Protection of Eurasian badgers (Meles meles) from tuberculosis after intra-muscular vaccination with different doses of BCG

Wildlife Immune Responses to Mycobacterium bovis and to Bacille of Calmette-Guerin

Bovine tuberculosis (bTB) is a zoonotic bacterial disease presenting public health, veterinary, and economic threats around the globe. Although cattle producers rely on regular testing and management practices to minimize domestic herd exposure, wildlife species around the world continue to be the main reservoirs for disease. Wildlife reservoirs for bTB include the Eurasian badger (Meles meles) in Great Britain and Ireland, the brushtail possum (Trichosurus vulpecula) in New Zealand, wild boar (Sus scrofa) in Spain, as well as white-tailed deer (Odocoileus virginianus) in the United States and red deer (Cervus elaphus) in Spain. Although all reservoir species share the ability to infect cattle, they differ in transmission capability, disease pathogenesis, diagnostic detection, and vaccination strategies. In this review, bTB interactions with these wildlife reservoirs are discussed, illustrating the need to address bTB disease in wildlife hosts to achieve eradication in domestic livestock.

Comparative pathology of experimental pulmonary tuberculosis in animal models

Research in human tuberculosis (TB) is limited by the availability of human tissues from patients, which is often altered by therapy and treatment. Thus, the use of animal models is a key tool in increasing our understanding of the pathogenesis, disease progression and preclinical evaluation of new therapies and vaccines. The granuloma is the hallmark lesion of pulmonary tuberculosis, regardless of the species or animal model used. Although animal models may not fully replicate all the histopathological characteristics observed in natural, human TB disease, each one brings its own attributes which enable researchers to answer specific questions regarding TB immunopathogenesis. This review delves into the pulmonary pathology induced by Mycobacterium tuberculosis complex (MTBC) bacteria in different animal models (non-human primates, rodents, guinea pigs, rabbits, cattle, goats, and others) and compares how they relate to the pulmonary disease described in humans. Although the described models have demonstrated some histopathological features in common with human pulmonary TB, these data should be considered carefully in the context of this disease. Further research is necessary to establish the most appropriate model for the study of TB, and to carry out a standard characterisation and score of pulmonary lesions.

Efficacy of heat-inactivated Mycobacterium bovis vaccine delivered to European badgers (Meles meles) through edible bait

Badgers (Meles meles) are a major tuberculosis (TB) reservoir in Europe, with the potential to transmit infection to cattle. Here we assessed whether a recently described oral tuberculosis vaccine based on heat-inactivated Mycobacterium bovis (HIMB), delivered as edible baits, can protect badgers from infection. Eight badgers were given individually five baits, each one consisting of a ball of peanut butter, natural peanut and oat flakes including a dose of the vaccine containing 5 × 107 colony-forming units. In parallel, a control group of seven badgers did not receive the vaccine. One month and a half later a second dose of the vaccine was offered to the vaccinated group. Ninety-four days after the second dose, all badgers were challenged with M. bovis (103 colony-forming units per animal) delivered endobronchially to the right middle lung lobe. Clinical, immunological, pathological and bacteriological variables were measured throughout the whole study to assess the efficacy of the vaccine. Two vaccinated animals showed high bacterial load of M. bovis and worsening of pathological lesions of TB. Conversely, the other six vaccinated animals showed slight improvement in bacterial load and pathology with respect to the control group. These results suggest that delivering the TB vaccine via food bait can partially protect wild badger populations, although vaccination can lead to either protection or tolerization, likely depending on the animal's immune status and general condition at the time of vaccination. Further optimization of the vaccination trial/strategy is needed to reduce the rate of tolerization, such as altering vaccine dose, number of doses, type of bait, use of adjuvants or route of administration.

Seroconversion against antigen MPB83 in badgers (Meles meles) vaccinated with multiple doses of BCG strain Sofia

Serological diagnosis of Mycobacterium bovis infection in badgers (Meles meles) has relied primarily on antibody recognition of MPB83, a sero-dominant antigen of M. bovis. Most vaccine studies in badgers to date have used the Bacille Calmette-Guerin (BCG) Danish strain, a low producer of MPB83. Due to a supply shortage of the BCG Danish strain, the BCG Sofia SL222 strain has been considered as an alternative vaccine. This strain is a high producer of MPB83 raising the possibility that vaccinated animals will test sero-positive in diagnostic assays that use this antigen. In this study we vaccinated a group of eleven badgers with BCG Sofia SL222 by injection via the intramuscular route and a booster vaccine dose was similarly delivered at 12 weeks and 64 weeks. Primary vaccination did not result in measured detection of antibodies against MPB83 in any badger during the first twelve weeks using serum or whole blood tested by the Dual Path Platform (DPP) VetTB, however, MPB83 antibodies were detected in a semi-quantitative ELISA assay. Following delivery of booster BCG at 12 weeks and 64 weeks, antibody responses against MPB83 were recorded in badgers using whole blood and serum on DPP VetTB and by ELISA. At all time points, vaccination was also associated with the in vitro production of gamma interferon (IFN-γ) following stimulation of lymphocytes with bovine and avian tuberculin (PPD) but not with MPB83 or M. bovis specific antigen CFP-10. The results indicate that serological diagnosis of tuberculosis using tests that target MPB83 may be compromised if badgers are repeatedly vaccinated with BCG Sofia.

