Pathology of naturally occurring bovine tuberculosis in England and Wales

The aim of this study was to obtain a contemporary data set of pathology in tuberculin reactor and in-contact cattle in England and Wales. Four hundred animals (200 reactors and 200 in-contacts) from 242 farms located in 14 counties in Western England and Wales were examined. The mean number of lymph nodes (LNs) with tuberculosis (TB)-like lesions per TB-confirmed animal was 1.7 in reactors and 1.5 in in-contact animals. Tuberculous lesions in both reactor and in-contact animals were most commonly observed in the LNs of the thorax, followed by the head and abdomen, particularly the mediastinal, retropharyngeal and tracheobronchial LNs. Twenty-five reactors had macroscopic lesions in the palatine tonsils. Among TB-confirmed cattle, 27% of reactors and 9% of in-contact animals had gross TB-like lesions in the lungs, particularly in the caudal lobes. Gross lesions that were not TB-confirmed were parasitic granulomas (45%), bacterial or mycotic club-forming pyogranulomas (27%) and bacterial abscesses (23%). Diagnostic sensitivity was maximised when bacteriology and histopathology were used concurrently. Stage IV granulomas, alone or in combination with other stages, constituted 63% of lesions, while 16% of lesions were stage I/II granulomas. Caseous necrosis and calcification were common features of the granulomas encountered in natural Mycobacterium bovis infections, even with pathology limited to a small number of sites. Granulomas often covered large areas of histological sections and typically contained only small numbers of acid fast bacilli.

Assessment of cross-reactivity between Mycobacterium bovis and M. kansasii ESAT-6 and CFP-10 at the T-cell epitope level

Cross-reactivity between Mycobacterium kansasii ESAT-6 and CFP-10 homologues and their M. bovis counterparts can confound the interpretation of immunodiagnostic tests for tuberculosis. M. kansasii is a nontuberculous mycobacterial species cultured from skin test-positive cattle in Great Britain. Using peptides derived from M. bovis and M. kansasii ESAT-6 and CFP-10 regions that differ between these species, we investigated the species specificity and cross-reactivity at the level of individual bovine T-cell epitopes. Our results demonstrated that all peptides tested are fully cross-reactive, with the exception of one ESAT-6-derived peptide that harbored an M. bovis-specific epitope(s) when it was recognized in the context of bovine leukocyte antigen (BoLA)-DQ but that was cross-reactive with its M. kansasii homologues when it was restricted by BoLA-DR. This observation further highlights that prediction of species specificity by comparing sequence identity/homology alone is not sufficient and that individuals with diverse major histocompatibility complex constellations need to be tested to characterize the cross-reactivity or species specificity of peptide-based reagents.

Rapid detection of Mycobacterium bovis DNA in cattle lymph nodes with visible lesions using PCR

Background

We have evaluated a sensitive screening assay for Mycobacterium tuberculosis (MTB) complex organisms and a specific assay for detecting Mycobacterium bovis DNA in lymph nodes taken from cattle with evidence of bovine tuberculosis. Underlying these series of experiments was the need for a versatile DNA extraction protocol which could handle tissue samples and with the potential for automation.

The target for the screening assay was the multi-copy insertion element IS1081, present in 6 copies in the MTB complex. For confirmation of M. bovis we used primers flanking a specific deletion in the genome of M. bovis known as region of difference 4 (RD4). The sensitivity and specificity of these PCRs has been tested on genomic DNA from MTB complex reference strains, mycobacteria other than tuberculosis (MOTT), spiked samples and on clinical material.

Results

The minimum detection limits of the IS1081 method was < I genome copy and for the RD4 PCR was 5 genome copies. Both methods can be readily adapted for quantitative PCR with the use of SYBR Green intercalating dye on the RotorGene 3000 platform (Corbett Research).

