Progress in the development of tuberculosis vaccines for cattle and wildlife

Vaccine Preventable Zoonotic Diseases: Challenges and Opportunities for Public Health Progress

Zoonotic diseases represent a heavy global burden, causing important economic losses, impacting animal health and production, and costing millions of human lives. The vaccination of animals and humans to prevent inter-species zoonotic disease transmission is an important intervention. However, efforts to develop and implement vaccine interventions to reduce zoonotic disease impacts are often limited to the veterinary and agricultural sectors and do not reflect the shared burden of disease. Multisectoral collaboration, including co-development opportunities for human and animal vaccines, expanding vaccine use to include animal reservoirs such as wildlife, and strategically using vaccines to interrupt complex transmission cycles is needed. Addressing zoonoses requires a multi-faceted One Health approach, wherein vaccinating people and animals plays a critical role.

Diagnosis of tuberculosis in wildlife: a systematic review

Animal tuberculosis (TB) is a multi-host disease caused by members of the Mycobacterium tuberculosis complex (MTC). Due to its impact on economy, sanitary standards of milk and meat industry, public health and conservation, TB control is an actively ongoing research subject. Several wildlife species are involved in the maintenance and transmission of TB, so that new approaches to wildlife TB diagnosis have gained relevance in recent years. Diagnosis is a paramount step for screening, epidemiological investigation, as well as for ensuring the success of control strategies such as vaccination trials. This is the first review that systematically addresses data available for the diagnosis of TB in wildlife following the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The article also gives an overview of the factors related to host, environment, sampling, and diagnostic techniques which can affect test performance. After three screenings, 124 articles were considered for systematic review. Literature indicates that post-mortem examination and culture are useful methods for disease surveillance, but immunological diagnostic tests based on cellular and humoral immune response detection are gaining importance in wildlife TB diagnosis. Among them, serological tests are especially useful in wildlife because they are relatively inexpensive and easy to perform, facilitate large-scale surveillance and can be used both ante- and post-mortem. Currently available studies assessed test performance mostly in cervids, European badgers, wild suids and wild bovids. Research to improve diagnostic tests for wildlife TB diagnosis is still needed in order to reach accurate, rapid and cost-effective diagnostic techniques adequate to a broad range of target species and consistent over space and time to allow proper disease monitoring.

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.

Challenges for controlling bovine tuberculosis in South Africa

All effects taken together, bovine tuberculosis (bTB) has a long-term detrimental effect on bovine herds and many wildlife species in South Africa. The disease is not only found in domestic cattle but also in African buffaloes and has to date been diagnosed in 21 wildlife species, including several rare and endangered species, thus having a potentially serious effect on conservation and biodiversity. In cattle, bTB is mostly characterised by sporadic outbreaks, but bovine herds chronically infected with the clinical disease are not uncommon. Presently, the recognised bTB control strategy in South Africa is based on 'test and slaughter', using the intradermal tuberculin test, followed by the slaughter of animals that have tested positive. Affected herds are placed under veterinary quarantine with movement restrictions until the outbreak is eradicated; this can take several years or last indefinitely if the outbreak cannot be eradicated. The same measures apply to infected buffalo populations, often with no prospect of ever being eradicated. This strategy is neither practical nor viable in the context of a communal farming system and becomes unethical when dealing with valuable wildlife reservoir hosts. Transmission of bTB between wildlife and cattle has been demonstrated and emphasises the need for an effective, affordable and culturally acceptable control strategy to curb the spread of bTB in South Africa. In countries with similar challenges, vaccination has been used and found to be promising for treating wild and domestic reservoir species and may hence be of value as a complementary tool for bTB control in South Africa.

Persistent Spillback of Bovine Tuberculosis From White-Tailed Deer to Cattle in Michigan, USA: Status, Strategies, and Needs

Free-ranging white-tailed deer (Odocoileus virginianus) are believed to be a self-sustaining reservoir for bovine tuberculosis (bTB) in northeastern Lower Michigan, USA. Although a comprehensive control program is in place and on-farm mitigation strategies to curtail bTB transmission between cattle and deer have been implemented for over a decade, cattle and deer continue to become infected with the disease. Thus, renewed motivation to eradicate bTB is needed if that is truly the goal. Recurrent detection of bTB in cattle in the region is of mounting concern for state and federal agricultural agencies, producers, and wildlife managers. Current on-farm mitigation efforts include fencing and refined cattle feeding and watering practices. Liberal removal of antlerless deer through hunter harvest and disease control permits (DCPs) issued to cattle producers and agency sharp shooters have also been ongoing. Although these strategies have merit and efforts to reduce prevalence in deer and occurrence of positive farms are elevated, additional actions are needed. Heightened management actions to combat bTB in deer could include deer vaccination programs, strategic habitat manipulations to redistribute deer from farms, and precision removal of deer in proximity to high-risk farms. Foundational research to address development and delivery of vaccine to free-ranging deer is complete. Strategic management and habitat manipulation could reduce and disperse local concentrations of deer while better meeting wildlife, forestry, and agricultural goals. The responses of local deer populations to targeted removal of individuals are generally understood and there is potential to reduce deer activity around agricultural operations while allowing them to persist nearby on natural foods. We summarize the history and progress to date, discuss the realized merit of novel management strategies, and suggest options to rid deer and cattle in Michigan of bTB.