Estimation of Bait Uptake by Badgers, Using Non-invasive Methods, in the Perspective of Oral Vaccination Against Bovine Tuberculosis in a French Infected Area

Although France is officially declared free of bovine tuberculosis (TB), Mycobacterium bovis infection is still observed in several regions in cattle and wildlife, including badgers (Meles meles). In this context, vaccinating badgers should be considered as a promising strategy for the reduction in M. bovis transmission between badgers and other species, and cattle in particular. An oral vaccine consisting of live Bacille Calmette–Guérin (BCG) contained in bait is currently under assessment for badgers, for which testing bait deployment in the field and assessing bait uptake by badgers are required. This study aimed to evaluate the bait uptake by badgers and determine the main factors influencing uptake in a TB-infected area in Burgundy, north-eastern France. The baits were delivered at 15 different setts located in the vicinity of 13 pastures within a TB-infected area, which has been subject to intense badger culling over the last decade. Pre-baits followed by baits containing a biomarker (Rhodamine B; no BCG vaccine) were delivered down sett entrances in the spring (8 days of pre-baiting and 4 days of baiting) and summer (2 days of pre-baiting and 2 days of baiting) of 2018. The consumption of the marked baits was assessed by detecting fluorescence, produced by Rhodamine B, in hair collected in hair traps positioned at the setts and on the margins of the targeted pastures. Collected hairs were also genotyped to differentiate individuals using 24 microsatellites markers and one sex marker. Bait uptake was estimated as the proportion of badgers consuming baits marked by the biomarker over all the sampled animals (individual level), per badger social group, and per targeted pasture. We found a bait uptake of 52.4% (43 marked individuals of 82 genetically identified) at the individual level and a mean of 48.9 and 50.6% at the social group and pasture levels, respectively. The bait uptake was positively associated with the presence of cubs (social group level) and negatively influenced by the intensity of previous trapping (social group and pasture levels). This study is the first conducted in France on bait deployment in a badger population of intermediate density after several years of intensive culling. The results are expected to provide valuable information toward a realistic deployment of oral vaccine baits to control TB in badger populations.

Protective immunity against tuberculosis in a free-living badger population vaccinated orally with Mycobacterium bovis Bacille Calmette-Guérin

Vaccination of badgers with Mycobacterium bovis Bacille Calmette-Guérin (BCG) has been shown to protect badgers against tuberculosis in experimental trials. During the 3-year County Kilkenny BCG vaccine field study, badgers were treated orally with placebo (100% in Zone A), BCG (100% in Zone C) or randomly assigned 50%: 50% treatment with BCG or placebo (Zone B). At the end of the study, 275 badgers were removed from the trial area and subjected to detailed post-mortem examination followed by histology and culture for M. bovis. Among these badgers, 83 (30.2%) were captured for the first time across the three zones, representing a non-treated proportion of the population. Analysis of the data based on the infection status of treated animals showed a prevalence of 52% (95% CI: 40%-63%) infection in Zone A (placebo), 39% (95% CI: 17%-64%) in Zone B (placebo) and 44% (95% CI: 20%-70%) in Zone B (BCG vaccinated) and 24% (95% CI: 14%-36%) in Zone C (BCG vaccinated). There were no statistically significant differences in the proportion of animals with infection involving the lung and thoracic lymph nodes, extra-thoracic infection or in the distribution and severity scores of histological lesions. Among the 83 non-treated badgers removed at the end of the study, the infection prevalence of animals in Zone A (prevalence = 46%, 95% CI: 32%-61%) and Zone B (prevalence = 44%, 95% CI: 23%-67%) was similar to the treated animals in these zones. However, in Zone C, no evidence of infection was found in any of the untreated badgers (prevalence = 0%, 95% CI: 0%-14%). This is consistent with an indirect protective effect in the non-vaccinated badgers leading to a high level of population immunity. The results suggest that BCG vaccination of badgers could be a highly effective means of reducing the incidence of tuberculosis in badger populations.

Mycobacterium bovis BCG Danish Strain 1331 isolated from a periarticular lesion in a domestic cat

A 7-year-old male neutered domestic shorthair outdoor cat was referred for chronic left forelimb lameness, which had been treated with intra-articular injections of triamcinolone acetonide. A soft tissue swelling around the elbow joint, extending from the distal humerus to the proximal ulna, was surgically explored and biopsy samples obtained. Mycobacterium bovis was cultured from samples from the soft tissue and bone. The mycobacteria from the media were killed and the DNA extracted and tested on a multiplex real-time PCR for the absence of specific genes and the presence of mycobacterial genus markers. The PCR revealed bacillus Calmette-Guérin Danish Strain 1331; this was also isolated from the prescapular lymph node, muscle and bone, obtained at post mortem examination. Badgers had been vaccinated with the bacillus Calmette-Guérin vaccine SSI (Statens Serum Institute) in the area where the cat lived, in the spring and autumn of the previous year. To the authors' knowledge, this is the first report of infection with M. bovis bacillus Calmette-Guérin Danish Strain 1331 in a domestic cat, potentially associated with annual vaccination of badgers in the proximity of the cat's home.

Estimating wildlife vaccination coverage using genetic methods

Vaccination is a useful approach for the control of disease in wildlife populations. However, its effectiveness is dependent in part on delivery to a sufficient proportion of the target population. Measuring the proportions of wild animal populations that have been vaccinated is challenging and so there is a need to develop robust approaches that can contribute to our understanding of the likely efficacy of wildlife vaccination campaigns. We used a modified capture mark recapture technique to estimate vaccine coverage in a wild population of European badgers (Meles meles) vaccinated by live-trapping and injecting with Bacillus Calmette-Guérin as part of a bovine tuberculosis control initiative in Wales, United Kingdom. Our approach used genetic matching of vaccinated animals to a sample of the wider population to estimate the percentage of badgers that had been vaccinated. Individual-specific genetic profiles were obtained using microsatellite genotyping of hair samples, which were collected directly from trapped and vaccinated badgers and non-invasively from the wider population using hair traps deployed at badger burrows (setts). With two nights of trapping at each sett in an annual campaign, an estimated 50 % (95 % confidence interval 40-60 %) of the badger population received at least one dose of vaccine in a single year. Using a simple population model this suggested that the proportion of the population that would have received at least one dose of vaccine over the course of the four year vaccination campaign was between 67 % and 83 %. This is the first attempt, outside of field trials, to quantify the level of vaccine coverage achieved by trapping and injecting badgers, which is currently the only option for delivering BCG vaccine to this species. The results therefore have specific application to bTB control policy and the novel approach may have wider value in wildlife management and research.

