AAVS_14_4_826-838

INTRODUCTION

Leptospirosis is a significant zoonotic disease of worldwide importance, caused by the bacteria of the genus Leptospira. Leptospirosis accounts for >1 million severe cases each year, with almost 59,000 deaths and ~2.9 million Disability-Adjusted Life Years (DALYs) lost. From an economic perspective, it has been estimated that this disease is responsible for annual production losses of approximately USD 52.2 billion worldwide, representing a significant burden on both the economy and global health (Muñoz-Zanzi et al., 2025). The primary reservoir for this bacterium is the rat; however, it can infect pets and humans. Leptospira is transmitted through its urine, where it can survive for months in the environment (Hernandez et al., 2025). This disease can certainly be transmitted to livestock such as cattle, pigs, and horses (Bonhomme and Werts, 2022).

Although leptospirosis is a disease with significant global implications, awareness remains low, especially in endemic areas. Many people are unaware that leptospirosis is caused by a microorganism, and most are unaware that contact with the urine of infected animals is a possible route of transmission. Understanding of the clinical signs of the disease, such as jaundice and kidney dysfunction, is also limited, and only a small proportion of the population is aware of simple preventive measures, such as the use of protective gear and avoidance of stagnant water. Furthermore, people are unaware that leptospirosis is a zoonotic disease, indicating a poor understanding of the mechanisms of interspecies transmission. This knowledge gap is exacerbated by social and cultural factors such as low levels of education and limited communication and health promotion, particularly in rural and resource-poor areas (Kitoki et al., 2025). Environmental factors also significantly contribute to increased risk of transmission. The proximity of settlements to stagnant water, frequent flooding, and the presence of open garbage piles encourage high populations of rats, which are the primary reservoir of Leptospira. Such environmental conditions provide an optimal habitat for bacterial survival, thus accelerating disease transmission in the population (Akbar et al., 2024).

In this infection, Leptospira spp. Colonize the kidneys, particularly the proximal tubules, and persist by evading the host’s immune response. The infection is generally subclinical; however, chronic colonization can lead to kidney damage (Maruoka et al., 2021). The bacteria are excreted in the urine starting 24-30 days after infection, and shedding may persist continuously depending on the strain and host factors (Monti et al., 2023). Colonization in the kidneys is also associated with histopathological lesions, particularly in the tubules and interstitium (Hailat et al., 2023). The clinical manifestations of leptospirosis are differentiated for both acute and chronic forms of the disease in cattle.

Acute conditions mainly affect offspring and young. In this case, the episodes are characterized by the occurrence of febrile, hemoglobinuria, and icteric cases, which in the worst case may result in death and foetal mortality. Some of the rare symptoms can include the gastrointestinal tract disorders, nasal bleeding, cough, swollen pasterns, blister-like lesions between the toes, and eyelid swelling. These are associated with disorders of the formed blood elements, particularly the variance in the volume of red blood cells of the single and multiple stages anemia. On the other hand, chronic leptospirosis mainly pertains to reproductive problems such as abortion, impaired fertility, stillbirth, weak calf syndrome, and prolonged calving. In addition, the subclinical form of infections, which are common in dairy cattle, are characterized by the drop in milk yield and some milder forms of fertility disorders. Systematic lesions are mainly manifested in the kidneys and the liver, which show placentitis of the chronically infected tissues, and the surrounding tissues are in a state of inflammation (Sohm et al., 2023).

Carvalho et al. (2024) also described how an epidemic of Leptospira abortion in Jersey dairy cows led to 40% of pregnant animals aborting and various episodes of stillbirths, with substantial economic losses for the farmers. The financial burden also extends to human cases, where treatment costs range from USD 128.94 to USD 845.77 per patient, with an average of USD 226.49. Uninsured patients incur slightly higher costs (USD 231.40) compared to those with insurance (USD 226.46), further illustrating the socioeconomic burden of this disease (Nugraheni et al., 2025).