Comparative proteomics identified immune response proteins involved in response to vaccination with heat-inactivated Mycobacterium bovis and mycobacterial challenge in cattle

There is an imperative need for effective control of bovine tuberculosis (BTB) on a global scale and vaccination of cattle may prove to be pivotal in achieving this. The oral and parenteral use of a heat-inactivated Mycobacterium bovis (M. bovis) vaccine has previously been found to confer partial protection against BTB in several species. A role for complement factor C3 has been suggested in wild boar, but the exact mechanism by which this vaccine provides protection remains unclear. In the present study, a quantitative proteomics approach was used to analyze the white blood cell proteome of vaccinated cattle in comparison to unvaccinated controls, prior (T0) and in response to vaccination, skin test and challenge (T9 and T12). The Fisher's exact test was used to compare the proportion of positive reactors to standard immunological assays for BTB (the BOVIGAM^® assay, IDEXX TB ELISA and skin test) between the vaccinated and control groups. Using reverse-phase liquid-chromatography tandem mass spectrometry (RP-LC-MS/MS), a total of 12,346 proteins were identified with at least two peptides per protein and the Chi²-test (P = 0.05) determined 1,222 to be differentially represented at the key time point comparisons. Gene ontology (GO) analysis was performed in order to determine the biological processes (BPs), molecular functions (MFs) and cell components (CCs) the proteins formed part of. The analysis was focused on immune system BPs, specifically. GO analysis revealed that the most overrepresented proteins in immune system BPs, were kinase activity and receptor activity molecular functions and extracellular, Golgi apparatus and endosome cell components and included complement factor C8α and C8β as well as toll-like receptors 4 (TLR4) and 9 (TLR9). Proteins of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) (JAK-STAT) and protein kinase C (PKC) signaling pathways were furthermore found to potentially be involved in the immune response elicited by the inactivated vaccine. In conclusion, this study provides a first indication of the role of several immune system pathways in response to the heat-inactivated M. bovis vaccine and mycobacterial challenge.

Use of the Human Vaccine, Mycobacterium bovis Bacillus Calmette Guérin in Deer

The only vaccine ever approved for human tuberculosis was developed a century ago from an isolate of Mycobacterium bovis derived from a tuberculous cow. Initial safety and efficacy studies of an attenuated version of this isolate were conducted in cattle and other animals. In 1921 the first human, an infant, was orally dosed with this attenuated strain that came to be known as M. bovis bacillus Calmette-Guérin (BCG); named for Albert Calmette and Camille Guérin, the two French scientists that developed the strain. Since 1921, billions of people have been vaccinated with BCG making it the oldest, most widely used, and safest vaccine in use today. It is also the tuberculosis vaccine most studied for use in wildlife, including deer. While BCG vaccination of deer may not reliably prevent infection, it consistently decreases lesion severity, minimizing large, necrotic lesions, which often contain large numbers of bacilli. It is believed that decreased lesion severity correlates with decreased disease transmission; however, this hypothesis remains to be proven. Safety studies in white-tailed deer show BCG may persist in lymphoid tissues for up to 12 months; a factor to be considered in deer used for food. Beyond efficacy and safety, methods of vaccine delivery to free-ranging deer are also under investigation, both in the laboratory and in the field. The ideal delivery method is effective, efficient and safe for non-target species, including livestock. Ingestion of BCG by cattle is of special concern as such cattle may present as "false positives" using currently approved diagnostic methods, thus interfering with efforts by animal health agencies to monitor cattle for tuberculosis. An effective BCG vaccine for deer would be of value in regions where free-ranging deer represent a potential source of M. bovis for livestock. Such a vaccine would also be beneficial to farmed deer where M. bovis represents a serious threat to trade and productivity.

Immune response profiles of calves following vaccination with live BCG and inactivated Mycobacterium bovis vaccine candidates

Conventional control and eradication strategies for bovine tuberculosis (BTB) face tremendous difficulties in developing countries; countries with wildlife reservoirs, a complex wildlife-livestock-human interface or a lack of veterinary and veterinary public health surveillance. Vaccination of cattle and other species might in some cases provide the only suitable control strategy for BTB, while in others it may supplement existing test-and-slaughter schemes. However, the use of live BCG has several limitations and the global rise of HIV/AIDS infections has furthermore warranted the exploration of inactivated vaccine preparations. The aim of this study was to compare the immune response profiles in response to parenteral vaccination with live BCG and two inactivated vaccine candidates in cattle.