Development and Challenges in Animal Tuberculosis Vaccination

Vaccination with Bacillus Calmette-Guérin (BCG) constituted a major advance in the prevention of human tuberculosis (TB) in the beginning of the past century. BCG has also a clear potential for use in animals and, in particular, in the main domestic species subjected to TB control programs, cattle. Nowadays, the use of BCG vaccination against TB in cattle is not permitted by European Union legislation because BCG can induce a cellular immune response producing diagnostic interference in the eradication programs based on tuberculin single and comparative intradermal tests imposed worldwide. In this review we recall the history of TB vaccination as well as different vaccine trials and the response to vaccination in both domestic and wild animals. Promising potential inactivated vaccines are also reviewed. Research studies are mainly focused to improve vaccine efficacy, and at the same time to ensure its easy administration, safety and stability in the environment. Great challenges remain, particularly in terms of vaccine candidates and also in the acceptance of vaccination. Vaccination should be included in a strategic plan for integrated control of TB under a "one health" perspective, which also includes other measures such as improved biosafety on farms to avoid or decrease contact between domestic and wild animals or control of wildlife reservoirs to avoid overabundance that may favor infection maintenance.

Protective Effect of Oral BCG and Inactivated Mycobacterium bovis Vaccines in European Badgers (Meles meles) Experimentally Infected With M. bovis

In Europe, badgers (Meles meles) are recognized as major tuberculosis (TB) reservoir hosts with the potential to transmit infection to associated cattle herds. Recent studies in Spain have demonstrated that vaccination with a heat-inactivated Mycobacterium bovis vaccine (HIMB) successfully protects captive wild boar and red deer against progressive disease. The aim of this study was to evaluate the efficacy of two oral vaccines against TB in a badger model: the live-attenuated M. bovis bacillus Calmette-Guérin BCG vaccine (Danish strain) and a HIMB vaccine. Twenty-four badgers were separated in three treatment groups: oral vaccinated with live BCG (10⁸ CFU, n = 5), oral vaccinated with HIMB (10⁷ CFU, n = 7), and unvaccinated controls (n = 12). All badgers were experimentally infected with M. bovis (10³ CFU) by the endobronchial route targeting the right middle lung lobe. Throughout the study, clinical, immunological, pathological, and bacteriological parameters of infection were measured. Both vaccines conferred protection against experimental TB in badger, as measured by a reduction of the severity and lesion volumes. Based on these data, HIMB vaccination appears to be a promising TB oral vaccine candidate for badgers in endemic countries.

Detection of live M. bovis BCG in tissues and IFN-γ responses in European badgers (Meles meles) vaccinated by oropharyngeal instillation or directly in the ileum

Background

Oral vaccination with Mycobacterium bovis Bacille of Calmette and Guerin (BCG) has provided protection against M. bovis to badgers both experimentally and in the field. There is also evidence suggesting that the persistence of live BCG within the host is important for maintaining protection against TB. Here we investigated the capacity of badger inductive mucosal sites to absorb and maintain live BCG. The targeted mucosae were the oropharyngeal cavity (tonsils and sublingual area) and the small intestine (ileum).

Results

We showed that significant quantities of live BCG persisted within badger in tissues of vaccinated badgers for at least 8 weeks following oral vaccination with only very mild pathological features and induced the circulation of IFNγ-producing mononuclear cells. The uptake of live BCG by tonsils and drainage to retro-pharyngeal lymph nodes was repeatable in the animal group vaccinated by oropharyngeal instillation whereas those vaccinated directly in the ileum displayed a lower frequency of BCG detection in the enteric wall or draining mesenteric lymph nodes. No faecal excretion of live BCG was observed, including when BCG was delivered directly in the ileum.

Conclusions

The apparent local loss of BCG viability suggests an unfavorable gastro-enteric environment for BCG in badgers, which should be taken in consideration when developing an oral vaccine for use in this species.

A combined measure of tuberculous lesions for assessing the efficacy of vaccination against tuberculosis (Mycobacterium bovis) in European badgers (Meles meles) supports the 3Rs principle of reduction

BACKGROUND

An oral vaccine is a potential tool to tackle the reservoir of Mycobacterium bovis in European badgers (Meles meles), which contributes to tuberculosis of cattle in the British Isles. Inferences about vaccine protection against experimental challenge with M. bovis depend on the measurement of tuberculosis. Assessment of tuberculosis in larger species, such as badgers, is typically based on the tuberculous lesions visible at post-mortem examination and histopathology. We have developed a robust scoring system for tuberculous lesions by combining several parallel measures, which we call the "disease burden score" (DBS).

METHODS

Alternative scoring systems were compared within a regression analysis applied to observations from a total of 168 badgers from eight studies, including 107 badgers subjected to vaccination treatment and 61 non-vaccinated controls. The analysis included incidental observations that were recorded from each badger as potential covariate factors explaining some of the variation among animals sourced from the wild.

RESULTS

DBS was found to be the most accurate and reliable of the scoring systems compared. By taking account of significant covariates affecting disease, application of the DBS reduced residual variance by 22.9%. A previously used measure, based on assessment of visible lesions, was suboptimal due to non-uniform variance that increased with expected value, although square root transformation addressed this issue. The covariate model fitted to DBS included sex (males had higher DBS), weight (negatively associated with DBS) and immunological evidence of prior exposure to Mycobacterium avium (positively associated with DBS).

CONCLUSIONS

We identified improved measures of tuberculous disease derived from data already collected. We also demonstrated that the proper scaling of measurements of disease in such models is necessary and can be determined empirically. The covariates which were most strongly associated with the severity of disease are important in experimental studies involving outbred animals with variable background.

