the stability of kidney grafts. Unfortunately, there is limited scientific literature addressing this issue, making it difficult to determine the negative impact that LTPS may have, such as its role as a risk factor for the need of kidney transplantation or as a threat to individuals who have undergone kidney transplants. This study aims to shed light on the immune mechanisms triggered during LTPS infection and their importance in both kidney damage and allograft dysfunction.

Neutralizing gut-derived lipopolysaccharide as a novel therapeutic strategy for severe leptospirosis

Leptospirosis is an emerging infectious disease caused by pathogenic Leptospira spp. Humans and some mammals can develop severe forms of leptospirosis accompanied by a dysregulated inflammatory response, which often results in death. The gut microbiota has been increasingly recognized as a vital element in systemic health. However, the precise role of the gut microbiota in severe leptospirosis is still unknown. Here, we aimed to explore the function and potential mechanisms of the gut microbiota in a hamster model of severe leptospirosis. Our study showed that leptospires were able to multiply in the intestine, cause pathological injury, and induce intestinal and systemic inflammatory responses. 16S rRNA gene sequencing analysis revealed that Leptospira infection changed the composition of the gut microbiota of hamsters with an expansion of Proteobacteria. In addition, gut barrier permeability was increased after infection, as reflected by a decrease in the expression of tight junctions. Translocated Proteobacteria were found in the intestinal epithelium of moribund hamsters, as determined by fluorescence in situ hybridization, with elevated lipopolysaccharide (LPS) levels in the serum. Moreover, gut microbiota depletion reduced the survival time, increased the leptospiral load, and promoted the expression of proinflammatory cytokines after Leptospira infection. Intriguingly, fecal filtration and serum from moribund hamsters both increased the transcription of TNF-α, IL-1β, IL-10, and TLR4 in macrophages compared with those from uninfected hamsters. These stimulating activities were inhibited by LPS neutralization using polymyxin B. Based on our findings, we identified an LPS neutralization therapy that significantly improved the survival rates in severe leptospirosis when used in combination with antibiotic therapy or polyclonal antibody therapy. In conclusion, our study not only uncovers the role of the gut microbiota in severe leptospirosis but also provides a therapeutic strategy for severe leptospirosis.

Non-purulent myositis caused by direct invasion of skeletal muscle tissue by Leptospira in a hamster model

Myalgia is a common symptom of Leptospira infection in humans. Autopsies have reported that muscle tissue shows degeneration and necrosis of the myofibers and infiltration of inflammatory cells composed mainly of macrophages and lymphocytes. It remains unclear whether Leptospira directly infects the muscle and how the infiltrating inflammatory cells are involved in muscle fiber destruction. This study evaluated the relationship between histopathological changes and leptospiral localization in the muscle tissue of a hamster model. The influence of macrophages in skeletal muscle injury was also investigated, using selective depletion of macrophages by administration of liposomal clodronate. Hamsters infected subcutaneously with Leptospira interrogans serovar Manilae strain UP-MMC-SM showed myositis of the thighs adjacent to the inoculated area beginning at 6 days post-infection. The myositis was non-purulent and showed sporadic degeneration and necrosis of muscle fibers. The degeneration of myofibers was accompanied by aggregations of macrophages. Immunofluorescence staining revealed leptospires surrounding the damaged muscle fibers. Subcutaneous injection of formalin-killed Leptospira or intraperitoneal injection of live Leptospira caused no myositis in hamster thighs. Liposomal clodronate treatment in infected hamsters reduced macrophage infiltration in muscle tissue without impacting bacterial clearance. Muscle necrosis was still observed in the infected hamsters treated with liposomal clodronate, and there was no significant change in serum creatine kinase levels compared to those in animals treated with liposomes alone. Our findings suggest that leptospiral invasion of muscle tissue from an inoculation site leads to the destruction of muscle fibers and causes non-purulent myositis, whereas the infiltrating macrophages contribute less to muscle destruction.