Twenty-four mixed breed calves (Bos taurus) aged 4–6 months, were allocated to one of four groups and vaccinated sub-cutaneously with live M. bovis BCG (Danish 1331), formalin-inactivated M. bovis BCG, heat-killed M. bovis or PBS/Montanide™ (control). Interferon-γ responsiveness and antibody production were measured prior to vaccination and at weekly intervals thereafter for twelve weeks. At nine weeks post-priming, animals were skin tested using tuberculins and MTBC specific protein cocktails and subsequently challenged through intranodular injection of live M. bovis BCG.

The animals in the heat-killed M. bovis group demonstrated strong and sustained cell-mediated and humoral immune responses, significantly higher than the control group in response to vaccination, which may indicate a protective immune profile. Animals in this group showed reactivity to the skin test reagents, confirming good vaccine take. Lastly, although not statistically significant, recovery of BCG after challenge was lowest in the heat-killed M. bovis group.

In conclusion, the parenteral heat-killed M. bovis vaccine proved to be clearly immunogenic in cattle in the present study, urging further evaluation of the vaccine in challenge studies using virulent M. bovis and assessment of vaccine efficacy in field conditions.

Efficacies of prevention and control measures applied during an outbreak in Southwest Madrid, Spain

Leishmaniasis is a vector-borne disease of worldwide distribution, currently present in 98 countries. Since late 2010, an unusual increase of human visceral and cutaneous leishmaniasis cases has been observed in the south-western Madrid region, totaling more than 600 cases until 2015. Some hosts, such as human, domestic dog and cat, rabbit (Oryctolagus cuniculus), and hare (Lepus granatensis), were found infected by the parasite of this disease in the area. Hares were described as the most important reservoir due to their higher prevalence, capacity to infect the vector, and presence of the same strains as in humans. Various measures were adopted to prevent and control the disease, and since 2013 there was a slight decline in the human sickness. We used a mathematical model to evaluate the efficacy of each measure in reducing the number of infected hosts. We identified in the present model that culling both hares and rabbits, without immediate reposition of the animals, was the best measure adopted, decreasing the proportion of all infected hosts. Particularly, culling hares was more efficacious than culling rabbits to reduce the proportion of infected individuals of all hosts. Likewise, lowering vector contact with hares highly influenced the reduction of the proportion of infected hosts. The reduction of the vector density per host in the park decreased the leishmaniasis incidence of hosts in the park and the urban areas. On the other hand, the reduction of the vector density per host of the urban area (humans, dogs and cats) decreased only their affected population, albeit at a higher proportion. The use of insecticide-impregnated collar and vaccination in dogs affected only the infected dogs' population. The parameters related to the vector contact with dog, cat or human do not present a high impact on the other hosts infected by Leishmania. In conclusion, the efficacy of each control strategy was determined, in order to direct future actions in this and in other similar outbreaks. The present mathematical model was able to reproduce the leishmaniasis dynamics in the Madrid outbreak, providing theoretical support based on successful experiences, such as the reduction of human cases in Southwest Madrid, Spain.

Differential Cell Composition and Cytokine Expression Within Lymph Node Granulomas from BCG-Vaccinated and Non-vaccinated Cattle Experimentally Infected with Mycobacterium bovis

Cattle vaccination against bovine tuberculosis (bTB) has been proposed as a supplementary method to help control the incidences of this disease. Bacillus Calmette-Guérin (BCG) is currently the only viable candidate vaccine for immunization of cattle against bTB, caused by Mycobacterium bovis (M. bovis). In an attempt to characterize the differences in the immune response following M. bovis infection between BCG-vaccinated and non-vaccinated animals, a combination of gross pathology, histopathology and immunohistochemical (IHC) analyses was used. BCG vaccination was found to significantly reduce the number of gross and microscopic lesions present within the lungs and lymph nodes. Additionally, the microscopically visible bacterial load of stages III and IV granulomas was reduced. IHC using cell surface markers revealed the number of CD68+ (macrophages), CD3+ (T lymphocytes) and WC1+ cells (γδ T cells) to be significantly reduced in lymph node granulomas of BCG-vaccinated animals, when compared to non-vaccinated animals. B lymphocytes (CD79a+) were significantly increased in BCG-vaccinated cattle for granulomas at stages II, III and IV. IHC staining for iNOS showed a higher expression in granulomas from BCG-vaccinated animals compared to non-vaccinated animals for all stages, being statistically significant in stages I and IV. TGFβ expression decreased alongside the granuloma development in non-vaccinated animals, whereas BCG-vaccinated animals showed a slight increase alongside lesion progression. IHC analysis of the cytokines IFN-γ and TNF-α demonstrated significantly increased expression within the lymph node granulomas of BCG-vaccinated cattle. This is suggestive of a protective role for IFN-γ and TNF-α in response to M. bovis infection. Findings shown in this study suggest that the use of BCG vaccine can reduce the number and severity of lesions, induce a different phenotypic response and increase the local expression of key cytokines related to protection.