Purification and Characterisation of Badger IgA and Its Detection in the Context of Tuberculosis

European badgers are a wildlife reservoir of bovine tuberculosis in parts of Great Britain. Accurate diagnosis of tuberculosis in badgers is important for the development of strategies for the control of the disease. Sensitive serological tests for badger TB are needed for reasons such as cost and simplicity. Assay of mucosal IgA could be useful for diagnosing respiratory pathogens such as Mycobacterium bovis and for monitoring the response to mucosal vaccination. To develop an IgA assay, we purified secretory IgA from badger bile, identifying secretory component (SC), heavy chain (HC) and light chain (LC), at 66, 46 and 27 Kda, respectively, on the basis of size comparison with other species. Monoclonal antibodies (mAbs) were generated to purified IgA. We selected two for ELISA development. The detection limit of the IgA-specific mAbs was found to be approximately 20 ng/mL when titrated against purified badger bile. One monoclonal antibody specific for badger IgA was used to detect IgA in serum and tracheal aspirate with specificity to an immunodominant antigen of M. bovis. An M. bovis infection dose-dependent IgA response was observed in experimentally infected badgers. IgA was also detected by immunohistochemistry in the lungs of bTB-infected badgers. With further characterisation, these represent new reagents for the study of the IgA response in badgers.

Survival of Mycobacterium bovis BCG oral vaccine during transit through a dynamic in vitro model simulating the upper gastrointestinal tract of badgers

In developing an oral bait BCG vaccine against tuberculosis in badgers we wanted to understand the conditions of the gastrointestinal tract and their impact on vaccine viability. Conditions mimicking stomach and small-intestine caused substantial reduction in BCG viability. We performed in vivo experiments using a telemetric pH monitoring system and used the data to parameterise a dynamic in vitro system (TIM-1) of the stomach and small intestine. Some BCG died in the stomach compartment and through the duodenum and jejunum compartments. BCG survival in the stomach was greatest when bait was absent but by the time BCG reached the jejunum, BCG viability was not significantly affected by the presence of bait. Our data suggest that from a starting quantity of 2.85 ± 0.45 x 108 colony-forming units of BCG around 2 log10 may be killed before delivery to the intestinal lymphoid tissue. There are economic arguments for reducing the dose of BCG to vaccinate badgers orally. Our findings imply this could be achieved if we can protect BCG from the harsh environment of the stomach and duodenum. TIM-1 is a valuable, non-animal model with which to evaluate and optimise formulations to maximise BCG survival in the gastrointestinal tract.

New serological platform for detecting antibodies against Mycobacterium tuberculosis complex in European badgers

European badgers (Meles meles) have been identified as wildlife reservoirs for Mycobacterium bovis in the UK and Ireland, and may also have a role in the epidemiology of animal tuberculosis in other European regions. Thus, detection of M. bovis‐infected badgers may be required for the purposes of surveillance and monitoring of disease levels in infected populations. Current serological assays to detect M. bovis infection in live badgers, while rapid and inexpensive, show limited diagnostic sensitivity. Here we describe and evaluate new ELISA platforms for the recognition of the P22 multiprotein complex derived from the purified protein derivative (PPD) of M. bovis. The recognition of IgG against P22 multiprotein complex derived from PPD‐B was tested by ELISA in the serum of badgers from the UK, Ireland and Spain. TB infection in the badgers was indicated by the presence of M. bovis in tissues by culture and histology at post‐mortem examination and TB‐free status was established by repeated negativity in the interferon γ release assay (IGRA). In experimentally infected badgers, humoral antibody responses against P22 developed within 45 days post‐infection. The ELISA tests showed estimated sensitivity levels of 74–82% in experimentally and naturally infected badgers with specificities ranging from 75% to 100% depending on the badger population tested. The P22 multi‐antigen based ELISAs provide a sensitive and specific test platform for improved tuberculosis surveillance in badgers.

Bait uptake by wild badgers and its implications for oral vaccination against tuberculosis

The deployment of baits containing vaccines or toxins has been used successfully in the management of wildlife populations, including for disease control. Optimisation of deployment strategies seeks to maximise uptake by the targeted population whilst ensuring cost-effectiveness. Tuberculosis (TB) caused by infection with Mycobacterium bovis affects a broad range of mammalian hosts across the globe, including cattle, wildlife and humans. The control of TB in cattle in the UK and Republic of Ireland is hampered by persistent infection in European badgers (Meles meles). The present study aimed to determine the best strategy for maximising uptake of an oral vaccine by wild badgers, using a surrogate novel bait deployed at 40 badger social groups. Baits contained a blood-borne biomarker (Iophenoxic Acid, IPA) in order to measure consumption in badgers subsequently cage trapped at targeted setts. Evidence for the consumption of bait was found in 83% (199/240) of captured badgers. The probability that badgers had consumed at least one bait (IPA >10 μg ml-1) was significantly higher following deployment in spring than in summer. Lower uptake amongst social groups where more badgers were captured, suggested competition for baits. The probability of bait consumption was significantly higher at groups where main and outlier setts were provided with baits than at those where outliers were present but not baited. Badgers captured 10-14 days post bait feeding had significantly higher levels of bait uptake compared to those caught 24-28 days later. Uptake rates did not vary significantly in relation to badger age and whether bait was placed above ground or down setts. This study suggests that high levels of bait uptake can be achieved in wild badger populations and identifies factors influencing the potential success of different deployment strategies. The implications for the development of an oral badger vaccine are discussed.

Efficacy and Safety of BCG Vaccine for Control of Tuberculosis in Domestic Livestock and Wildlife

Bovine tuberculosis (TB) continues to be an intractable problem in many countries, particularly where "test and slaughter" policies cannot be implemented or where wildlife reservoirs of Mycobacterium bovis infection serve as a recurrent source of infection for domestic livestock. Alternative control measures are urgently required and vaccination is a promising option. Although the M. bovis bacille Calmette-Guérin (BCG) vaccine has been used in humans for nearly a century, its use in animals has been limited, principally as protection against TB has been incomplete and vaccination may result in animals reacting in the tuberculin skin test. Valuable insights have been gained over the past 25 years to optimise protection induced by BCG vaccine in animals and in the development of tests to differentiate infected from vaccinated animals (DIVA). This review examines factors affecting the efficacy of BCG vaccine in cattle, recent field trials, use of DIVA tests and the effectiveness of BCG vaccine in other domestic livestock as well as in wildlife. Oral delivery of BCG vaccine to wildlife reservoirs of infection such as European badgers, brushtail possums, wild boar, and deer has been shown to induce protection against TB and could prove to be a practical means to vaccinate these species at scale. Testing of BCG vaccine in a wide range of animal species has indicated that it is safe and vaccination has the potential to be a valuable tool to assist in the control of TB in both domestic livestock and wildlife.

