Genetic Analysis of LigA, LipL32, Loa22, and OmpL1 Antigens from Leptospira spp. Sejroe Serogroup: How Close We Are To a Vaccine Against Bovine Leptospirosis?

Bovine leptospirosis has as main causative agents Leptospira spp. from Sejroe serogroup. Vaccination is a crucial step to control this infection. The use of conserved proteins among Leptospira spp. is of great importance for a protective immune response. The aim of the present study is to genetically analyze antigens of Leptospira spp. from Sejroe serogroup strains isolated from cattle for a preliminary evaluation of vaccine candidates. Genes associated with antigenicity-LigA, LipL32, Loa22, and OmpL1-were analyzed through bioinformatic and immunoinformatic tools. Despite high diversity observed in strains, on an amino acid level, highly conserved regions were observed (> 90%), particularly in LipL32 gene. Moreover, highly conserved amino acid regions (> 30 aa) were observed in all genes, regardless of species, geographical origin or biological source of isolation. Superposed structures of protein fragments including all the predicted MHC-II and B-Cell epitopes were demonstrated. Results presented herein are preliminary, but a fundamental step towards the development of an efficient vaccine against bovine leptospirosis, a silent but enormously concerning disease.

Review: Bovine foetal mortality - risk factors, causes, immune responses and immuno-prophylaxis

This review of bovine foetal mortality (>42 d gestation) concluded that while the majority of risk factors associated with sporadic loss operate at animal-level, e.g. foetal plurality, those that operate at herd-level, e.g. some foetopathogenic infections, are more likely to result in abortion outbreaks. While the causes of foetal mortality have traditionally been classified as infectious and non-infectious, in fact, the latter category is a diagnosis of exclusion, generally without determination of the non-infectious cause. This review has also established that the traditional dichotomisation of infectious agents into primary and secondary pathogens is based on a flawed premise and these terms should be discontinued. The delicate balance of the maternal gestational immune system between not rejecting the allograft (conceptus) but rejecting (attacking) foetopathogens is stage-of-pregnancy-dependent thus the timing of infection determines the clinical outcome which may result in persistent infection or foetal mortality. Utilisation of our knowledge of the materno-foetal immune responses to foetopathogenic infection has resulted in the development of numerous mono- and polyvalent vaccines for metaphylactic or prophylactic control of bovine foetal mortality. While some of these have been shown to significantly contribute to reducing the risk of both infection and foetal mortality, others have insufficient, or conflicting evidence, on efficacy. However, recent developments in vaccinology, in particular the development of subunit vaccines and those that stimulate local genital tract immunity, show greater promise.

The Efficacy of Vaccination in the Prevention of Renal and Genital Leptospirosis in Experimentally Infected Sheep

(1) Background: Leptospirosis, mainly determined by strains belonging to serogroup Sejroe, has a direct impact on the reproductive efficiency of ruminants, such as sheep. In Brazil, Leptospira santarosai serovar Guaricura, known to be able to chronically colonize the uterine environment, is of special note. Although vaccination minimizes the effects of acute disease, whether or not it can protect from renal colonization remains controversial, and its effects on the genital tract are unknown. In this context, the present study aims to investigate the efficacy of vaccination in the prevention of experimental genital leptospirosis. (2) Methods: Eighteen sheep were divided into three groups: one vaccinated with a polyvalent commercial bacterin, one vaccinated with an autologous bacterin, and one unvaccinated. After 14 days, the sheep were experimentally challenged with 10⁸ leptospires (L. santarosai, serogroup Sejroe, serovar Guaricura, strain FV52) intraperitoneally. Serology and colonization of the urinary and genital tracts were carried out monthly by PCR for 210 days in all animals. (3) Results: Vaccination significantly elicited antibody titers with a predominance of agglutinins against serogroup Sejroe. Both urinary and genital infections were confirmed by PCR. Positivity in urine PCR was absent after D120, while genital infection persisted until the end of the study. Serological results and the finding that vaccination did not avoid renal colonization align with previous studies. Despite vaccination, Leptospira established chronic and asymptomatic colonization of the genital tract until D210, an outstanding finding that remains to be fully understood in its mechanisms. (4) Conclusions: This is the first study conducted to analyze the effects of vaccination in the prevention of genital leptospirosis.