Middle East respiratory syndrome: obstacles and prospects for vaccine development

The recent emergence of Middle East respiratory syndrome (MERS) highlights the need to engineer new methods for expediting vaccine development against emerging diseases. However, several obstacles prevent pursuit of a licensable MERS vaccine. First, the lack of a suitable animal model for MERS complicates the in vivo testing of candidate vaccines. Second, due to the low number of MERS cases, pharmaceutical companies have little incentive to pursue MERS vaccine production as the costs of clinical trials are high. In addition, the timeline from bench research to approved vaccine use is 10 years or longer. Using novel methods and cost-saving strategies, genetically engineered vaccines can be produced quickly and cost-effectively. Along with progress in MERS animal model development, these obstacles can be circumvented or at least mitigated.

Toward eradication: the effect of Mycobacterium bovis infection in wildlife on the evolution and future direction of bovine tuberculosis management in New Zealand

New Zealand's bovine tuberculosis (TB) control programme has greatly reduced the burden of tuberculosis on the farming industry, from 11% of mature cattle found with TB at slaughter in 1905 to <0.003% in 2012/13. New Zealand implemented TB control measures in cattle from the mid-twentieth century, and later in farmed deer. Control was based on established methods of tuberculin testing of herds, slaughter of suspect cases, and livestock movement control. Unexplained regional control failures and serious disease outbreaks were eventually linked to wildlife-vectored infection from the introduced Australian brushtail possum (Trichosurus vulpecula), which also triggered a wildlife disease complex involving a range of introduced species. This paper reviews the progressive elucidation of the epidemiology of Mycobacterium bovis in New Zealand's wildlife and farmed livestock, and the parallel development of research-led, multi-faceted TB control strategies required to protect New Zealand's livestock industries from damaging infection levels. The adoption of coordinated national pest management strategies, with increasingly ambitious objectives agreed between government and industry funders, has driven a costly but very successful management regime targeted at controlling TB in the possum maintenance host. This success has led to initiation of a strategy designed to eradicate TB from New Zealand's livestock and wildlife, which is considered a realistic long-term prospect.

Efficacy of a vaccine formula against tuberculosis in cattle

"Test-and-slaughter" has been successful in industrialized countries to control and eradicate tuberculosis from cattle; however, this strategy is too expensive for developing nations, where the prevalence is especially high. Vaccination with the Calmette-Guérin (BCG) strain has been shown to protect against the development of lesions in vaccinated animals: mouse, cattle and wildlife species. In this study, the immune response and the pathology of vaccinated (BCG-prime and BCG prime-CFP-boosted) and unvaccinated (controls) calves were evaluated under experimental settings. A 10(6) CFU dose of the BCG strain was inoculated subcutaneously on the neck to two groups of ten animas each. Thirty days after vaccination, one of the vaccinated groups was boosted with an M. bovis culture filtrate protein (CFP). Three months after vaccination, the three groups of animals were challenged with 5×10(5) CFU via intranasal by aerosol with a field strain of M. bovis. The immune response was monitored throughout the study. Protection was assessed based on immune response (IFN-g release) prechallenge, presence of visible lesions in lymph nodes and lungs at slaughter, and presence of bacilli in lymph nodes and lung samples in histological analysis. Vaccinated cattle, either with the BCG alone or with BCG and boosted with CFP showed higher IFN-g response, fewer lesions, and fewer bacilli per lesion than unvaccinated controls after challenge. Animals with low levels of IFN-g postvaccine-prechallenge showed more lesions than animals with high levels. Results from this study support the argument that vaccination could be incorporated into control programs to reduce the incidence of TB in cattle in countries with high prevalence.

Attenuated Listeria monocytogenes, a Mycobacterium tuberculosis ESAT-6 antigen expression and delivery vector for inducing an immune response

We selectively expressed protective Mycobacterium tuberculosis antigen ESAT-6 in recombinant strains Lm(esat-6) and LmΔactA/plcB(esat-6) to evaluate the capacity of Listeria monocytogenes to deliver antigens from M. tuberculosis, and we studied the pathogenicity and immunogenicity of these strains compared with virulent parental strain yzuLm4 and attenuated strain LmΔactA/plcB. The two recombinant strains retained listeriolysin O hemolytic activity, escaped into the cytosol niche and established replication in the macrophage-like RAW264.7 cell line; however, these strains showed decreased virulence in C57BL/6 mice. Histopathology revealed no obvious pathological changes following administration of the recombinant strains to mice, indicating that they were significantly safer than parental strains. Moreover, intravenous vaccination of mice with the recombinant strains elicited specific Th1-type cellular immunity, splenocyte proliferation and effective CTL activity in vivo. Thus, attenuated L. monocytogenes strains can be used as effective vectors for delivering M. tuberculosis ESAT-6 and inducing a cellular immune response, suggesting that such vectors may be effective as novel vaccines for preventing tuberculosis.