Immunological responses of European badgers (Meles Meles) to infection with Mycobacterium bovis

Mycobacterium bovis is the main cause of bovine tuberculosis and its eradication is proving difficult in many countries because of wildlife reservoirs, including European badgers (Meles meles) in the UK Ireland. Following the development of badger specific immunological reagents, many studies have shown that some aspects of the cellular and serological immune responses of badgers to virulent M. bovis and the attenuated M. bovis BCG (Bacille of Calmette and Guérin) strain are similar to those seen in other animal hosts infected with M. bovis. However, badgers also appear to have developed specific immunological responses to M. bovis infection which may be associated with mild inflammatory responses. Badgers may therefore represent an interesting natural host for M. bovis that can provide a more thorough understanding of efficient immunological responses to tuberculosis.

Oral Vaccination with Heat-Inactivated Mycobacterium bovis Does Not Interfere with the Antemortem Diagnostic Techniques for Tuberculosis in Goats

Vaccination against tuberculosis (TB) is prohibited in cattle or other species subjected to specific TB eradication campaigns, due to the interference that it may cause with the official diagnostic tests. However, immunization with a heat-inactivated (HI) Mycobacterium bovis vaccine via the oral route has been suggested to overcome this issue. In this study, the main goal was to assess the interference of the HI vaccine by different routes of administration using a previous vaccination and re-vaccination (boosting) protocol. TB-free kid goats were divided into three groups: oral (n = 16), intramuscular (IM; n = 16), and control (n = 16). Results showed that there was a significant difference in the percentage of animals positive to the single intradermal test (SIT) and blood based interferon-gamma release assay (IGRA) caused by vaccination when performed in the IM group compared to the oral group (p < 0.001). Nevertheless, no positivity to the SIT or IGRA test was observed in orally vaccinated goats regardless of the different interpretation criteria applied. None of the groups presented positive antibody titers using an in-house ELISA and samples collected 2 months after the boost. These results suggest the potential usefulness of the HI vaccine by the oral route in goats to minimize the interference on diagnostic tests (skin and IGRA tests) and reducing the necessity of defined antigens to replace the traditional purified protein derivatives for diagnosis. Finally, the results pave the way to future efficacy studies in goats using different routes of HI vaccination.

Field evaluation of candidate baits for oral delivery of BCG vaccine to European badgers, Meles meles

The control of tuberculosis (TB) in cattle in the UK and Ireland is compromised by transmission of Mycobacterium bovis to cattle from the European badger (Meles meles), which acts as a wildlife reservoir. Vaccination of badgers could potentially contribute to TB control but the only licensed vaccine is injectable BadgerBCG which requires the live-capture of badgers. Current research is aimed at developing an oral TB vaccine (where vaccine is contained within bait) that is intended to be more cost-effective to deploy over large areas. In order to identify a lead product, candidate baits identified from captive badger studies were evaluated in three successive bait screening studies with wild badgers. A fourth field study, using the lead candidate bait and biomarkers, investigated the effectiveness of different carriers for their potential to deliver liquid payloads (vaccine surrogate). In each field study, bait disappearance was monitored daily for ten days and remote video surveillance was used to determine preference (i.e. the order in which baits were taken). In the carrier study, biomarkers were used to determine what proportion of subsequently trapped badgers had ingested the bait and the vaccine-carrier biomarker payload. Across all four studies, 79% (3397/4330) of baits were taken by badgers although the number varied significantly by badger social group and bait type. In all studies, bait disappearance increased over time, with 75-100% of baits being taken by day ten. In the carrier study, 75% (9/12) of trapped badgers tested positive for at least one of the biomarkers and the type of carrier did not influence bait attractiveness. Together with data from complementary laboratory and captive animal studies, this study identified a highly attractive and palatable bait (peanut-based paste bait; PT) and vaccine-carrier (hydrogenated peanut oil; HPO) combination with the potential to deliver a liquid vaccine to wild badgers.

Oral Vaccination of Free-Living Badgers (Meles meles) with Bacille Calmette Guérin (BCG) Vaccine Confers Protection against Tuberculosis

A field trial was conducted to investigate the impact of oral vaccination of free-living badgers against natural-transmitted Mycobacterium bovis infection. For a period of three years badgers were captured over seven sweeps in three zones and assigned for oral vaccination with a lipid-encapsulated BCG vaccine (Liporale-BCG) or with placebo. Badgers enrolled in Zone A were administered placebo while all badgers enrolled in Zone C were vaccinated with BCG. Badgers enrolled in the middle area, Zone B, were randomly assigned 50:50 for treatment with vaccine or placebo. Treatment in each zone remained blinded until the end of the study period. The outcome of interest was incident cases of tuberculosis measured as time to seroconversion events using the BrockTB Stat-Pak lateral flow serology test, supplemented with post-mortem examination. Among the vaccinated badgers that seroconverted, the median time to seroconversion (413 days) was significantly longer (p = 0.04) when compared with non-vaccinated animals (230 days). Survival analysis (modelling time to seroconversion) revealed that there was a significant difference in the rate of seroconversion between vaccinated and non-vaccinated badgers in Zones A and C throughout the trial period (p = 0.015). For badgers enrolled during sweeps 1–2 the Vaccine Efficacy (VE) determined from hazard rate ratios was 36% (95% CI: -62%– 75%). For badgers enrolled in these zones during sweeps 3–6, the VE was 84% (95% CI: 29%– 97%). This indicated that VE increased with the level of vaccine coverage. Post-mortem examination of badgers at the end of the trial also revealed a significant difference in the proportion of animals presenting with M. bovis culture confirmed lesions in vaccinated Zone C (9%) compared with non-vaccinated Zone A (26%). These results demonstrate that oral BCG vaccination confers protection to badgers and could be used to reduce incident rates in tuberculosis-infected populations of badgers.