Though the epidemiology and general pathogenesis of leptospirosis in livestock have been reviewed in detail, the literature (Chadsuthi et al., 2017; Shiokawa et al., 2019; Robi et al., 2024) tends to treat renal colonization, immune evasion, and reproductive outcomes as separate issues. However, there have been no review articles attempting to trace the molecular mechanisms of renal colonization in cattle and the pathways that lead to reproductive failure or reproductive loss in the form of abortion, fetal loss, subfertility, and infertility. This lack of treatise linking chronic renal infection, immune evasion, and reproductive pathology is an important unaddressed gap in knowledge. Hence, it is the objective of this review to integrate how livestock reproductive pathologies are an outcome of chronic renal colonization and persistent immune evasion, sustained by the interplay of pathogenesis, virulence factors, immune evasion mechanisms, and chronic infection. This is done in the context of how this knowledge impacts worldwide epidemiology and economic consequences, and, in this way, fills the gap in the literature.

Materials and Methods

This study was conducted using a narrative literature review approach to synthesize current knowledge regarding Leptospira spp. in bovine renal colonization and its association with reproductive disorders. Scientific articles were collected from reputable databases such as PubMed, Scopus, ScienceDirect, and Google Scholar. The literature search was performed using specific keywords, including “Leptospira in cattle,” “renal colonization,” “immune evasion,” “virulence factors,” and “reproductive disorders in bovine leptospirosis.” Articles published in the last 10–15 years were prioritized, while seminal older studies were also included when relevant.

RESULT AND DISCUSSION

General characteristics of Leptospira spp.

Leptospira is a helical-shaped bacterium belonging to the family Leptospiraceae, order Spirochaetales. It includes 21 species, which are classified into three groups based on their pathogenicity (pathogenic, intermediate, and saprophytic). More than 300 serovars of Leptospira have been described, based on the structure of lipopolysaccharides (LPS) located on their outer membrane (Eugene et al., 2014). Leptospira interrogans is a highly pathogenic organism. In the meantime, the second category may be pathogenic under certain circumstances, even though saprophytic strains generally do not cause disease (Sun et al., 2020).

These bacteria are aerobic, slow-growing, and extremely sensitive to desiccation and high salinity (Cameron, 2015; Samrot et al., 2021). Leptospira has a helical shape. These bacteria grow at least in part by lateral elongation, accomplished through the synthesis of peptidoglycan (Jutras et al., 2016). This morphology provides Leptospira with ready access to host tissues. Leptospira also has a protein called bactofilin, which maintains its helical structure and is involved in bacterial motility (Jackson et al., 2018). Leptospira possesses an outer membrane with multiple proteins critical to its survival (Nakamura, 2022).

The primary reservoir of Leptospira is rodents, and domestic animals can also become infected (Ricardo et al., 2018). In cattle, Hardjo serovar is composed of two serologically indistinguishable strains, but with different genotypic profiles: L. borgpetersenii serovar Hardjo (Hardjobovis), most often found in domestic ruminants, and L. interrogans serovar Hardjo (Harjoprajitno), endemic to multiple regions (Nally et al., 2018). Leptospira can survive in the environment for more than three weeks (Casanovas et al., 2018). This modification is presumably due to the endoproteins implicated in metabolism and energy production, which allow these bacteria to survive between hosts. In addition, molecular evidence supports the hypothesis that pathogenic strains originated from non-pathogenic ones by retaining most of the genes for exoproteins (Eshghi et al., 2015).

In cattle, the seroprevalence of leptospirosis increases with age. In the cattle population in the town of Bor in South Sudan, the seroprevalence rate reached 66.93% with MAT titers ≥100, whereas 21.65% (76/357) had a titers ≥800 indicating recent or ongoing infection. The subsequent Poisson regression analysis revealed that age is the only statistically significant risk factor, indicating that mature cattle were 1.43 times more likely to be seropositive than younger cattle (RR= 1.43; 95% CI = 1.09–1.92; P= 0.012). These results indicate that mature cattle have a greater risk of exposure to Leptospira over their lifespans and therefore a greater likelihood of being asymptomatic infection carriers. This population is typically asymptomatic, retaining the bacteria in their kidneys and excreting urine. Repeated exposure over a cow’s life not only increases seropositivity, but also the likelihood of asymptomatic infection which helps to sustain the environmental transmission cycle (Kasiano et al., 2025).