Initial testing of field samples of bovine lymph nodes with visible lesions (VL, n = 109) highlighted two shortfalls of the molecular approach. Firstly, comparison of IS1081 PCR with the "gold standard" of culture showed a sensitivity of approximately 70%. The sensitivity of the RD4 PCR method was 50%. Secondly, the success rate of spoligotyping applied directly to clinical material was 51% compared with cultures. A series of further experiments indicated that the discrepancy between sensitivity of detection found with purified mycobacterial DNA and direct testing of field samples was due to limited mycobacterial DNA recovery from tissue homogenates rather than PCR inhibition. The resilient mycobacterial cell wall, the presence of tissue debris and the paucibacillary nature of some cattle VL tissue may all contribute to this observation. Any of these factors may restrict application of other more discriminant typing methods.

A simple means of increasing the efficiency of mycobacterial DNA recovery was assessed using a further pool of 95 cattle VL. Following modification of the extraction protocol, detection rate with the IS1081 and RD4 methods increased to 91% and 59% respectively.

Conclusion

The IS1081 PCR is a realistic screening method for rapid identification of positive cases but the sensitivity of single copy methods, like RD4 and also of spoligotyping will need to be improved to make these applicable for direct testing of tissue extracts.

Vaccination of cattle with Danish and Pasteur strains of Mycobacterium bovis BCG induce different levels of IFNgamma post-vaccination, but induce similar levels of protection against bovine tuberculosis

A number of studies have demonstrated significant protection of cattle against bovine tuberculosis following vaccination with the Pasteur strain of Mycobacterium bovis bacille Calmete-Guerin (BCG). However, it is unclear if other daughter strains of BCG are as effective, which is an important issue to resolve for a variety of regulatory compliance issues. This study compared the protective immune responses to bovine tuberculosis induced in cattle vaccinated with BCG Danish with those induced by BCG Pasteur. Groups of calves (n=10) were vaccinated with 10(6) colony forming units (CFU) BCG Pasteur prepared from a fresh liquid culture, 10(6) CFU BCG Danish prepared from a fresh liquid culture or 0.4 mg of reconstituted freeze-dried culture of BCG Danish. Another group (n=10) served as non-vaccinated controls. BCG Pasteur induced significantly higher and more sustained levels of bovine purified protein derivative (PPD)-specific gamma interferon (IFN-gamma) in whole-blood cultures following vaccination compared to either fresh culture BCG Danish or freeze-dried BCG Danish. Vaccination with a fresh culture of BCG Pasteur, fresh culture BCG Danish and freeze-dried BCG Danish gave a significant enhancement in three, four and three pathological and microbiological parameters of protection, respectively, compared to the non-vaccinated group. These results demonstrate the Danish strain of BCG is a viable alternative to BCG Pasteur for vaccination of cattle as both strains had similar efficacy and there was little difference between freshly cultured and freeze-dried formulation of BCG Danish. The results also show that post-vaccination antigen-specific IFN-gamma levels in whole blood is not always a reliable indicator of protection against a subsequent virulent challenge.

Cluster of human tuberculosis caused by Mycobacterium bovis: evidence for person-to-person transmission in the UK

BACKGROUND

Despite a recent resurgence in the incidence of bovine tuberculosis in UK cattle herds, no associated rise in the number of cases in man has been noted. Disease due to human Mycobacterium bovis infection usually occurs in older patients, in whom drinking unpasteurised milk in the past is the probable source of infection. Person-to-person transmission is very rare.

METHODS

After identification of two epidemiologically-linked cases of human M bovis infection through routine laboratory and surveillance activities, all patients identified with M bovis infection in the Midlands from 2001-05 (n=20) were assessed by DNA fingerprinting (MIRU-VNTR and spoligotyping), with additional interviews for patients with a clustered strain.

FINDINGS

A cluster of six cases was identified. All clustered cases were young and UK-born; five patients had pulmonary disease, and one patient died due to M bovis meningitis, with four patients possessing factors predisposing to tuberculosis. All patients had common social links through visits to bars in two different areas. With the exception of the first case, there was an absence of zoonotic links or consumption of unpasteurised dairy products, suggesting that person-to-person transmission had occurred.