Dissemination of Leptospira into the intestinal tract resulting in fecal excretion in a hamster model of subcutaneous infection with Leptospirainterrogans

Leptospirosis, caused by pathogenic Leptospira, is one of the most common zoonotic diseases in the world. It is transmitted to humans through the skin and mucous membranes by contact with water or soil contaminated with urine excreted from infected animals. In human infections, gastrointestinal symptoms such as abdominal pain, vomiting, and diarrhea have been frequently observed, but there have been no reports analyzing gastrointestinal lesions in leptospirosis, and the pathological mechanism of gastrointestinal symptoms in leptospirosis remains unclear. In this study, we investigated the pathological changes and the distribution of leptospires in the intestinal wall, and the presence of leptospires in the intestinal contents and feces, of hamsters subcutaneously infected with Leptospira interrogans. Results showed that infected hamsters had macroscopic redness in the jejunum and ileum. Submucosal hemorrhage was observed histologically, and there was no infiltration of inflammatory cells such as neutrophils. There were no obvious changes in the colon, either macroscopically or histologically, and the feces were normal (solid stools). Leptospira was isolated from all the intestinal walls from the small intestine to the colon, the intestinal contents, and the feces. These findings suggest that the invasion of leptospires into the intestinal wall and the associated submucosal hemorrhage may be the cause of the gastrointestinal symptoms observed in leptospirosis. Furthermore, not only the urine of infected animals but also the feces could be a source of infection.

Gut microbiota involved in leptospiral infections

Leptospirosis is a re-emerging zoonotic disease worldwide. Intestinal bleeding is a common but neglected symptom in severe leptospirosis. The regulatory mechanism of the gut microbiota on leptospirosis is still unclear. In this study, we found that Leptospira interrogans infection changed the composition of the gut microbiota in mice. Weight loss and an increased leptospiral load in organs were observed in the gut microbiota-depleted mice compared with those in the control mice. Moreover, fecal microbiota transplantation (FMT) to the microbiota-depleted mice reversed these effects. The phagocytosis response and inflammatory response in bone marrow-derived macrophages and thioglycolate-induced peritoneal macrophages were diminished in the microbiota-depleted mice after infection. However, the phagocytosis response and inflammatory response in resident peritoneal macrophage were not affected in the microbiota-depleted mice after infection. The diminished macrophage disappearance reaction (bacterial entry into the peritoneum acutely induced macrophage adherence to form local clots and out of the fluid phase) led to an increased leptospiral load in the peritoneal cavity in the microbiota-depleted mice. In addition, the impaired capacity of macrophages to clear leptospires increased leptospiral dissemination in Leptospira-infected microbiota-depleted mice. Our study identified the microbiota as an endogenous defense against L. interrogans infection. Modulating the structure and function of the gut microbiota may provide new individualized preventative strategies for the control of leptospirosis and related spirochetal infections.

In Vivo Biofilm Formation of Pathogenic Leptospira spp. in the Vitreous Humor of Horses with Recurrent Uveitis

Equine recurrent uveitis (ERU) causes painful inflammatory attacks and oftentimes blindness in the affected eyes. The disease is considered a late sequela of systemic leptospirosis. The most effective therapy is the surgical removal of the vitreous (vitrectomy), which is not only therapeutic, but provides vitreous material that can be assessed diagnostically. For example, the lipL32 gene, culturable Leptospira spp., and anti-Leptospira antibodies have all been detected in vitreous samples obtained from eyes with chronic ERU. Despite this clear evidence of leptospiral involvement, the systemic administration of antibiotics in infected horses is ineffective at resolving ERU. This syndrome of chronic recurrent inflammation, which is unresponsive to antibiotic therapy, combined with apparent bacteria evading the immune response, is consistent with a biofilm-associated infection. The purpose of this study, therefore, was to detect the in vivo biofilm formation of Leptospira spp. in vitreous samples collected during vitrectomy and examined using a Warthin-Starry silver stain and immunohistochemistry. All known steps of biofilm formation were visualized in these samples, including individual Leptospira spp., leptospiral microcolonies and dense roundish accumulations of Leptospira spp. In many instances spirochetes were surrounded by an extracellular substance. Taken together, data from the present study show that ERU is a biofilm-associated intraocular leptospiral infection, which best explains the typical clinical course.