Leptospira spp. pathogenesis

Leptospira spp. Transmission can occur through two routes, namely direct contact and indirect contact (Figure 1). Direct contact occurs when humans or other animals come into direct contact with the urine of infected animals (Hamond et al., 2024). Meanwhile, indirect contact occurs through exposure to water, soil, or mud that is contaminated by the urine of infected animals, where Leptospira can survive for weeks to months (Nair and Gomes-Solecki, 2020). Infection occurs primarily through broken skin or mucous membranes because the outer layer of the skin, the stratum corneum, acts as the main barrier. These bacteria can easily pass through it if this layer is damaged or not functioning. After penetrating the skin or mucous membranes, Leptospira can migrate to the dermal tissue and quickly enter the bloodstream (Asoh et al., 2023).

Through the bloodstream, Leptospira spp. Spreads to vital organs, including the kidneys, liver, spleen, and lungs. In high-dose infections, the spread occurs more rapidly and can lead to severe disease, whereas in low-dose of infections, progression is slower. Variations in infection routes also play a role, as exposure to body cavities accelerates the spread compared to natural routes, although the target organs ultimately infected remain similar (Wunder et al., 2016).

Environmental factors and husbandry management also considerably influence whether a Leptospira infection develops as an acute disease, or remains as a chronic kidney- colonizing infection. Features such as the size and density of the livestock population, the husbandry system in use, the introduction of water surfaces, the cohabitation with canine and rodent species, and the husbandry of small ruminants (e.g. sheep, goats) may increase exposure to disease bacteria and amplify the severity of the disease. Co-infections with tissue-damaging pathogens, such as Brucella, Coxiella burnetii, or gastrointestinal nematodes may increase the fragmentation of the inflammation regulatory mechanisms with the amplified risk of reproductive tissue disorders and aggravation of the disease symptoms in the

affected domestic animal. All these factors influence the pathogenesis of leptospirosis in cattle, which, remarkably, lacks a defined pattern (Robi et al., 2024). Some research indicates that females exhibit a significantly higherinfection rate of 35.33%, while males only exhibit a 4% infection rate. This increased susceptibility in females could be attributed to different levels of exposure and more significant stress related to the gestational period, in addition to the more extreme higher reproductive losses (abortion, fetal loss, and repeat breeding) all of which are commonly related to infection by Leptospira (Ibrahim et al., 2022). L. interrogans is capable of invading various types of cells, including endothelium, renal tubule epithelium, and fibroblasts, through an endocytosis mechanism that depends on caveolae and integrin β1. The bacteria that enter are then enclosed in special vesicles (Lep-vesicles) that do not fuse with lysosomes, allowing the bacteria to survive inside the cell. Additionally, Leptospira can enter the layers of blood vessels and kidney cells through transcytosis, a mechanism of movement through cells that does not damage them, allowing the bacteria to spread freely throughout the body (Li et al., 2019).

In pregnant cows, the bacteremia phase also allows bacteria to cross the placenta and infect the fetus. One molecular investigation found that Leptospira spp. DNA was found in the following tissues: placenta (86.7%) and uterus (66.7%) of female cows. Additionally, the choroid plexus (50%), spleen (46.2%), and central nervous system (33.3%) of the embryos/fetuses were all PCR-positive (De Costa Barbane et al., 2024). All of these observations further support the reproductive system as a critical target in pathogenesis and suggest the existence of reproductive disorders and vertical transmission. In general, the processes of entry, spread, and invasion are more likely to be important for promoting chronic colonization in bovine renal tubules. This process is also modulated by defined virulence factors expressed by Leptospira spp., which will be further detailed in the following section.

Leptospira spp. virulence factors

Motility is a critical factor in Leptospira virulence. Pathogenic isolates are capable of a phenomenon known as crawling, which results in adherence to host kidney cells and sustained, directed motility of the bacteria. This mechanism would facilitate invasion into host cells. Periplasmic flagella mediate the movement of Leptospira and occur in two primary modes: swimming through liquid (e.g., blood) or crawling on body tissues (Xu et al., 2020). Additionally, Leptospira immunoglobulin-like proteins (LigA and LigB), surface adhesins, are involved in mediating bacterial attachment to extracellular matrix (ECM) molecules, including laminin, fibronectin, collagen types I and IV, hyaluronic acid, as well as chondroitin sulfate A and heparan sulfate (Hsieh et al., 2017).