INTERPRETATION

This report of several instances of M bovis transmission between people in a modern urban setting emphasises the need to maintain control measures for human and bovine tuberculosis. Transmission and subsequent disease was probably due to a combination of host and environmental factors. Prospective surveillance and DNA fingerprinting identified the cluster, enabling health protection teams to set up control measures and prevent further transmission.

Genome plasticity of BCG and impact on vaccine efficacy

To understand the evolution, attenuation, and variable protective efficacy of bacillus Calmette-Guérin (BCG) vaccines, Mycobacterium bovis BCG Pasteur 1173P2 has been subjected to comparative genome and transcriptome analysis. The 4,374,522-bp genome contains 3,954 protein-coding genes, 58 of which are present in two copies as a result of two independent tandem duplications, DU1 and DU2. DU1 is restricted to BCG Pasteur, although four forms of DU2 exist; DU2-I is confined to early BCG vaccines, like BCG Japan, whereas DU2-III and DU2-IV occur in the late vaccines. The glycerol-3-phosphate dehydrogenase gene, glpD2, is one of only three genes common to all four DU2 variants, implying that BCG requires higher levels of this enzyme to grow on glycerol. Further amplification of the DU2 region is ongoing, even within vaccine preparations used to immunize humans. An evolutionary scheme for BCG vaccines was established by analyzing DU2 and other markers. Lesions in genes encoding sigma-factors and pleiotropic transcriptional regulators, like PhoR and Crp, were also uncovered in various BCG strains; together with gene amplification, these affect gene expression levels, immunogenicity, and, possibly, protection against tuberculosis. Furthermore, the combined findings suggest that early BCG vaccines may even be superior to the later ones that are more widely used.

Is interleukin-4delta3 splice variant expression in bovine tuberculosis a marker of protective immunity?

Splice variants of the interleukin-4 (IL-4) cytokine gene have been described for humans, mice, and cattle. IL-4 splice variants have been shown to inhibit IL-4-mediated cellular responses and thus act as IL-4 antagonists. Recent work has highlighted the possibility of a correlation between IL-4 splice variants and protection against clinical tuberculosis. In this study we investigated the potential role of IL-4 splice variants IL-4delta2 and IL-4delta3 in cattle with bovine tuberculosis, using quantitative real-time reverse transcription-PCR. For this analysis we used naturally exposed tuberculin skin test-positive field reactor cattle, uninfected control cattle, and cattle from two experimental models of protective immunity against Mycobacterium bovis: (i) vaccination with M. bovis BCG and challenge with virulent M. bovis and (ii) infection with M. bovis and treatment with isoniazid (INH) prior to rechallenge. The cytokine levels of field reactor cattle were compared to the levels of uninfected controls, while in kinetic studies of BCG vaccination and INH treatment we compared pre-experimental values with sequential samples for each individual animal. The data revealed a significant increase in IL-4delta3 mRNA expression in field reactor cattle, which had no visible pathology compared to cattle with gross pathology typical of bovine tuberculosis. Increased IL-4delta3 expression in both cattle models of protective immunity (BCG vaccination and INH treatment) was transient over time, reaching significance in the INH treatment model. Our results support the hypothesis that IL-4delta3 is involved in protective immunity against M. bovis infection in cattle and are in accordance with clinical studies that have suggested a role for IL-4 splice variants in protective immunity in tuberculosis.