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.

Live-trapping and bovine tuberculosis testing of free-ranging white-tailed deer for targeted removal

Context Significant efforts have been made in Michigan, USA, to reduce the prevalence of bovine tuberculosis (TB) in free-ranging white-tailed deer (Odocoileus virginianus) over the past 15 years. Since 2002, however, prevalence has changed little, prompting the need for new control strategies. Aims In January–March of 2007 and 2008, a trap–test–cull project was conducted on an 11 000-ha property in the north-eastern Lower Peninsula of Michigan. The objectives were to assess the feasibility of live-trapping and testing white-tailed deer for TB as a means for targeted removal and estimate the cost of this effort. Methods Live-trapped deer were ear-tagged and a blood sample was drawn for use with the CervidTB STAT-PAK (commonly called Rapid Test) for TB diagnosis in the field. Deer testing negative were released, whereas deer testing positive were euthanised to confirm blood-test results via bacterial culture. Key results In all, 762 (741 with known sex and age) individual deer were captured and tested for TB. Adults comprised 59% (437 of 741) of the captures. Eight (1.8%) adults were positive on the blood test; six of eight (1.4% of adults) were confirmed TB positive via bacterial culture. Estimated TB prevalence in the present study was 2.5% (adjusted for Rapid Test sensitivity of 56%), being lower than what would be expected on the basis of routine hunter-harvest surveillance for this site which has yielded prevalence rates from 3.4% to 4.8%. Results demonstrated the ability to trap and test a substantial number of deer given high deer densities (16–20 deer per km2), availability of traps and abundant workers. The 2-year project cost a total of ~US$228 000, or US$38 000 per culture-positive animal. Conclusions Because of the cost and effort involved, a project such as the present one applied to Michigan’s larger TB-management area (148 018 ha) is not feasible. Implications If the efficiency and effectiveness of a trap–test–cull project could be improved by vaccinating test-negative animals, should a vaccine be approved for use in free-ranging white-tailed deer, a trap–test–cull project applied on a scale similar to the present study may prove beneficial by possibly reducing disease transmission, in addition to removing TB-positive animals.

Experimental model of tuberculosis in the domestic goat after endobronchial infection with Mycobacterium caprae

Caprine tuberculosis (TB) has increased in recent years, highlighting the need to address the problem the infection poses in goats. Moreover, goats may represent a cheaper alternative for testing of prototype vaccines in large ruminants and humans. With this aim, a Mycobacterium caprae infection model has been developed in goats. Eleven 6-month-old goats were infected by the endobronchial route with 1.5 × 10(3) CFU, and two other goats were kept as noninfected controls. The animals were monitored for clinical and immunological parameters throughout the experiment. After 14 weeks, the goats were euthanized, and detailed postmortem analysis of lung lesions was performed by multidetector computed tomography (MDCT) and direct observation. The respiratory lymph nodes were also evaluated and cultured for bacteriological analysis. All infected animals were positive in a single intradermal comparative cervical tuberculin (SICCT) test at 12 weeks postinfection (p.i.). Gamma interferon (IFN-γ) antigen-specific responses were detected from 4 weeks p.i. until the end of the experiment. The humoral response to MPB83 was especially strong at 14 weeks p.i. (13 days after SICCT boost). All infected animals presented severe TB lesions in the lungs and associated lymph nodes. M. caprae was recovered from pulmonary lymph nodes in all inoculated goats. MDCT allowed a precise quantitative measure of TB lesions. Lesions in goats induced by M. caprae appeared to be more severe than those induced in cattle by M. bovis over a similar period of time. The present work proposes a reliable new experimental animal model for a better understanding of caprine tuberculosis and future development of vaccine trials in this and other species.

The role of wildlife in transboundary animal diseases

This paper identifies some of the more important diseases at the wildlife-livestock interface and the role wildlife plays in disease transmission. Domestic livestock, wildlife and humans share many similar pathogens. Pathogens of wild or domestic animal origin that can cause infections in humans are known as zoonotic organisms and the converse are termed as anthroponotic organisms. Seventy-seven percent of livestock pathogens and 91% of domestic carnivore pathogens are known to infect multiple hosts, including wildlife. Understanding this group of pathogens is critical to public health safety, because they infect a wide range of hosts and are most likely to emerge as novel causes of infection in humans and domestic animals. Diseases at the wildlife-livestock interface, particularly those that are zoonotic, must be an area of focus for public health programs and surveillance for emerging infectious diseases. Additionally, understanding wildlife and their role is a vital part of understanding the epidemiology and ecology of diseases. To do this, a multi-faceted approach combining capacity building and training, wildlife disease surveillance, wildlife-livestock interface and disease ecology studies, data and information sharing and outbreak investigation are needed.