It has been documented that some OMPs are virulence factors. One of these proteins, known as MPL36, is homologous to the rare lipoprotein (RlpA) and binds to plasminogen (PLG) through lysine residues located in the SPOR domain. PLG is then activated to form active plasmin, which can hydrolyze fibronectin, thereby enhancing the penetration and diffusion abilities of Leptospira (Zhu et al., 2023). In addition, the toluene tolerance protein (TolC) of the outer membrane of Leptospira, which interacts with various extracellular matrix (ECM) elements (laminin, fibronectin, collagen) and plasma proteins (fibrinogen, plasminogen), as well as immune factors like factor H, C3b, and C4BP, was also identified. These interactions enable the bacteria to adhere, survive, and escape the host immune system (Hota and Kumar, 2024). Additional proteins from the Leptospira membrane include LPS, Loa22, LipL71, LipL21, LipL32, LipL41, LigA, and LigB. The Leptospira is a double-membrane structure and therefore represents a crucial layer in host cell interactions (Hsu and Yang, 2022).

The formation of biofilm is also considered a virulence factor. Biofilms enable Leptospira to survive for an extended period in the environment and within the host, shielding them against environmental stress and host immune defense (dos Santos Ribeiro et al., 2025). Additionally, zinc is essential for maintaining the virulence of Leptospira interrogans. Transporter systems, including the ZnuABC system, TonB-dependent transporters, and ABC-type transporters, also play a role in regulating zinc homeostasis. A lack of zinc can alter the profile of proteins controlling pathogenicity, biofilm formation, and immune evasion (Hecktheuer et al., 2024).

Pathogenic Leptospira organisms express several toxins and enzymes that are crucial for disease pathogenesis, especially thermolysin protease and collagenase. Thermolysin belongs to the M4 family of metalloproteases and was found by bioinformatics methods as having a Peptidase_M4 domain. The enzyme was present in pathogenic species (L. interrogans, L. kirschneri, and L. noguchii) but not in intermediate or saprophytic species. The collagenase is based on a gene exclusively found in pathogenic strains ortholog LIC_12760 present in all pathogens except L. kmetyi. The two enzymes are involved in the tissue penetration and immune evasion by Leptospira (Fouts et al., 2016).

Of all the different virulence factors described, three appear to most affect the ability to attain and maintain chronic renal colonization. First, the ability to be motile, and more specifically to exhibit crawling motility, is critical for the bacteria to be able to get upstream against the flow of urine, breach renal epithelial surfaces, and persist within the proximal tubules. Second, the ability to produce certain adhesins such as LigA, LigB and select OMPs (including MPL36 and LipL32) is important for the firm attachment to extracellular matrix constituents of the renal tubules, thereby preventing their removal through any sort of mechanical washing. Third, the production of biofilms provides a favorable niche for the long-term existence of the leptospires in the renal milieu by preventing their susceptibility to immune-mediated destruction and to antimicrobial destruction. Collectively, these factors allow leptospires to not only access the renal tissues, but also to maintain a chronic renal colonization with very low morbidity and ultimately, to maintain a carrier state with continuous renal Leptospira shedding with important consequences on reproduction.

Kidney colonization in cattle

Kidney colonization is a hallmark of Leptospira spp. Infection in reservoir animals, including livestock and pets. The bacteria enter the host, travel to the kidneys, and become established in the renal tubules. The colonization of animal kidneys by Leptospira causes little to no damage that can be easily repaired, allowing chronic infection to persist in the long term. Once the bacteria have infected the kidneys, animals can shed Leptospira in urine for 542 days. The highest risk for transmission is when performing activities such as pen cleaning, passing through the environs of pens, and washing animals. If livestock are infected, the surrounding environment may be contaminated by urine containing Leptospira (Daud et al., 2018; Ginting and Indiarjo, 2022; Nuha et al., 2023).

Histopathological lesions caused by Leptospira colonization in bovine kidneys show a relatively consistent pattern across various countries (Table 1). Interstitial nephritis and glomerulonephritis are frequently reported findings in Indonesia, Malaysia, Jordan, Iran, Nigeria, and Brazil. Additionally, renal tubular damage, characterized by necrosis, epithelial degeneration, and hyaline cast formation, has also been observed (Saglam et al., 2022; Ajayi et al., 2020; Kamaruzaman et al., 2023). These findings indicate that the kidneys are the primary site of Leptospira colonization and the center of pathological changes.