Metabolic fingerprints of Mycobacterium bovis cluster with molecular type: implications for genotype-phenotype links

Mycobacterium bovis is the causative agent of bovine tuberculosis. Various genetic typing techniques have been used to trace the reservoirs of infection; however, they have limited success in population genetics and outbreak studies. Fourier-transform infrared spectroscopy (FT-IR) is a rapid phenotypic typing technique, which may be used to generate a metabolic fingerprinting and is increasingly used to characterize bacteria. When coupled with multivariate cluster analysis, this powerful combination has sufficient resolving power to discriminate bacteria down to subspecies level; however, to date this method has not been used in the differentiation of mycobacteria. Multiple isolates of the ten major spoligotypes in the UK, recovered from different geographical locations, were analysed using FT-IR. Hierarchical cluster analysis of the spectra showed that the isolates could be differentiated according to their spoligotypes. Six of the spoligotype FT-IR clusters were very homogeneous and all isolates were recovered together. However, the remaining four groups displayed a more heterogeneous phenotype, which may reflect greater variation than previously suspected within these groups. Included in the ten spoligotypes are the two most dominant isolates in the UK, designated types 9 and 17. Whilst type 17 showed a highly conserved phenotype as judged by FT-IR, type 9 showed a very heterogeneous metabolic profile and isolates were recovered throughout the dendrogram. This variation in type 9 is reflected in the high degree of diversity observed by variable number tandem repeats (VNTR) analysis, underlining the exquisite resolving power of FT-IR.

Culling and cattle controls influence tuberculosis risk for badgers

Human and livestock diseases can be difficult to control where infection persists in wildlife populations. In Britain, European badgers (Meles meles) are implicated in transmitting Mycobacterium bovis, the causative agent of bovine tuberculosis (TB), to cattle. Badger culling has therefore been a component of British TB control policy for many years. However, large-scale field trials have recently shown that badger culling has the capacity to cause both increases and decreases in cattle TB incidence. Here, we show that repeated badger culling in the same area is associated with increasing prevalence of M. bovis infection in badgers, especially where landscape features allow badgers from neighboring land to recolonize culled areas. This impact on prevalence in badgers might reduce the beneficial effects of culling on cattle TB incidence, and could contribute to the detrimental effects that have been observed. Additionally, we show that suspension of cattle TB controls during a nationwide epidemic of foot and mouth disease, which substantially delayed removal of TB-affected cattle, was associated with a widespread increase in the prevalence of M. bovis infection in badgers. This pattern suggests that infection may be transmitted from cattle to badgers, as well as vice versa. Clearly, disease control measures aimed at either host species may have unintended consequences for transmission, both within and between species. Our findings highlight the need for policymakers to consider multiple transmission routes when managing multihost pathogens.

Bottlenecks and broomsticks: the molecular evolution of Mycobacterium bovis

Mycobacterium bovis is the cause of tuberculosis in cattle and is a member of the Mycobacterium tuberculosis complex. In contrast to many other pathogenic bacterial species, there is little evidence for the transfer and recombination of genes between cells. The clonality of this group of organisms indicates that the population structure is dominated by reductions in diversity, caused either by population bottlenecks or selective sweeps as entire chromosomes become fixed in the population. We describe how these forces have shaped not only the phylogeny of this group but also, at a very local level, the population structure of Mycobacterium bovis in the British Isles. We also discuss the practical implications of applying this knowledge to understanding the spread of infection and the development of improved vaccines and diagnostic tests.

Field evaluation of a novel differential diagnostic reagent for detection of Mycobacterium bovis in cattle

In the search for improved tools with which to control bovine tuberculosis, the development of enhanced immunodiagnostic reagents is a high priority. Such reagents are required to improve the performance of tuberculin-based reagents and allow the discrimination of vaccinated cattle from those infected with Mycobacterium bovis. In this study, we identified the immunodominant, frequently recognized peptides from Rv3873, Rv3879c, Rv0288, and Rv3019c, which, together with peptides comprising the current lead diagnostic antigens, ESAT-6 and CFP-10, were formulated into a peptide cocktail. In a test of naturally infected cattle, this cocktail was significantly better than tuberculin was for identifying skin test-negative animals with confirmed bovine tuberculosis. In addition, the specificity of this cocktail was not compromised by Mycobacterium bovis BCG vaccination. In summary, our results prioritize this peptide-based, fully synthetic reagent for assessment in larger trials.