Mycobacterium bovis antigens for the differential diagnosis of vaccinated and infected cattle

The urgency for new and improved cattle vaccines and diagnostic reagents for Bovine tuberculosis (TB) has made their development a research priority in Great Britain (GB). Significant progress has been made to develop specific antigens that allow the differentiation of BCG vaccinated and Mycobacterium bovis infected cattle (DIVA test). This has been greatly facilitated by the completion of the genome sequences of M. tuberculosis, M. bovis and BCG Pasteur and the subsequent application of comparative genome and transcriptome analysis to define DIVA antigens that complemented the prototype DIVA antigens ESAT-6 and CFP-10 by increasing their test sensitivity. Finally, we present an up-date of our current approaches in this area.

Host expression of methylmalonyl-CoA mutase and tuberculosis: a missing link?

Bovine tuberculosis (bTB) is a disease caused by Mycobacterium bovis and closely related species of the Mycobacterium tuberculosis complex. bTB is an important health problem affecting livestock, wild animals and accounting for up to 10% of human TB cases worldwide. Several hypotheses have been considered to explain the low incidence of active TB despite high infection rates and the variable response to BCG vaccination. These hypotheses have considered genetic factors of immunized individuals and BCG strains, sensitization to environmental mycobacteria and metabolic processes. However, a link has not been established between genetic factors and metabolic processes that may affect the outcome of M. bovis infection and response to BCG vaccination. Herein we used published data linking host cholesterol metabolism with mycobacterial infection, persistence and disease outcome, and results obtained from studies of M. bovis infection and BCG vaccination in the wild boar bTB model to propose a hypothesis: host genetically-defined higher host methylmalonyl-CoA mutase (MUT) expression levels result in lower serum cholesterol concentration and tissue deposits that increase the protective immune response to M. bovis, thus resulting in resistance to bTB and better response to BCG vaccination. If the hypothesis is proven true, these results have important implications for the prevention and treatment of bTB in humans and for the eradication of bTB in wildlife reservoir hosts.

First data on Eurasian wild boar response to oral immunization with BCG and challenge with a Mycobacterium bovis field strain

The Eurasian wild boar (Sus scrofa) is considered a reservoir for bovine tuberculosis (bTB) caused by Mycobacterium bovis and closely related members of the Mycobacterium tuberculosis complex in south-central Spain. The vaccination of wildlife with BCG offers an alternative to culling and to movement restriction for the control of bTB among wildlife reservoirs. In this study, we hypothesized that oral BCG immunization of wild boar would affect the expression of immunoregulatory genes and confer protection against M. bovis. Three groups were used to describe the infection, pathological findings and gene expression profiles in wild boar: BCG-vaccinated and M. bovis-challenged (vaccinated challenged group; N=6), non-vaccinated and M. bovis-challenged (non-vaccinated challenged group; N=4), and non-vaccinated and mock-infected (control group; N=2) animals. M. bovis was isolated from 50% (3/6) and 75% (3/4) of vaccinated challenged and non-vaccinated challenged animals, respectively. All four wild boar from the non-vaccinated challenged group developed bTB-compatible lesions 114 days after challenge. In contrast, only 50% of vaccinated challenged wild boar developed lesions. The PBMC mRNA levels of IL4, RANTES, C3, IFN-gamma and methylmalonyl-CoA mutase (MUT) were analyzed at several days post-vaccination (dpi). When vaccinated challenged animals were compared to controls, all five genes were significantly upregulated at the time of M. bovis infection at 186dpi but IFN-gamma levels were also upregulated at 11 and 46dpi. The C3 and MUT mRNA levels were higher at 46dpi, and 11 and 186dpi, respectively, in vaccinated protected wild boar when compared to non-vaccinated challenged animals. At the end of the experiment (300dpi), the mRNA levels of selected genes were lower in non-vaccinated challenged animals when compared to control wild boar. Exposing wild boar to a dose of 10(4)cfu of M. bovis by the oropharyngeal route is an adequate protocol to produce an infection model in this species. Our results suggested that oral BCG immunization of wild boar results in the upregulation of immunoregulatory genes that may be associated with protective response to M. bovis infection in this species. More studies on vaccine efficacy, delivery, and safety will be needed to confirm if oral vaccination with BCG could be used in bTB control programs for reducing M. bovis infection and clinical disease in wild boar.