Interstitial nephritis occurs in Leptospira infections because the bacteria directly invade the kidney tissue. Leptospira penetrates the kidney tissue, particularly the interstitium, resulting in mononuclear cell infiltration and inflammation. LipL32 plays a role in activating TLR2, which induces an inflammatory signal cascade. This activation promotes IL-1β, TNF-α, and MCP-1, which carry immune cells to the renal interstitium, causing interstitial nephritis (Wu and Wu, 2019). Meanwhile, glomerulonephritis (GN) is

Table 1: Histological lesions of kidney colonization by Leptospira spp. in cattle globally.

Author (Year)	Country	Sample	Histopathological findings
Hailat et al. (2023)	Jordan	152 Kidneys	Interstitial nephritis; Glomerulonephritis; Acute tubular necrosis; Congestion; Hyaline material deposition
Kamaruzaman et al. (2023)	Malaysia	50 Kidneys	Glomerular atrophy; Cytoplasmic hyaline droplets; Hyaline casts in glomeruli; Interstitial inflammatory infiltration (neutrophils, lymphocytes); Renal tubular necrosis; Vascular margination of inflammatory cells; Eosinophilic hyaline droplets in tubular epithelial cells
Rahayu et al. (2021).	Indonesia	28 Kidneys	Interstitial nephritis; Hemorrhage; Fibrosis
Suprayoga et al. (2020)	Indonesia	15 kidneys	Interstitial nephritis; Glomerulonephritis; Perivasculitis; Atherosclerosis; Nephrosis; Fibrosis
Magalhaes et al. (2020)	Brazil	100 kidneys	Tubular hyalinization; Congestion; Interstitial nephritis; Glomerulonephritis; Calcification; Cellular necrosis; Steatosis; Hemosiderosis; Amyloidosis; Glomerular edema
Saglam et al. (2020)	Turkey	70 Kidneys	Diffuse focal interstitial nephritis; Hemorrhages; Tubular epithelial degeneration; Tubular desquamation; Tubular necrosis; Hyaline casts in tubular lumen; Inflammatory infiltration of glomeruli and tubules; Glomerular atrophy
Ajayi et al. (2020)	Nigeria	108 Kidneys	Interstitial nephritis; Tubular nephrosis; Lymphoplasmacytic infiltration; Tubular necrosis; Glomerular and tubular atrophy; Renal hemorrhage; Interstitial fibrosis
Taghadosi et al. (2016)	Iran	205 Kidneys	Chronic nephritis; White spots; Petechial hemorrhages; Adhesions; Kidney stones; Hydatid cysts; Congestion; Hydronephrosis

Table 2: Reproductive disorders in cattle due to Leptospira spp. infection globally.

Author (Year)	Country	Sample population	Diagnostic method	Reproductive impact
Robi et al. (2024)	Ethiopia	461 Cattle	ELISA	L.Hardjo seropositivity increases the risk of abortion; dystocia; retained fetal membranes; repeat breeding
Macchi et al. (2024)	Uruguay	31 beef cattle	MAT; qPCR	Seropositivity and urinary shedding associated with infertility
Pedrosa et al. (2023)	Brazil	54 non-pregnant subfertility cows	PCR; IL-6 ELISA	Uterine inflammation linked to embryo death and subfertility
dos Santos Pereira et al. (2022)	Brazil	251 asymptomatic diary cows	PCR (follicular fluid)	67 (26.7%) positive for Leptospira DNA; Silent ovarian infection
Ikpe et al. (2021)	India	130 crossbred cows	MAT	Abortion; repeat breeding; endometritis; postpartum anestrus; retained fetal membranes.
Aymée et al. (2021)	Brazil	9 cows with reproductive failure	MAT; PCR; sequencing	Infertility; abortion; estrus repetition; Leptospiral DNA in the cervico-vaginal mucus and uterus.
Oliveira et al. (2021)	Brazil	216 cows (9 herds)	MAT; ultrasonography	Embryonic death; abortion; Sejroe linked to embryonic loss, Icterohaemorrhagiae linked to abortion
Di Azevedo et al. (2020)	Brazil	42 non-pregnant cows	MAT; PCR	Leptospira DNA detected in uterus (9 cows)

caused by increased vascular permeability of the glomerular capsule. The primary mechanism is the interaction of Leptospira with VE-cadherin on endothelial cells, which regulates intercellular junctions and increases permeability. This mechanism causes extravasation of red blood cells and fibrin into the urinary space, resulting in exudative GN. Changes in the cell membrane lead to increased vascular permeability, resulting in increased vascular leakage. Vascular damage and the effects caused by Leptospira lead to glomerular damage, characterized by areas of necrosis and fibrinoid changes. GN in leptospirosis occurs due to endothelial damage (Hilbe et al., 2024). High TGF-β expression can lead to renal fibrosis, while in asymptomatic carrier animals, downregulation of TGF-β may help prevent tissue damage (Cagliero et al., 2018).