Pathogenic Leptospira spp. Seroprevalence and Herd-Level Risk Factors Associated with Chilean Dairy Cattle

Leptospirosis is a ubiquitous distributed zoonotic infectious disease present in wild and domestic animals. This study aimed to estimate within-herd and herd-level seroprevalence against pathogenic Leptospira spp. in dairy cows from southern Chile and identify risk factors associated with the herd-level status. We used a multi-stage strategy combined with a stratified sample strategy for randomly sampling 147 herds and 4876 lactating cows. We considered as infected a herd with at least one positive reactor to MAT. In addition, an epidemiological survey was applied to the herd's owners and a logistic regression (LR) model was constructed to analyze it. The overall within-herd prevalence was 5.9% (95% CI 4.9-6.8), the overall herd-level prevalence was 42.2% (95% CI 9.2-47.9), and there was variation in both between different herd sizes. L. borgpetersenii serovars Hardjo and Tarassovi and L. interrogans serovar Pomona were the more frequent serovars in non-vaccinated herds. A factor that decreases the risk of a farm being infected was Leptospira vaccine usage (OR = 0.04; 95% CI = 0.02-0.11), and variables that increase risk were using bulls for mating (OR = 3.43; 95% CI = 1.1-10.1) and continuous calving distribution (OR = 3.4; 95% CI = 1.3-8.8). The study's results will contribute to unravelling the infection burden in the main dairy area of the country and designing control strategies.

AN AGE STRUCTURE MODEL WITH IMPULSE ACTIONS FOR LEPTOSPIROSIS IN LIVESTOCK CATTLE

As a zoonotic disease, leptospirosis has now been identified as one of the emerging infectious diseases. In this paper, we analyze the propagation of leptospirosis and find a schedule for control programs to eradicate the disease in a cattle ranch. A mathematical model has been built with ordinary differential equations (ODEs) to understand the epidemiology of leptospirosis and main factors on its transmission. We investigated the disease free equilibrium of the model and its stability using the basic reproduction number, [Formula: see text], and target reproduction number, [Formula: see text]. Then, the model incorporates vaccination and recruitment control programs in the form of impulse actions as measures to prevent the propagation of leptospirosis in the ranch. Parameter estimation and sensitivity analysis are presented as a part of this study.

Genital bovine leptospirosis: A new look for an old disease

Bovine leptospirosis is often associated with host-adapted leptospires infections, such as strains belonging to the Sejroe serogroup. Although bovine leptospirosis by adapted strains may result in abortions, fetal death, premature births and the birth of weak and/or low-weight calves, this infection is more closely associated with subtler syndromes, such as subfertility and early embryonic death. In this way, this silent disease can go unnoticed and undiagnosed, compromising reproductive efficiency with a consequent decrease in the productivity of herds over long periods. For many years, genital tract infection has been considered a secondary effect of renal infection with the assumption being that leptospires are found in the genital tract due to bacteremia caused by renal colonization. In contrast to this hypothesis, there is some evidence in the literature that suggests that genital leptospirosis should be considered a specific syndrome dissociated from renal/systemic disease. Therefore, this paper aims to gather and critically analyze information about genital leptospirosis in cattle, considering the disease a distinct syndrome, herein denominated bovine genital leptospirosis (BGL), that requires a unique approach to diagnosis and treatment.

Dynamics of humoral response in naturally-infected cattle after vaccination against leptospirosis

Vaccination is one of the most important measures for the control of bovine leptospirosis. Despite the broad usage of vaccination against leptospirosis in cattle worldwide, the dynamics of the post-vaccine immune response remain controversial and many aspects are still unclear, particularly in naturally-infected animals. Thus, the objective of this study is to describe the dynamics of humoral response in naturally-infected cattle after vaccination against leptospirosis. A total of 162 cows were studied, consisting of 129 included in the experimental group (G1), and subdivided into two groups, vaccinated with two different brands of bacterins, as well as 33 in the control group (G2). Serology (MAT) was performed in all cows on D0 (vaccination), then 60 and 120 days post-vaccination. Vaccination significantly elicited the production of anti-leptospiral antibodies. Seroreactivity increased rapidly but was of short duration (up to D60). Significantly, that increase was notably higher in the vaccinated group than in the controlled. Both vaccines elicited a similar response with a higher rate of seroreactive animals, but predominately against different serogroups. In this context, our results reinforce that, although of limited duration, vaccination against leptospirosis significantly elicits a specific humoral response in naturally-infected animals. The two studied vaccines presented similar seroconversion levels, but predominantly to different serogroups, being one against Icterohaemorrhagiae and the other against Sejroe.