Immunogenicity of Mycobacterium tuberculosis antigens in Mycobacterium bovis BCG-vaccinated and M. bovis-infected cattle

The development of novel vaccine strategies supplementing Mycobacterium bovis BCG (BCG) constitutes an urgent research challenge. To identify potential subunit vaccine candidates, we have tested a series of eight recently identified Mycobacterium tuberculosis antigens in M. bovis-infected and BCG-vaccinated cattle. These antigens were characterized on the basis of their ability to induce in vitro gamma interferon responses in infected or BCG-vaccinated calves. We were able to establish a hierarchy of these antigens based on how frequently they were recognized in both groups of animals. In particular, we were able to prioritize frequently recognized proteins like Rv0287, Rv1174, and Rv1196 for future evaluation as subunit vaccines to be used in BCG-protein heterologous prime-boost vaccination scenarios. In addition, the antigen most dominantly recognized in M. bovis-infected cattle in this study, Rv3616c, was significantly less frequently recognized by BCG vaccinees and could be a target to improve BCG, for example, by increasing its secretion, in a recombinant BCG vaccine.

Early antibody responses to experimental Mycobacterium bovis infection of cattle

Bovine tuberculosis persists as a costly zoonotic disease in numerous countries despite extensive eradication and control efforts. Sequential serum samples obtained from Mycobacterium bovis-infected cattle were evaluated for seroreactivity to mycobacterial antigens. Animals received M. bovis by aerosol, intratonsil, intranasal, or intratracheal inoculation. Assays included the multiantigen print immunoassay for determination of antigen recognition patterns, immunoblot analysis for sensitive kinetic studies, and the VetTB STAT-PAK test, a novel, rapid test based on lateral-flow technology. Responses to MPB83 were detected for all M. bovis-infected animals regardless of the route or strain of M. bovis used for inoculation. Other less commonly recognized antigens included ESAT-6, CFP-10, and MPB70. Responses to MPB83 were detectable as early as 4 weeks after inoculation, were boosted upon injection of purified protein derivatives for skin testing, and persisted throughout the course of each of the four challenge studies. MPB83-specific immunoglobulin M (IgM) was detected prior to MPB83-specific IgG detection; however, early IgM responses rapidly waned, suggesting a benefit of tests that detect both IgM- and IgG-specific antibodies. The VetTB STAT-PAK test detected responses in sera from 60% (15/25) of the animals by 7 weeks after challenge and detected responses in 96% (24/25) of the animals by 18 weeks. These findings demonstrate the potential for new-generation antibody-based tests for the early detection of M. bovis infection in cattle.

The safety and immunogenicity of Bacillus Calmette-Guérin (BCG) vaccine in European badgers (Meles meles)

European badgers (Meles meles) are a wildlife reservoir for Mycobacterium bovis (M. bovis) in Great Britain (GB) and the Republic of Ireland and therefore constitute a potential source of infection for cattle. Reduction of badger densities in the Republic of Ireland has resulted in an associated reduction in the risk of a herd break-down with bovine tuberculosis and a study to determine whether this is also the case in GB has been running since 1997. If badgers are a significant source of M. bovis infection for cattle, vaccinating badgers with Bacillus Calmette-Guérin (BCG) might prove to be a long term, cost-effective strategy for controlling bovine tuberculosis whilst preserving badger populations. As a first step towards BCG vaccination of wild badgers, it was necessary to demonstrate safety of the vaccine in captive badgers. Therefore, captive badgers were vaccinated with a commercial source of BCG that is already licensed for administration to humans in GB-BCG Danish SSI. Using a protocol prescribed by the Veterinary Medicines Directorate (VMD) of GB, badgers were vaccinated with two consecutive doses of BCG via either the subcutaneous (s.c.) or intra-muscular (i.m.) routes. The first dose was high, ranging from 16 to 22 x 10(7) colony-forming units (CFU), and was followed 15 weeks later by a lower dose in the range of 4-7 x 10(5)CFU. Local reaction at the site of injection and general responses (body temperature, haematology and blood serum chemistry), behaviour and excretion of BCG were monitored for 28 weeks from the time of the first vaccination. The only side-effect observed was the occurrence of localised swelling at the site of BCG injection that disappeared 48 days after i.m. vaccination but persisted longer in the group vaccinated by the s.c. route. Immunological responses were measured at regular intervals. Strong cellular responses were observed 13 days after the first vaccination, which persisted for 76 days. The lower dose induced a weaker and shorter-lived response.