Leptospira colonization of the kidneys is often characterized as having a few subclinical features which heal with little to no intervention over a period of time, however, the more chronic and persistent infections affected kidneys may experience more serious lesions such as tubular necrosis and fibrosis with accompanying nephritis to name a few. The second infection is more serious as this time the host is colonized and able to shed virulent organisms. The repair responses to this infection are limited and do to mild damage which allows the evading immune response to remain inactive. LipL32, the virulence protein for Leptospira, interacts with TLR2, a receptor for immune cells, to further dampen the response of immune cells by allowing them to stay dormant within a tissue. TGF-β/Smad, a pathway activated by the immune system which is chronic and self stimulating, leads to further mild fibrosis interstitial to the tissue. This interstitial fibrosis is often the only type of fibrosis seen in exposed tolerant hosts and it allows for the kidneys to remain functioning. The immune response with tissue damage are balanced in a way to allow Leptospira to stay active and colonized within the host, demonstrating the complex interwoven response of colonization within the kidneys (Chou et al., 2023).

Reproductive effects

The reproductive tract infections caused by leptospirosis in cattle were initiated by Serogroup Leptospira spp. in particular the serovars Hardjoprajitno and Hardjobovis. These two serovars have been noted to have high infective potential and are capable of adjusting to the compartmentalized reproductive tissues of the reproductive tract and, in particular, the uterus, leading to chronic endometritis and subsequent reproductive pathologies of the host such as reproduction failures (miscarriage, abortion and subfertility). In addition to the systemic manifestations resulting from the kidneys, recent studies suggest Leptospira can infiltrate the uterus. Molecular-based diagnostic approaches have confirmed the Leptospira organism in the uterine tissues of cattle and were reproductively compromised, despite negative urine samples, suggesting that the colonization of the uterus can occur without renal colonization (Aymée et al. 2024). Infected uterine tissues are characterized by the production of inflammatory cytokine IL-6, resulting in an inflammatory response that alters the uterine milieu essential for the implantation of a conceptus and embryo support and development. This inflammation impacts the uterine epithelium and alters the mid-cycle-endometrial asynchrony, further creating an adverse milieu for embryo formation and longevity. Therefore, the incidence of subfertility, failures of embryo implantation, and embryo demises are raised considerably (Pedrosa et al., 2023).

Leptospira spp. infection causes several reproductive abnormalities in cattle in various countries (Table 2). The most common reproductive effects are abortion, infertility, embryonic death, and repeat breeding. Robi et al. (2024) reported that in Ethiopia, seropositivity to the Hardjo serotype was found to increase the potential for abortion, dystocia, fetal membrane retention, and repeat breeding. These results are supported by a study in India where Leptospira-positive cattle experienced abortion, endometritis, and postpartum anestrus (Ikpe et al., 2021). This certainly provides evidence of the serious direct effects of leptospirosis on the reproduction of female cattle.

There are also variations in reproductive effects between countries and diagnostic methods. In Uruguay, seropositivity was found to be associated with urinary shedding, as detected by qPCR, in cases of infertility in beef cattle (Macchi et al., 2024). Molecular approaches in Brazil have provided evidence of Leptospira DNA in follicular fluid (dos Santos Pereira et al., 2022), vaginal mucus (Cerico), and the uterus (Aymée et al., 2021). Furthermore, Oliveira et al. (2021) reported that reproductive outcomes can be influenced by serogroup variation, where in this study the Sejroe serogroup was associated with embryo death, while the Icterohaemorrhagiae serogroup was found in abortion cases. Additionally, Pedrosa et al. (2023) reported a relationship between uterine inflammation, characterized by increased IL-6, and embryo death and subfertility. This clearly demonstrates that Leptospira colonization is not limited to the kidneys but can affect reproductive organs, even in animals without clinical signs of follicular disease (dos Santos Pereira et al., 2022).