The Effect of Oral Vaccination with Mycobacterium bovis BCG on the Development of Tuberculosis in Captive European Badgers (Meles meles)

The European badger (Meles meles) is a reservoir host of Mycobacterium bovis and responsible for a proportion of the tuberculosis (TB) cases seen in cattle in the United Kingdom and Republic of Ireland. An injectable preparation of the bacillus Calmette-Guérin (BCG) vaccine is licensed for use in badgers in the UK and its use forms part of the bovine TB eradication plans of England and Wales. However, there are practical limitations to the widespread application of an injectable vaccine for badgers and a research priority is the development of an oral vaccine deliverable to badgers in bait. Previous studies reported the successful vaccination of badgers with oral preparations of 10⁸ colony forming units (CFU) of both Pasteur and Danish strains of BCG contained within a lipid matrix composed of triglycerides of fatty acids. Protection against TB in these studies was expressed as a reduction in the number and apparent progression of visible lesions, and reductions in the bacterial load and dissemination of infection. To reduce the cost of an oral vaccine and reduce the potential for environmental contamination with BCG, it is necessary to define the minimal efficacious dose of oral BCG for badgers. The objectives of the two studies reported here were to compare the efficacy of BCG Danish strain in a lipid matrix with unformulated BCG given orally, and to evaluate the efficacy of BCG Danish in a lipid matrix at a 10-fold lower dose than previously evaluated in badgers. In the first study, both BCG unformulated and in a lipid matrix reduced the number and apparent progression of visible lesions and the dissemination of infection from the lung. In the second study, vaccination with BCG in the lipid matrix at a 10-fold lower dose produced a similar outcome, but with greater intra-group variability than seen with the higher dose in the first study. Further research is needed before we are able to recommend a final dose of BCG for oral vaccination of badgers against TB or to know whether oral vaccination of wild badgers with BCG will significantly reduce transmission of the disease.

Testing of a palatable bait and compatible vaccine carrier for the oral vaccination of European badgers (Meles meles) against tuberculosis

The oral vaccination of wild badgers (Meles meles) with live Bacillus Calmette-Guérin (BCG) is one of the tools being considered for the control of bovine tuberculosis (caused by Mycobacterium bovis) in the UK. The design of a product for oral vaccination requires that numerous, and often competing, conditions are met. These include the need for a highly palatable, but physically stable bait that will meet regulatory requirements, and one which is also compatible with the vaccine formulation; in this case live BCG. In collaboration with two commercial bait companies we have developed a highly attractive and palatable bait recipe designed specifically for European badgers (Meles meles) that meets these requirements. The palatability of different batches of bait was evaluated against a standardised palatable control bait using captive badgers. The physical properties of the bait are described e.g. firmness and colour. The microbial load in the bait was assessed against European and US Pharmacopoeias. The bait was combined with an edible vaccine carrier made of hydrogenated peanut oil in which BCG vaccine was stable during bait manufacture and cold storage, demonstrating <0.5 log₁₀ reduction in titre after 117weeks' storage at -20°C. BCG stability in bait was also evaluated at +4°C and under simulated environmental conditions (20°C, 98% Relative Humidity; RH). Finally, iophenoxic acid biomarkers were utilised as a surrogate for the BCG vaccine, to test variants of the vaccine-bait design for their ability to deliver biomarker to the gastrointestinal tract of individual animals. These data provide the first detailed description of a bait-vaccine delivery system developed specifically for the oral vaccination of badgers against Mycobacterium bovis using live BCG.

Tackling tuberculosis: Insights from an international TB Summit in London

Tuberculosis (TB) poses a grave predicament to the world as it is not merely a scientific challenge but a socio-economic burden as well. A prime cause of mortality in human due to an infectious disease; the malady and its cause, Mycobacterium tuberculosis have remained an enigma with many questions that remain unanswered. The ability of the pathogen to survive and switch between varied physiological states necessitates a protracted therapeutic regimen that exerts an excessive strain on low-resource countries. To complicate things further, there has been a significant rise of antimicrobial resistance. Existing control measures, including treatment regimens have remained fairly uniform globally for at least half a century and require reinvention. Overcoming the societal and scientific challenges requires an increase in dialog to identify key regions that need attention and effective partners with whom successful collaborations can be fostered. In this report, we explore the discussions held at the International TB Summit 2015 hosted by EuroSciCon, which served as an excellent platform for researchers to share their recent findings. Ground-breaking results require outreach to affect policy design, governance and control of the disease. Hence, we feel it is important that meetings such as these reach a wider, global audience.

Vaccination against tuberculosis in badgers and cattle: an overview of the challenges, developments and current research priorities in Great Britain

Bovine tuberculosis (TB) is a significant threat to the cattle industry in England and Wales. It is widely acknowledged that a combination of measures targeting both cattle and wildlife will be required to eradicate bovine TB or reduce its prevalence until European official freedom status is achieved. Vaccination of cattle and/or badgers could contribute to bovine TB control in Great Britain, although there are significant gaps in our knowledge regarding the impact that vaccination would actually have on bovine TB incidence. Laboratory studies have demonstrated that vaccination with BCG can reduce the progression and severity of TB in both badgers and cattle. This is encouraging in terms of the prospect of a sustained vaccination programme achieving reductions in disease prevalence; however, developing vaccines for tackling the problem of bovine TB is challenging, time-consuming and resource-intensive, as this review article sets out to explain.

Association of quantitative interferon-γ responses with the progression of naturally acquired Mycobacterium bovis infection in wild European badgers (Meles meles)

Bovine tuberculosis is one of the biggest challenges facing cattle farming in Great Britain. European badgers (Meles meles) are a reservoir host for the causal agent, Mycobacterium bovis. There have been significant recent advances in diagnostic testing for tuberculosis in humans, cattle and badgers, with the development of species-specific assays for interferon-γ (IFN-γ), an important cytokine in tuberculous infections. Using data collected from longitudinal studies of naturally infected wild badgers, we report that the magnitude of the IFN-γ response to M. bovis antigens at the disclosing test event was positively correlated with subsequent progression of disease to a seropositive or excreting state. In addition, we show that the magnitude of the IFN-γ response, despite fluctuation, declined with time after the disclosing event for all badgers, but remained significantly higher in those animals with evidence of disease progression. We discuss how our findings may be related to the immunopathogenesis of natural M. bovis infection in badgers.