Field evaluation of the protective efficacy of Mycobacterium bovis BCG vaccine against bovine tuberculosis

The protective efficacy of Mycobacterium bovis BCG (1 x 10(6) single dose) was evaluated under field conditions. A total of 140 male Holstein Friesian calves, one to two week-old were selected. Two groups of 70 each were formed, one group was vaccinated and the other was injected with a placebo during their second week of age and followed until 12 months of age. The study considered a positive case of tuberculosis to be an animal that had a positive reaction to the three following tests in a row: tuberculin, IFNgamma PPD-B and IFNgamma ESAT6-CFP10 during the 12 months of exposure. The results showed a 59.4% efficacy (IC95%: 47.64-71.16). The non-vaccinated calves were 2.4 times more at risk of becoming infected (IC95%: 1.07-5.68) compared to vaccinated animals. As a complementary test a PCR test was performed using nasal exudates in some animals from both groups using a Mycobacterium complex detection kit. All the positive PCR reactions (5/44) were found in the non-vaccinated animals. These findings suggest that the use of the BCG vaccine, even though it is not capable of protecting 100%, does prevent TB vaccinated animals from excreting bacilli in their nasal secretions at their first year of age.

Antigen mining to define Mycobacterium bovis antigens for the differential diagnosis of vaccinated and infected animals: A VLA perspective

The urgency for new and improved cattle vaccines and diagnostic reagents has been acknowledged by the UK Government, and development of cattle vaccine is a research priority. Significant progress has been made to develop specific antigens that allow the differentiation of bacille Calmette-Guerin (BCG) vaccinated and M. bovis-infected cattle [diagnosis of infected from vaccinated individuals (DIVA) test]. This progress has been greatly facilitated by the completion of the genome sequences of Mycobacterium tuberculosis, M. bovis and BCG Pasteur. In this study, we describe how we applied this knowledge, through comparative genome and transcriptome analysis, to define DIVA antigens that complemented the prototype DIVA antigens ESAT-6 and CFP-10 by increasing their test sensitivity. In addition, we draw general conclusions from our experience, and discuss potential future approaches in this area.

Selective piglet feeders improve age-related bait specificity and uptake rate in overabundant Eurasian wild boar populations

The Eurasian wild boar (Sus scrofa) is a reservoir for pathogens that affect both humans and domestic animals. The control of these diseases requires the development of strategies such as oral vaccination of the reservoir species. The aim of the present study was to determine the species-specific visitation and removal rates of cereal-based baits under field conditions in an overabundant wild boar population. Two different field trials were conducted at a hunting estate. In one trial, baits were placed at track stations set up either randomly in the undeveloped portions of the estate or close to permanent wild boar feeding places. In the second trial, baits were placed in feeders that were selective for use by wild boar piglets. Both trials were conducted in summer 2007 and repeated in spring 2008. No evidence of attractant effect by the bait was found when comparing baited against control stations. A close proximity to the feeders was associated with an increased probability of being visited by wild boar, and piglet feeders were shown to be highly selective for young wild boar. Baits disappeared faster in summer than in spring (i.e. ~70% consumption after the first day in selective feeders in summer, and 40% in spring). Therefore, a combination of a summer season and selective feeders was found to be a potentially reliable bait-deployment strategy for wild boar juveniles under Mediterranean conditions. These results support the use of selective feeders for oral delivery of baits to 2–4-month-old wild boar piglets, which is the preferred age for vaccination. Our delivery technique based on selective piglet feeders also has potential for other uses in the Eurasian wild boar and wild pigs under different management conditions.

Immunological responses and protective immunity in BCG vaccinated badgers following endobronchial infection with Mycobacterium bovis

European badgers (Meles meles) are a reservoir host of Mycobacterium bovis and are implicated in the transmission of tuberculosis to cattle in Ireland and Great Britain. The development of a vaccine for use in badgers is considered a key element of any campaign to eradicate the disease in livestock in both countries. In this study we have vaccinated groups of badgers with approximately 5 x 10(5)cfu of the BCG vaccine delivered via two alternative routes, subcutaneous and mucosal (intranasal/conjunctival). Following experimental endobronchial infection with approximately 10(4)cfu of M. bovis, all badgers were euthanised at 12 weeks post-infection. At post-mortem examination both vaccinated groups had significantly reduced severity of disease compared with the non-vaccinated controls. The analysis of immune responses throughout the study showed that vaccination with BCG did not generate any detectable immunological responses as measured by IFN-gamma production in antigen-stimulated peripheral blood mononuclear cells (PBMC) and IgG serological responses. However, the levels of the responses increased following M. bovis infection, and the kinetic profiles corresponded to the severity of lesions recorded post-mortem. Significant differences were observed in the timing of development of the immune responses between vaccinates and controls. The results suggest that the immunological responses are associated with the levels of protective immunity and could be used as markers to monitor control of disease in badgers following vaccination.