Leptospira spp. immune evasion strategies

Leptospira spp. are able to modulate the innate immune response in cattle, including in the preputial mucosa. Initial activation of the immune system is characterized by increased TLR2 expression and cytokine production that triggers IFN-β and IFN-λ as an early defense response (Pla et al., 2025). However, this activation does not result in complete elimination because Leptospira possess various immune evasion mechanisms. The bacteria can survive within cells by forming Lep-vesicles that fail to fuse with lysosomes, thus avoiding degradation (Li et al., 2019). Furthermore, Leptospira are able to evade or damage Neutrophil Extracellular Traps (NETs), which normally trap and kill pathogens (Scharrig et al., 2015).

The complement system can also be inactivated through binding to host regulators such as factor H (FH), FH-like protein, C4b-binding protein (C4BP), and vitronectin (Vn), which collectively inhibit MAC formation and accelerate the deactivation of C3b and C4b (Fraga et al., 2016). Surface lipoproteins such as ErpY-like and LcpA also play a role in this evasion through the acquisition of FH and FI, thus protecting the bacteria from lysis (Hota et al., 2022; Shankar et al., 2024).

At the adaptive immune level, Leptospira modulate immune cell activity through outer membrane proteins such as Loa22 and Len, which bind to the extracellular matrix and interfere with T cell activation and antigen presentation (Kumar et al., 2022). The A11 fragment of LigA can activate signaling pathways that trigger cytokine production and immune cell activation. However, Leptospira can suppress LigA expression or undergo antigenic variation to maintain chronic infection (Kumar et al., 2021). Furthermore, LipL21 inhibits myeloperoxidase (MPO) activity in neutrophils, reducing the formation of microbicidal radicals such as HOCl and decreasing neutrophil killing ability (Vieira et al., 2018).

Chronic kidney colonization reflects a balanced form of immune modulation. Although increased numbers of CD4 T cells and B cells specific to Leptospira antigens are found in renal lymph nodes, this response does not result in significant inflammation or tissue damage, suggesting the establishment of a state of local immune tolerance (Nally et al., 2018). Imbalanced cytokine production during the course of infection can increase IL-1β, TNF-α, and IL-6, while the body responds by increasing the production of anti-inflammatory cytokines such as TGF-β. Under certain conditions, increased TGF-β can reduce excessive inflammatory responses and contribute to the achievement of an immune modulation state that supports long-term bacterial persistence (Cagliero et al., 2018).

In infected uterine tissue, increased IL-6 reflects local inflammation caused by Leptospira infection. This alters the uterine environment necessary for embryo implantation and development (Pedrosa et al., 2023). Inflammation also affects follicle development, indirectly influencing the oocyte’s ability to survive infection (dos santos Pereira et al., 2022). This modulated immune response reflects the progression of infection, shifting from initial inflammatory activation to local tolerance that maintains long-term colonization, both in the kidney and the reproductive tract.

Global epidemiological and economic implications

Leptospirosis is a widespread zoonotic disease worldwide caused by pathogenic Leptospira, which has a heterogeneous spectrum of clinical presentation, including mild disease and debilitating pulmonary-hepatorenal illnesses. The disease is transmitted by exposure to contaminated urine, and direct or close contact with the secretions of infected animals, including rodents, livestock, and pets (Khan et al., 2018). Environmental and behavioral risk factors such as warm climates, flooding, poor sanitation, and occupation exposure greatly affect the disease’s distribution in tropical and subtropical areas (Karpagam and Ganesh, 2020; Torgerson et al., 2015; Costa et al., 2015), but they are not sufficient to explain the the disease’s persistence. The biological attributes of the Leptospira, including motility, adhesion, biofilm formation, kidney colonization, evasion of the host’s immune system, and other mechanisms of long-term chronic infection, drive an even greater global prevalence of the disease.

Environmental persistence of the organisms depends on Leptospira-contaminated areas and on the prolonged survival in humid and flooding areas. The presence of rodent reservoirs in those areas, fortifies the survival of the pathogen. However, the ability of Leptospira to withstand vegetative and other hostile environmental factors is also strengthened by its biofilm forming capacity which allows survival in stagnant water, soil, and in poorly kept traditional markets (Yuangga et al., 2022). Therefore, disruption of the virulence mechanisms in the bacteria along with environmental control measures should be adopted to successfully achieve control on a global scale.