Overview of vaccination trials for control of tuberculosis in cattle, wildlife and humans

Vaccination is a key strategy for control of tuberculosis (TB), and considerable progress has been made in the past 5 years to develop improved vaccines for humans and animals, differentiate vaccinated animals from those infected with Mycobacterium bovis and deliver vaccines to wildlife. Studies have moved from testing vaccines in small animal models to clinical trials in humans and from experimental challenge studies in cattle and wildlife to evaluation of vaccines in the field. Candidate vaccines undergoing testing in humans include live mycobacterial vaccines to replace bacille Calmette Guérin (BCG), subunit vaccines (virus vector or protein) to boost BCG and therapeutic vaccines used as an adjunct to chemotherapy. In cattle, a number of diagnostic tests have been developed and successfully tested for differentiating infected from vaccinated animals, which will facilitate the use of BCG vaccine in cattle. Encouraging results have been obtained from recent field trials in cattle using BCG vaccine to protect against natural exposure to M. bovis. To date, no subunit TB vaccines have induced improved protection compared with that for BCG, but prime-boost combinations of BCG with DNA, protein or virus-vectored vaccines have induced better protection than BCG vaccine alone. Development of an oral bait BCG formulation has demonstrated the practicality of delivering TB vaccines to wildlife. Oral BCG preparations have induced protection against experimental challenge of M. bovis in possums, badgers, wild boar and white-tailed deer and against natural exposure to M. bovis in possums. Recent progress in TB vaccine development has provided much impetus for their future use.

Veterinary and human vaccine evaluation methods

Despite the universal importance of vaccines, approaches to human and veterinary vaccine evaluation differ markedly. For human vaccines, vaccine efficacy is the proportion of vaccinated individuals protected by the vaccine against a defined outcome under ideal conditions, whereas for veterinary vaccines the term is used for a range of measures of vaccine protection. The evaluation of vaccine effectiveness, vaccine protection assessed under routine programme conditions, is largely limited to human vaccines. Challenge studies under controlled conditions and sero-conversion studies are widely used when evaluating veterinary vaccines, whereas human vaccines are generally evaluated in terms of protection against natural challenge assessed in trials or post-marketing observational studies. Although challenge studies provide a standardized platform on which to compare different vaccines, they do not capture the variation that occurs under field conditions. Field studies of vaccine effectiveness are needed to assess the performance of a vaccination programme. However, if vaccination is performed without central co-ordination, as is often the case for veterinary vaccines, evaluation will be limited. This paper reviews approaches to veterinary vaccine evaluation in comparison to evaluation methods used for human vaccines. Foot-and-mouth disease has been used to illustrate the veterinary approach. Recommendations are made for standardization of terminology and for rigorous evaluation of veterinary vaccines.

Modelling the impact of vaccination on tuberculosis in badgers

Tuberculosis (TB) in livestock, caused by Mycobacterium bovis, persists in many countries. In Britain, efforts to control TB through the culling of badgers (Meles meles), the principal wildlife host, have so far been unsuccessful, and there is significant interest in vaccination of badgers as an alternative or complementary strategy [corrected]. Using a simulation model, we show that where TB is self-contained within the badger population and there are no external sources of infection, limited-duration vaccination at a high level of efficacy can reduce or even eradicate TB from the badger population. However, where sources of external infection persist, benefits in TB reduction in badgers can only be achieved by ongoing, annual vaccination. Vaccination is likely to be most effective as part of an integrated disease management strategy incorporating a number of different approaches across the entire host community.

Non-tuberculous mycobacteria in wild boar (Sus scrofa) from Southern Spain: epidemiological, clinical and diagnostic concerns

Non-tuberculous mycobacteria (NTM) are widely distributed in the environment, particularly in wet soil, marshland, rivers or streams, but also are causative agents of a wide variety of infections in animals and humans. Little information is available regarding the NTM prevalence in wildlife and their effects or significance in the bovine tuberculosis (bTB) epidemiology and diagnosis. This research shows the most frequently NTM isolated in lymph nodes of wild boar (Sus scrofa) from southern Spain, relating the NTM presence with the individual characteristics, the management of animals and the possible misdiagnosis of Mycobacterium bovis in concurrent infections. A total of 219 NTM isolates were obtained from 1249 wild boar mandibular lymph nodes sampled between 2007 and 2011. All but 75 isolates were identified by the PCR-restriction analysis-hsp65, and a partial sequencing of the 16S rDNA was carried out to identify the rest of the isolates. Results showed that Mycobacterium chelonae was the most frequently isolated NTM specie (133 isolates, 60.7%), followed by Mycobacterium avium (24 isolates, 11%). No relation was found regarding sex, body condition and management, but M. chelonae was more frequently detected in adults, whereas M. avium was more prevalent in subadults. The high NTM prevalence observed in the studied wild boar populations could make difficult the bTB diagnostic.

Evaluation of a method to detect Mycobacterium bovis in air samples from infected Eurasian badgers (Meles meles) and their setts

Environmental air sampling was evaluated as a method to detect the presence of M. bovis in the vicinity of infected badgers and their setts. Airborne particles were collected on gelatine filters using a commercially available air sampling instrument and tested for the presence of M. bovis using bacteriological culture and real-time PCR. The sensitivity of bacteriological culture was broadly similar to that of real-time PCR when testing samples artificially spiked with M. bovis. Sampling was undertaken from directly under the muzzles of badgers which had been experimentally infected with M. bovis (37 samples), within enclosures housing the experimentally infected animals (50 samples), and in the vicinity of setts with resident infected wild badgers (52 samples). The methods employed did not detect M. bovis from either infected badgers or artificial or natural setts known to contain infected animals. However, samples taken at four of the six natural setts were positive for Mycobacterium gordonae.