Development of cattle TB vaccines in the UK

In 1996, an independent scientific committee chaired by Professor John Krebs, tasked to review the problem of bovine tuberculosis (TB) in GB, concluded that vaccination of cattle offered the best long-term solution for controlling the disease in the National Herd. This view has been re-affirmed recently in the House of Commons Environment, Food and Rural Affairs Committee's report on Bovine TB (2004) and by the findings of the Independent Scientific Group Vaccine Scoping Sub-committee. Significant progress in developing TB vaccines for cattle has been made over the last 5 years. Specifically: (i) DNA or protein subunit vaccines used in combination with BCG have been shown to give superior protection against experimental challenge in cattle than BCG (heterologous prime-boost); (ii) prototype reagents that allow discrimination between vaccinated and infected animals have been developed; and (iii) and correlates of disease severity have been identified that can predict the success or failure of vaccination. These significant advances are detailed in this review with a summary of future directions that TB vaccine development for cattle is likely to take.

Molecular analysis of human and bovine tubercle bacilli from a local setting in Nigeria

To establish a molecular epidemiological baseline for the strains causing tuberculosis in Nigeria, a survey of isolates from humans and cattle was carried out. Spoligotyping and variable-number tandem-repeat analysis revealed that the majority of tuberculosis disease in humans in Ibadan, southwestern Nigeria, is caused by a single, closely related group of Mycobacterium tuberculosis strains. Using deletion typing, we show that approximately 13% of the disease in humans in this sample was caused by strains of Mycobacterium africanum and Mycobacterium bovis rather than M. tuberculosis. Molecular analysis of strains of M. bovis recovered from Nigerian cattle show that they form a group of closely related strains that show similarity to strains from neighboring Cameroon. Surprisingly, the strains of M. bovis recovered from humans do not match the molecular type of the cattle strains, and possible reasons for this are discussed. This is the first molecular analysis of M. tuberculosis complex strains circulating among humans and cattle in Nigeria, the results of which have significant implications for disease control.

Ante mortem diagnosis of tuberculosis in cattle: a review of the tuberculin tests, gamma-interferon assay and other ancillary diagnostic techniques

The early, preclinical stages of bovine TB can be detected in live animals by the use of tests of cellular immunity (the skin, gamma-interferon and lymphocyte transformation tests). Tests of humoral (antibody) immunity, Mycobacterium bovis PCR probes on early tissue cultures or live cattle specimens, and tests based on "electronic nose" technology have been developed more recently. The key measure of diagnostic test accuracy is the relationship between sensitivity and specificity, which determines the false-positive and false-negative proportions. None of the tests currently available for the diagnosis of bovine TB allow a perfectly accurate determination of the M. bovis infection status of cattle. Although various factors can reduce the sensitivity and specificity of the skin tests, these remain the primary ante mortem diagnostic tools for TB in cattle, providing a cost-effective and reliable means of screening entire cattle populations. Despite the inescapable limitations of existing diagnostic tests, bovine TB has been effectively eradicated from many developed countries and regions with the implementation of sound programmes of regular tuberculin skin testing and removal of reactors, coupled with slaughterhouse surveillance for undetected infections, repeat testing and culling of infected herds, cattle movement restrictions to prevent introduction of infected animals and occasional slaughter of entire herds with intractable breakdowns. This is likely to remain the mainstay of bovine TB control programmes for the foreseeable future. Additionally, newer ancillary in vitro diagnostic assays are now available to TB control programme managers to supplement the skin tests in defined circumstances according to the specific disease situation in each country or region. The strategic deployment of ancillary in vitro tests alongside the primary skin tests has enhanced the detection of M. bovis-infected cattle and reduced the number of animals slaughtered as false positives.