Control of bovine leptospirosis: Aspects for consideration in a tropical environment

Due to the complex and dynamic epidemiology of leptospirosis on livestock, control is still controversial and frustrating. In this context, this paper discusses the main challenges and perspectives for the control of bovine leptospirosis, particularly under tropical conditions. In order to reduce the effects of the disease in cattle, it has been proposed that the control should integrate the trinomial antibiotic therapy (mainly streptomycin); vaccination (whole-cell bacterins); and environmental management. This last element should be carefully considered in tropics. Despite the enormous economic impact of the disease, mainly on its chronic and silent reproductive presentation, research on control programs is not proportional. Conversely, the number of studies regarding the new vaccine strategies, such as recombinant antigens has been increasing and should be encouraged.

High frequency of leptospiral vaginal carriers among slaughtered cows

Bovine leptospirosis is one of the most important reproductive diseases that compromise the productivity of cattle farming. However, the presence of the agent on vaginal environment is still poorly understood in cattle. Considering this context, the present study aimed to detect the presence of pathogenic Leptospira sp. in vaginal fluid (VF) of cows. VF and urine were collected from 254 cows from a slaughterhouse for bacteriological culture and PCR (lipL32 gene). Overall, eleven pure culture (4.3%) of leptospiral isolates were obtained. Leptospiral DNA was detected in 128 (50.4%) of VF samples and 81 (31.0%) of urine samples, while on 75 (29.5%) it was exclusively in VF and 28 (11.3%) only in the urine. Detection of leptospiral DNA and the recovery of viable leptospires from VF of a high number of cows without apparent symptoms highlight the role of vaginal carriers and indicate that venereal transmission (female-to-male) could occur in that species. Moreover, VF should be encouraged as a valuable sample for diagnosis of bovine genital leptospirosis.

Assessing the impact of tailored biosecurity advice on farmer behaviour and pathogen presence in beef herds in England and Wales

The term 'biosecurity' encompasses many measures farmers can take to reduce the risk of pathogen incursion or spread. As the best strategy will vary between settings, veterinarians play an important role in assessing risk and providing advice, but effectiveness requires farmer acceptance and implementation. The aim of this study was to assess the effectiveness of specifically-tailored biosecurity advice packages in reducing endemic pathogen presence on UK beef suckler farms. One hundred and sixteen farms recruited by 10 veterinary practices were followed for three years. Farms were randomly allocated to intervention (receiving specifically-tailored advice, with veterinarians and farmers collaborating to develop an improved biosecurity strategy) or control (receiving general advice) groups. A spreadsheet-based tool was used annually to attribute a score to each farm reflecting risk of entry or spread of bovine viral diarrhoea virus (BVDV), bovine herpesvirus-1 (BHV1), Mycobacterium avium subsp. paratuberculosis (MAP), Leptospira interrogans serovar hardjo (L. hardjo) and Mycobacterium bovis (M. bovis). Objectives of these analyses were to identify evidence of reduction in risk behaviours during the study, as well as evidence of reductions in pathogen presence, as indications of effectiveness. Risk behaviours and pathogen prevalences were examined across study years, and on intervention compared with control farms, using descriptive statistics and multilevel regression. There were significant reductions in risk scores for all five pathogens, regardless of intervention status, in every study year compared with the outset. Animals on intervention farms were significantly less likely than those on control farms to be seropositive for BVDV in years 2 and 3 and for L. hardjo in year 3 of the study. Variations by study year in animal-level odds of seropositivity to BHV1 or MAP were not associated with farm intervention status. All farms had significantly reduced odds of BHV1 seropositivity in year 2 than at the outset. Variations in farm-level MAP seropositivity were not associated with intervention status. There were increased odds of M. bovis on intervention farms compared with control farms at the end of the study. Results suggest a structured annual risk assessment process, conducted as a collaboration between veterinarian and farmer, is valuable in encouraging improved biosecurity practices. There were some indications, but not conclusive evidence, that tailored biosecurity advice packages have potential to reduce pathogen presence. These findings will inform development of a collaborative approach to biosecurity between veterinarians and farmers, including adoption of cost-effective strategies effective across pathogens.