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Animal tuberculosis is a worldwide zoonotic disease caused principally by Mycobacterium bovis, a member of the Mycobacterium tuberculosis complex (MTC). In southern Iberian Peninsula, wild reservoirs such as the wild boar, among other factors, have prevented the eradication of bovine tuberculosis. However, most of the studies have been focused on south-central Spain, where the prevalence of tuberculosis is high among wild ungulates and cattle herds. In northern regions, where wild boar density and bovine tuberculosis prevalence are lower, fewer studies have been carried out and the role of this species is still under debate. The aim of this study was to describe the temporal and spatial distribution of antibodies against MTC in wild boar from the Basque Country, northern Spain. Sera from 1902 animals were collected between 2010 and 2016. The seroprevalence was determined with an in house enzyme-linked immunosorbent assay and the search of risk factors was assessed by Generalized Linear Models. Overall, 17% of wild boars (326/1902; 95%CI, [15.5%-18.9%]) showed antibodies against MTC. Risk factors associated with seropositivity were the year and location of sampling, the number of MTC positive cattle, the distance to positive farms and the percentage of shrub cover. Younger age classes were associated with increased antibody titres among seropositive individuals. The seroprevalence detected was higher than those previously reported in neighbouring regions. Hence, further studies are needed to better understand the role of wild boar in the epidemiology of tuberculosis in low tuberculosis prevalence areas and consequently, its relevance when developing control strategies.

The single and comparative intradermal tuberculin tests (SITT and CITT) are official in vivo tests for bovine tuberculosis (TB) diagnosis using bovine and avian purified protein derivatives (PPD-B and PPD-A). Infection with bacteria other than Mycobacterium tuberculosis complex (MTC) can result in nonspecific reactions to these tests. We evaluated the performance of the skin test with PPDs and new defined antigens in the guinea pig model. A standard dose (SD) of Rhodococcus equi , Nocardia sp., M . nonchromogenicum , M . monacense , M . intracellulare , M . avium subsp. paratuberculosis , M . avium subsp. avium , M . avium subsp. hominissuis , M . scrofulaceum , M. persicum , M . microti , M . caprae and M . bovis , and a higher dose (HD) of M . nonchromogenicum , M . monacense , M . intracellulare , M . avium subsp. paratuberculosis were tested using PPD-B, PPD-A, P22, ESAT-6-CFP-10-Rv3615c peptide cocktail long (PCL) and fusion protein (FP). The SD of R . equi , Nocardia sp., M . nonchromogenicum , M . monacense , M . intracellulare and M . avium subsp. paratuberculosis did not cause any reactions. The HD of M . nonchromogenicum , M . monacense , M . intracellulare , and M . avium subsp. paratuberculosis and the SD of M . avium subsp. hominissuis , M . scrofulaceum and M . persicum , caused nonspecific reactions (SIT). A CITT interpretation would have considered M . avium complex and M . scrofulaceum groups negative, but not all individuals from M . nonchromogenicum HD, M . monacense HD and M . persicum SD groups. Only animals exposed to M. bovis and M. caprae reacted to PCL and FP. These results support the advantage of complementing or replacing PPD-B to improve specificity without losing sensitivity.

European badgers ( Meles meles ) are reservoirs for animal tuberculosis (TB) in some European countries, complicating TB control in cattle. Badger vaccination and a deeper understanding of the subsequent protection mechanisms are necessary for effective TB control. In a previous study, two of eight badgers immunized with the heat-inactivated Mycobacterium bovis (HIMB) vaccine exhibited an unusual immune response (divergent), developing exacerbated lesions. The present study aimed to describe the local immune response in divergent badgers (those with severe disease progression), with respect to that observed in standard (where the vaccine showed efficacy) and control badgers. Immunohistochemistry was performed to evaluate immune cells (macrophages, T and B lymphocytes, plasma cells), and proteins (TGF-β, IL-10, Fox-P3) within TB granulomas in the lung and bronchial lymph node (LN), after TB challenge. Lung lesion volume, bacterial load and immunological response were also evaluated. The divergent immune response was characterized by elevated IL-10 and Fox-P3, few macrophages and high B lymphocytes (mainly in lungs), suggesting a Th1/Th2 imbalance with reduced Th1 cellular immunity leading to severe TB. In contrast, vaccinated badgers with a standard immune response showed a balanced response, with significantly lower bacterial loads (85.5% LN and 99.9% lung) than control group. This study provides new insights into the immune mechanisms in HIMB-vaccinated badgers, to improve TB control strategies.