New opportunities exist due to mechanistic progress which go far beyond classical rodent control. Pathogenesis and the motility, adhesins, and surface proteins are pivotal to Leptospirosis. These are specific molecular targets for minimizing renal colonization and diminishment of transmission. For instance, virulence components LigA, LigB, and other serum outer membrane proteins are critical for immune evasion and for being resistant to serum (Aymée et al., 2024; Fernandes et al., 2021). Inhibition of these adhesins is likely to reduce bacterial attachment, hinder early invasion of tissues, and reduce the lasting occupation of kidneys. Just as the knowledge that the CsrA overexpression (Phoka et al., 2021) greatly impedes motility in L. interrogans provides the promise of therapeutically targeting motility to frustrate the crawling of L. interrogans and consequently, its ability to ascend the renal tubules and colonize.

The development of genetic technology in functional studies also is influenced by the development of CRISPR interference (CRISPRi) for the first time of gene silencing without alteration of genomic DNA. Key proteins resistant to serum and for immune evasion are being identified (Fernandes et al., 2021). Such knowledge is valuable for the design of next-generation vaccines and/or targeted inhibitors to virulence factors that need to be present for persistence.

Research shows that while some vaccines can prevent disease, other diseases, such as kidney colonization, remains. Research shows that antibodies can block colonization, yet there is still some lack of protection as well (Evangelista et al., 2017). Research shows that there needs to be other approaches to vaccine methodologies. Utilizing other approaches to vaccines, such as Multivalet vaccines, focusing on other mechanisms of immune evasion (Techawiwattanaboon et al., 2019). Some research shows that vaccines can show reduce efficacy (de Oliveira et al., 2023).

Research shows that there chronic colonization which leads to your persistent IgM responses (Vernel-Pauillac et al., 2021). Due to colonization of kidneys it leads to shedding and can contaminate the surrounding environment, which has not been solved yet. Contaminated colonization can be solved by targeting little but multiple at a time. Combining approaches can also be used to get more of a total reduction of the impact of the disease.

CONCLUSIONS

There are several virulence mechanisms which Leptospira uses to colonize the bovine kidney, and cause persistent infection and recurrent urinary shedding, without the animal being aware, so the animal can retain the infection and suffer long-time reproductive failure. This review attempts to describe the relationship of renal pathogenesis, immune modulation, reproduction, and chronic infection to the unique and considerable animal and worldwide economic impacts of the disease. Mechanism-based disease control appears possible, and should focus on the biofilm exopolysaccharide, and other factors that control motility and invasion of renal tissues and that control colonization. Selected biofilm and renal colonization factors should be the focus of next generation vaccines and therapeutics. Strengthening one health initiatives and the surveillance and sanitation of animal and fecal wastes should be the main and coordinated focus.

Acknowledgements

The work was supported by Universitas Airlangga under the Research Grant for Academic Publication Program.

Novelty Statement

This review presents a novel integrative perspective by linking renal colonization, immune evasion mechanisms, and reproductive disorders caused by Leptospira spp. in cattle into a unified pathogenic continuum. Unlike previous studies that addressed these aspects in isolation, this work highlights chronic kidney infection as the central driver of persistent bacterial shedding and reproductive failure. Furthermore, it emphasizes the molecular interplay of virulence factors such as motility, adhesion, and biofilm formation in sustaining long-term colonization and immune modulation. This comprehensive approach provides new insights into the pathogenesis of bovine leptospirosis and identifies potential mechanism-based targets for developing next-generation vaccines and therapeutic strategies.

Author’s Contribution

RW was responsible for the conceptualization, comprehensive literature review, manuscript drafting, and final revision. YP supervised the study, validated the data, and contributed to the review and editing process. HMR conducted the critical review, formatting, and approval of the final version. MIRF contributed to data validation, reference verification, and refinement of the manuscript’s methodological framework. CNZ assisted in literature synthesis, visualization, and language editing. All authors have read and approved the final version of the manuscript.

Generative AI and AI-assisted technology statement

The authors declare that no generative AI or AI-assisted technologies were used in the writing, data analysis, or preparation of this manuscript.

Conflicts of interest

The authors have declared no conflict of interest.

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