Progress in the development of vaccines and diagnostic reagents to control tuberculosis in cattle

The sharp rise of bovine tuberculosis (TB) in Great Britain and the continuing problem of wild life reservoirs in countries such as New Zealand and Great Britain have resulted in increased research efforts into the disease. Two of the goals of this research are to develop (1) cattle vaccines against TB and (2) associated diagnostic reagents that can differentiate between vaccinated and infected animals (differential diagnosis). This review summarises recent progress and describes efforts to increase the protective efficacy of the only potential TB vaccine currently available, Mycobacterium bovis BCG, and to develop specific reagents for differential diagnosis. Vaccination strategies based on DNA or protein subunit vaccination, vaccination with live viral vectors as well as heterologous prime-boost scenarios are discussed. In addition, we outline results from studies aimed at developing diagnostic reagents to allow the distinction of vaccinated from infected animals, for example antigens that are not expressed by vaccines like Mycobacterium bovis Bacille-Calmette-Guérin, but recognised strongly in Mycobacterium bovis infected cattle.

Immune responses induced in cattle by vaccination with a recombinant adenovirus expressing Mycobacterial antigen 85A and Mycobacterium bovis BCG

Cattle were vaccinated with an adenovirus expressing the mycobacterial antigen 85A (rAd85A), with Mycobacterium bovis BCG followed by rAd85A heterologous boosting, or with rAd85A followed by BCG boosting. BCG/rAd85A resulted in the highest direct gamma interferon responses. Cultured enzyme-linked immunospot assay analysis demonstrated that memory responses were induced by all three protocols but were strongest after BCG/rAd85A and rAd85A/BCG vaccination.

Histopathogenesis of experimental Mycobacterium bovis infection in mice

In-bred strains of mice are commonly used to model pathogenic infections due to their cost and utility. In order to understand better the nature of experimental tuberculosis in mice, we infected BALB/c mice with a virulent field isolate of Mycobacterium bovis. Mice were sacrificed at intervals in order to visualise the pathological lesions in major internal organs. Pathological lesions in tissues increased in number and severity over time and replicated many of the salient features observed in badgers and cattle infected with M. bovis. These similarities are discussed. Examination of pathological lesions at terminal stages of infection enabled us to suggest the lethal effects of M. bovis mediated through the host response. We conclude that the mouse is a relevant surrogate species in which to study the virulence of M. bovis, as well as the influence of vaccination on its pathogenicity.

Protective efficacy induced by Mycobacterium bovis bacille Calmette-Guèrin can be augmented in an antigen independent manner by use of non-coding plasmid DNA

Tuberculosis caused by infection with Mycobacterium tuberculosis or M. bovis remains one of the most important infectious diseases of man and animals, and continues to inflict a huge cost in both health and financial terms. The current vaccine, BCG demonstrates variable efficacy and so a more robust vaccine strategy to either replace or supplement BCG is required. We have utilised a DNA prime-BCG boost strategy in a murine M. bovis challenge model using a cocktail of 3 DNA vaccines (encoding Hsp65, Hsp70 and Apa) followed by BCG. Controls were inoculated with vector DNA only, coding DNA only, BCG only or vector DNA followed by BCG boost. Analysis of immune responses by ELISpot prior to challenge, revealed that the coding DNA/BCG prime boost resulted in an increased frequency of antigen-specific IFNgamma producing cells compared to the other regimes. When spleen cell cytokine production to BCG antigens was analysed, significantly more IFNgamma and IL-12 was seen in those groups primed with DNA (coding or vector) prior to BCG than those receiving BCG alone. Analysis of bacterial counts revealed that DNA priming followed by BCG boost further improved the protective immunity induced by BCG alone. Surprisingly, inoculation with vector DNA was as efficacious as the coding DNA in enhancing BCG protection. Taken together these results indicate that whilst the coding DNA vaccines induce antigen specific responses, treatment with the vector DNA is sufficient for the increase in protective immunity over that induced by BCG, suggesting that the vector DNA may be acting as a non-specific adjuvant for BCG immunization.