The complexity of bovine tuberculosis (TB) epidemiology, especially in extensive livestock systems with wildlife reservoirs, calls for novel control strategies such as vaccination. This study evaluated the comparative efficacy of homologous and heterologous inactivated vaccines against that of the live Bacille Calmette–Guérin (BCG) vaccine on M. bovis isolation, gross TB lesions, and immune responses. Data from four controlled vaccination and challenge trials involving 41 calves were analysed. Animals were vaccinated with live BCG or heat-inactivated M. bovis via oral or parenteral routes, and immunologic and post-mortem analyses were conducted to evaluate vaccine performance. Compared with nonvaccinated controls, all vaccination strategies significantly reduced M. bovis bacterial loads in the lungs (up to 99%). However, bacterial loads in lymphoid tissues increased, confirming that tuberculosis is primarily a lymphatic disease. Diagnostic interference varied by vaccine type and administration route, with oral administration resulting in lower interference. Gross lesion scores were inconsistent across groups, suggesting limited utility as a measure of vaccine efficacy. Immune responses revealed increased detection of infection, particularly with inactivated vaccines. The lung bacterial load appeared to be decoupled from cellular immune responses, lymph node lesions and bacterial load, which were negatively correlated. Inactivated vaccines can offer a safe and effective means of reducing the bovine TB reproductive rate (R₀) even without total bacterial clearance. These findings highlight the need for revised evaluation criteria and support the integration of inactivated vaccines into TB control strategies.

Tuberculosis BCG vaccination induced non-specific protective effects in humans led to postulate the concept of trained immunity (TRAIM) as an innate type of immune mechanism that triggered by a pathogen, protects against others. Killed vaccines have been considered not to be effective. However, field efficacy of a commercial vaccine against paratuberculosis, as well as of a recently developed M. bovis heat-inactivated vaccine (HIMB) prompted to test whether it could also induce TRAIM. To this, we used a sarcoptic mange rabbit model. Twenty-four weaned rabbits were treated orally or subcutaneously with a suspension of either HIMB (10 7 UFC) or placebo. Eighty-four days later the animals were challenged with approximately 5000 S. scabiei mites on the left hind limb. Skin lesion extension was measured every 2 weeks until 92 days post-infection (dpi). Two animals were killed at 77 dpi because of extensive skin damage. The rest were euthanized and necropsied and the lesion area and the mite burden per squared cm were estimated. Specific humoral immune responses to S. scabiei and to M. bovis were investigated with the corresponding specific ELISA tests. Subcutaneously and orally HIMB vaccinated animals compared with placebo showed reduced lesion scores (up to 74% and 62%, respectively) and mite counts (−170% and 39%, respectively). This, together with a significant positive correlation (r = 0.6276, p  = 0.0031) between tuberculosis-specific antibodies and mite count at 92 dpi supported the hypothesis of non-specific effects of killed mycobacterial vaccination. Further research is needed to better understand this mechanism to maximize cross protection.

Tuberculosis (TB) in animals is a re-emerging disease with a wide range of hosts that causes large economic losses in livestock. Goats are particularly susceptible to TB and, in endemic areas, vaccination may be a valuable measure to control the disease. The main aim of this study was to evaluate the efficacy of parenteral vaccination of goats with a heat-inactivated Mycobacterium bovis (HIMB) vaccine, and compare it to M. bovis Bacille Calmette-Guérin (BCG) vaccine. Twenty-four goat kids were divided in 3 groups as following: HIMB vaccinated group (n = 8), BCG vaccinated group (n = 8) and unvaccinated group (n = 8). Afterwards, goats were experimentally challenged with Mycobacterium caprae by the endobronchial route. Antigen specific interferon-γ release assays and serology were performed after vaccination and challenge. Pathological and bacteriological parameters were evaluated after necropsy at 9 weeks post-challenge (p.c.). HIMB vaccine showed similar levels of protection to BCG in terms of volume reduction of thoracic TB lesions, presence of extra-pulmonary lesions, as well as a slight reduction of bacterial load in pulmonary lymph nodes. Moreover, HIMB vaccine did not induce interferences on the interferon-γ release assay based on reagents previously developed to differentiate infected from BCG vaccinated individuals. The results indicate that HIMB is a suitable vaccine candidate for further larger-scale trials under field conditions in goats.

Caprine tuberculosis (TB) causes a zoonotic disease with significant economic and health implications. However, excluding some regions, goat herds are not subjected to official TB eradication programs. Implementing vaccination protocols for this species could provide a complementary and effective control strategy against TB. We assessed the protective efficacy and immune response associated with a heat-inactivated Mycobacterium bovis ( M . bovis )-based immunostimulant (HIMB) applied intramuscularly against caprine pulmonary TB on 20 kid goats (10 immunized, 10 controls) naturally exposed to M . caprae infected goats for 10 months. TB-compatible lung lesions were assessed, alongside a local immune response analysis by immunohistochemistry of cell populations (Macrophages (MΦs), neutrophils, T, and B lymphocytes) and associated immune mediators (iNOS, TNF-α, IL-1α, IL-6, IFN-γ, TGF-β, IL-4). In the control group, 60% of the animals showed TB compatible lesions, compared with 40% of the immunized animals, which also showed a 78% reduction ( p  = 0.03) in the lesion severity score. Moreover, immunized animals showed a higher number of M1 MΦs ( p  = 0.03), producers of iNOS, as well as a higher expression of TNFα ( p  = 0.04) and IL-1α ( p  = 0.03). These mediators play a key role in the activation of a Th1-type cellular immune responses effective against mycobacteria, associated with a response of T lymphocytes expressing IFNγ, whose response was increased in the immunized group ( p  = 0.05). These results suggest that immunization with HIMB reduced the number and severity of TB-associated pulmonary lesions, which could be linked with an enhanced production of immune mediators with an essential role in the activation of MΦs with bactericidal functions.