BCG vaccination reduces risk of tuberculosis infection in vaccinated badgers and unvaccinated badger cubs

Wildlife is a global source of endemic and emerging infectious diseases. The control of tuberculosis (TB) in cattle in Britain and Ireland is hindered by persistent infection in wild badgers (Meles meles). Vaccination with Bacillus Calmette-Guérin (BCG) has been shown to reduce the severity and progression of experimentally induced TB in captive badgers. Analysis of data from a four-year clinical field study, conducted at the social group level, suggested a similar, direct protective effect of BCG in a wild badger population. Here we present new evidence from the same study identifying both a direct beneficial effect of vaccination in individual badgers and an indirect protective effect in unvaccinated cubs. We show that intramuscular injection of BCG reduced by 76% (Odds ratio = 0.24, 95% confidence interval (CI) 0.11-0.52) the risk of free-living vaccinated individuals testing positive to a diagnostic test combination to detect progressive infection. A more sensitive panel of tests for the detection of infection per se identified a reduction of 54% (Odds ratio = 0.46, 95% CI 0.26-0.88) in the risk of a positive result following vaccination. In addition, we show the risk of unvaccinated badger cubs, but not adults, testing positive to an even more sensitive panel of diagnostic tests decreased significantly as the proportion of vaccinated individuals in their social group increased (Odds ratio = 0.08, 95% CI 0.01-0.76; P = 0.03). When more than a third of their social group had been vaccinated, the risk to unvaccinated cubs was reduced by 79% (Odds ratio = 0.21, 95% CI 0.05-0.81; P = 0.02).

Factors affecting European badger (Meles meles) capture numbers in one county in Ireland

Understanding factors affecting the number of badgers captured at and around badger setts (burrows) is of considerable applied importance. These factors could be used to estimate probable badger densities for bovine tuberculosis (bTB) control and also for monitoring badger populations from a conservation perspective. Furthermore, badger management and vaccination programs would benefit by increasing the probability of efficiently capturing the target badger populations. Within this context, it was investigated whether badger capture numbers can be estimated from field signs and previous capture histories. Badger capture records (initial and repeated capture numbers at a sett) from a large-scale removal program (405 km(2), 643 setts) were used. Univariable count models indicated that there were a number of significant potential predictors of badger numbers, during initial capture attempts. Using a multivariable zero-inflated Poisson (ZIP) model of initial captures we found that badger capture numbers were significantly affected by sett type, season, year, and the number of sett entrances in active use. Badger capture numbers were also affected by the total previous catch during repeated capture events and by the number of previous capture attempts. There was a significant negative trend in badger captures across events. Measures of the ability of these models to estimate badger captures suggested that the models might be useful in estimating badger numbers across a population; however the confidence intervals associated with these predictions were large.

Bovine tuberculosis vaccine research: historical perspectives and recent advances

The emergence of wildlife reservoirs of Mycobacterium bovis infection in cattle as well as increased inter-regional trade with associated spread of M. bovis has led to renewed interest in the use of vaccines for the control of bovine tuberculosis (TB). Field efficacy trials performed in the early 20th century demonstrated the partial effectiveness of bacilli Calmette-Guerin (BCG) for the control of bovine TB. Recent experimental trials with cattle have demonstrated that: (1) subunit vaccines may boost immunity elicited by BCG in cattle, (2) T cell central memory immune responses evoked by protective vaccines correlate with protection upon subsequent M. bovis challenge, (3) BCG is particularly protective when administered to neonates, and (4) differentiation of infected from vaccinated animals (DIVA) is feasible in cattle using in vitro or in vivo methods. In regards to wildlife reservoirs, the efficacy of BCG delivered orally has been demonstrated for brushtail possums (in field trials) as well as Eurasian badgers, wild boar, and white-tailed deer (each in experimental challenge studies). Vaccine delivery to wildlife reservoirs will primarily be oral, although a parenteral route is being deployed for badgers in England. Vaccine efficacy trials, both experimental challenge and field studies, with cattle and their wildlife reservoirs represent a primary example of the one health approach, with outcomes relevant for both veterinary and medical applications.

An ecological and comparative perspective on the control of bovine tuberculosis in Great Britain and the Republic of Ireland

Disease ecology involves a systematic approach to understanding the interactions and evolution of host-pathogen systems at the population level, and is essential for developing a comprehensive understanding of the reasons for disease persistence and the most likely means of control. This systems or ecological approach is being increasingly recognised as a progressive method in disease control and is exploited in diverse fields ranging from obesity management in humans to the prevention of infectious disease in animal populations. In this review we discuss bovine tuberculosis (bTB) in Great Britain (GB) within a disease ecology context, and suggest how a comparative ecological perspective helps to reconcile apparent conflicts with the evidence on the effectiveness of badger culling to assist in the control of bTB in GB and the Republic of Ireland (ROI). Our examination shows that failure of past measures to control bTB and the disparity in outcomes of badger culling experiments are the result of a complex relationship amongst the agent, host and environment, i.e. the episystem, of bTB. Here, we stress the role of distinctive bTB episystems and badger culling trial design in the ambiguity and resulting controversy associated with badger culling in GB and ROI. We argue this episystem perspective on bTB control measures in cattle and badger populations provides a useful and informative perspective on the design and implementation of future bTB management in GB, particularly at a time when both scientific and lay communities are concerned about the ongoing epidemic, the cost of current control measures and the execution of future control procedures.

BCG vaccination of neonatal calves: potential roles for innate immune cells in the induction of protective immunity

Bovine tuberculosis is a disease of increasing incidence in the UK causing major economic losses and with significant impact on bovine and, potentially human health: the causative agent Mycobacterium bovis is a zoonotic pathogen. Neonatal vaccination with the attenuated M. bovis Bacille Calmette Guerin (BCG) vaccine confers a significant degree of protection in cattle, and is a widely used control strategy for human TB. The adaptive immune system is relatively immature in neonates and increased numbers of innate effector cells present in young animals and human infants may compensate for this, enabling effective immune responses to vaccination. Natural killer cells and subsets of γδ TCR+ T lymphocytes secrete high levels of interferon gamma and can interact with antigen presenting cells to promote both innate and adaptive immune responses. These cell populations may be pivotal in determining immune bias following neonatal vaccination with BCG.