Recent advances in our knowledge of Mycobacterium bovis: a feeling for the organism

Significant and rapid progress has been made in our knowledge and understanding of Mycobacterium bovis since the last international M. bovis conference 5 years ago. Much of this progress has been underpinned by the completion of the genome sequence. This important milestone has catalysed research into the development of a number of improved tools with which to combat bovine tuberculosis. In this article we will review recent progress made in the development of these tools and in our understanding of the organism, its evolution and spread. Comparison of the genome sequence with those of other members of the Mycobacterium tuberculosis complex has enabled insights into the evolution of M. bovis. This analysis also indicates that the M. tuberculosis complex have the propensity to adapt to new host species. The use of high throughput molecular typing methods has revealed that the recent bovine tuberculosis epidemic in Great Britain is being driven by a number of clonal expansions, which cannot be explained by random mutation and drift alone. Completion of a number of mycobacterial genome sequences has allowed the development of antigen mining techniques that rapidly identify M. bovis-specific genes. These can then be used as reagents in the gamma interferon assay to increase the specificity of the assay and also to discriminate between Bacillus of Calmette and Guérin (BCG) vaccinated animals and those infected with M. bovis. In the longer term, comparisons between the genomes of M. bovis and BCG will allow insight into how BCG became attenuated following serial passage on artificial growth media and reveal clues into how to improve the vaccine efficacy of BCG.

Shedding of Mycobacterium bovis in the nasal mucus of cattle infected experimentally with tuberculosis by the intranasal and intratracheal routes

Four groups of six calves were infected experimentally with either a low dose of approximately 10(4) colony-forming units (cfu) or a high dose of approximately 10(6) cfu of Mycobacterium bovis. Each dose was delivered by the intranasal and intratracheal routes. More severe disease was observed in the groups inoculated with the high dose. Visible lesions were identified in 21 of the 24 animals, all of which also gave positive skin tests and interferon-gamma (IFN-gamma) responses. Nasal shedding was detected in 15 of the 24 animals and the frequency of shedding was influenced by both the route and the dose of infection; no shedding was observed in the group infected intratracheally with the low dose. Two of the 15 confirmed shedders had no visible lesions at postmortem examination; both of these calves gave IFN-gamma responses but only one was skin test positive.

Minimum infective dose of Mycobacterium bovis in cattle

The aim of this work was to determine the minimum infective dose of Mycobacterium bovis necessary to stimulate specific immune responses and generate pathology in cattle. Four groups of calves (20 animals) were infected by the intratracheal route with 1,000, 100, 10, or 1 CFU of M. bovis. Specific immune responses (gamma interferon [IFN-gamma] and interleukin-4 [IL-4] responses) to mycobacterial antigens were monitored throughout the study, and the responses to the tuberculin skin test were assessed at two times. Rigorous post mortem examinations were performed to determine the presence of pathology, and samples were taken for microbiological and histopathological confirmation of M. bovis infection. One-half of the animals infected with 1 CFU of M. bovis developed pulmonary pathology typical of bovine tuberculosis. No differences in the severity of pathology were observed for the different M. bovis doses. All animals that developed pathology were skin test positive and produced specific IFN-gamma and IL-4 responses. No differences in the sizes of the skin test reactions, the times taken to achieve a positive IFN-gamma result, or the levels of the IFN-gamma and IL-4 responses were observed for the different M. bovis doses, suggesting that diagnostic assays (tuberculin skin test and IFN-gamma test) can detect cattle soon after M. bovis infection regardless of the dose. This information should be useful in modeling the dynamics of bovine tuberculosis in cattle and in assessing the risk of transmission.