Trained immunity is the capacity of innate immune cells to produce an improved response against a secondary infection after a previous unrelated infection. Salmonellosis represents a public health issue and affects the pig farming industry. In general, vaccination against salmonellosis is still facing problems regarding the control of distinct serovars. Therefore, we hypothesized that an immunostimulant based on heat inactivated Mycobacterium bovis (HIMB) could have an immune training effect in pigs challenged with Salmonella enterica serovar Choleraesuis ( S . Choleraesuis) and decided to explore the amplitude of this non-specific immune response. For this purpose, twenty-four 10 days-old female piglets were randomly separated in three groups: immunized group ( n  = 10) received orally two doses of HIMB prior to the intratracheal S . Choleraesuis-challenge, positive control group ( n  = 9) that was only challenged with S . Choleraesuis, and negative control group ( n  = 5) that was neither immunized nor infected. All individuals were necropsied 21 days post-challenge. HIMB improved weight gain and reduced respiratory symptoms and pulmonary lesions caused by S. Choleraesuis in pigs. Pigs immunized with HIMB showed higher cytokine production, especially of serum TNFα and lung CCL28, an important mediator of mucosal trained immunity. Moreover, immunized pigs showed lower levels of the biomarker of lipid oxidation malondialdehyde and higher activity of the antioxidant enzyme superoxide dismutase than untreated challenged pigs. However, the excretion and tissue colonization of S . Choleraesuis remained unaffected. This proof-of-concept study suggests beneficial clinical, pathological, and heterologous immunological effects against bacterial pathogens within the concept of trained immunity, opening avenues for further research.

This study aimed to assess the efficacy of a heat-inactivated Mycobacterium caprae (HIMC) vaccine in goats experimentally challenged with the same strain of M. caprae . Twenty-one goats were divided into three groups of seven: vaccinated with heat-inactivated Mycobacterium bovis (HIMB), with HIMC and unvaccinated. At 7 weeks post-vaccination all animals were endobronchially challenged with M. caprae . Blood samples were collected for immunological assays and clinical signs were recorded throughout the experiment. All goats were euthanized at 9 weeks post-challenge. Gross pathological examination, analysis of lung pathology using computed tomography, and bacterial load quantification in pulmonary lymph nodes (LN) by qPCR were carried out. Only HIMC vaccinated goats showed a significant reduction of lung lesions volume and mycobacterial DNA load in LN compared to unvaccinated controls. Both vaccinated groups showed also a significant reduction of the other pathological parameters, an improved clinical outcome and a higher proportion of IFN-γ-producing central memory T cells after vaccination. The results indicated that homologous vaccination of goats with HIMC induced enhanced protection against M. caprae challenge by reducing lung pathology and bacterial load compared to the heterologous vaccine (HIMB). Further large-scale trials are necessary to assess the efficacy of autovaccines under field conditions.

Animal tuberculosis (TB) is a complex animal health problem that causes disruption to trade and significant economic losses. TB involves a multi-host system where sheep, traditionally considered a rare host of this infection, have been recently included. The aims of this study were to develop an experimental TB infection model in sheep with a Mycobacterium caprae field strain isolated from a tuberculous diseased ewe, and to use this to evaluate the safety and efficacy of two vaccines against TB in sheep, the live-attenuated M. bovis BCG vaccine (Danish strain) and a heat-inactivated M. bovis (HIMB) vaccine. Eighteen 2 month-old lambs were experimentally challenged with M. caprae by the endotracheal route (1.5 × 103 CFU). They were separated per treatment group into parenterally vaccinated with a live BCG Danish strain vaccine (n = 6), orally vaccinated with a suspension of HIMB (n = 6) and unvaccinated controls (n = 6). Clinical, immunological, pathological and bacteriological parameters of infection were measured. All lambs were successfully infected and developed gross TB lesions in the respiratory system. The BCG vaccine conferred considerable protection against experimental TB in lambs, as measured by a reduction of the gross lesion volumes and bacterial load. However, HIMB vaccinated animals did not show protection. This study proposes a reliable new experimental model for a better understanding of tuberculosis in sheep. BCG vaccination offers an effective prospect for controlling the disease. Moreover alternative doses and/or routes of administration should be considered to evaluate the efficacy of the HIMB vaccine candidate.