Oral vaccination of guinea pigs with a Mycobacterium bovis bacillus Calmette-Guerin vaccine in a lipid matrix protects against aerosol infection with virulent M. bovis

Increased incidence of bovine tuberculosis (TB) in the United Kingdom caused by infection with Mycobacterium bovis is a cause of considerable economic loss to farmers and the government. The Eurasian badger (Meles meles) represents a wildlife source of recurrent M. bovis infections of cattle in the United Kingdom, and its vaccination against TB with M. bovis bacillus Calmette-Guérin (BCG) is an attractive disease control option. Delivery of BCG in oral bait holds the best prospect for vaccinating badgers over a wide geographical area. Using a guinea pig pulmonary challenge model, we evaluated the protective efficacy of candidate badger oral vaccines, based on broth-grown or ball-milled BCG, delivered either as aqueous suspensions or formulated in two lipids with differing fatty acid profiles (one being animal derived and the other being vegetable derived). Protection was determined in terms of increasing body weight after aerosol challenge with virulent M. bovis, reduced dissemination of M. bovis to the spleen, and, in the case of one oral formulation, restricted growth of M. bovis in the lungs. Only oral BCG formulated in lipid gave significant protection. These data point to the potential of the BCG-lipid formulation for further development as a tool for controlling tuberculosis in badgers.

Enhanced protection against bovine tuberculosis after coadministration of Mycobacterium bovis BCG with a Mycobacterial protein vaccine-adjuvant combination but not after coadministration of adjuvant alone

Current efforts are aimed at optimizing the protective efficacy of Mycobacterium bovis BCG by the use of vaccine combinations. We have recently demonstrated that the protection afforded by BCG alone is enhanced by vaccinating cattle with a combination of vaccines comprising BCG and a protein tuberculosis vaccine, namely, culture filtrate proteins (CFPs) from M. bovis plus an adjuvant. In the current study, three different adjuvant systems were compared. The CFP was formulated with a depot adjuvant, dimethyldioctadecyl ammonium bromide (DDA), together with one of three different immunostimulants: monophosphoryl lipid A (MPL), a synthetic mycobacterial phosphatidylinositol mannoside-2 (PIM2), and a synthetic lipopeptide (Pam3Cys-SKKKK [Pam(3)CSK(4)]). Groups of cattle (n = 10/group) were vaccinated with BCG-CFP-DDA-PIM2, BCG-CFP-DDA-MPL, or BCG-CFP-DDA-Pam(3)CSK(4). Two additional groups (n = 10) were vaccinated with BCG alone or BCG-adjuvant (DDA-MPL), and a control group was left unvaccinated. Protection was assessed by challenging the cattle intratracheally with M. bovis. Groups of cattle vaccinated with BCG-CFP-DDA-PIM2, BCG-CFP-DDA-MPL, BCG-CFP-DDA-Pam(3)CSK(4), and BCG alone showed significant reductions in three, three, five, and three pathological and microbiological disease parameters, respectively, compared to the results for the nonvaccinated group. Vaccination with the combination of BCG and the DDA-MPL adjuvant alone abrogated the protection conferred by BCG alone. The profiling of cytokine gene expression following vaccination, prior to challenge, did not illuminate significant differences which could explain the latter result. Vaccination of cattle with a combination of BCG and protein tuberculosis vaccine enhances protection against tuberculosis.

Adverse reactions to Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccination against tuberculosis in humans, veterinary animals and wildlife species

The Mycobacterium bovis strain, bacille Calmette-Guérin (BCG) is one of the most widely used human vaccines and remains one of the safest vaccines available. It has been used in human populations for over 80 years and 100 million children receive the vaccine annually. It has also been employed extensively for vaccine studies in laboratory animal hosts and is currently being developed for use in a variety of livestock and wild animals. Despite the large number of doses delivered since is first usage in 1921, reports of adverse reactions arising from the use of the BCG vaccine are relatively uncommon and where serious reactions do occur they are often the result of vaccination of immuno-compromised individuals. Factors that may influence the development of adverse reactions to BCG include the potency and dose of the vaccine strain, the route of delivery, the age and immune status of the host, and the skill levels of the operator administering the vaccine. Circumstances affecting the notification of adverse reactions include the lack of clear case definitions of abnormal vaccine reactions, and a scarcity of systematic surveillance and functioning reporting systems. With continued use of the BCG and the development of a new generation of prophylactic and therapeutic vaccines against tuberculosis in different host species, the risk factors associated with adverse reactions may need to be reappraised.

Differential expression of inflammatory and immune response genes in mesenteric lymph nodes of Iberian red deer (Cervus elaphus hispanicus) naturally infected with Mycobacterium bovis

Little information is available about gene expression in natural mycobacterial infection of wildlife species. Iberian red deer can serve as reservoir of Mycobacterium bovis in Spain, thus increasing the risk of bovine tuberculosis (bTB) in humans and cattle. Herein, we characterized the differential expression of inflammatory and immune response genes in mesenteric lymph nodes of deer naturally infected with M. bovis using microarray hybridization. Results were validated by determination of serum protein concentrations and/or real-time RT-PCR. Of the 600 genes that were analyzed in the microarray, 17 genes displayed an expression fold change greater than 1.7 in infected or uninfected deer (P0.05). These genes included tight junction proteins, IL-11R, bactenecin, CD62L, CD74, desmoglein, IgA and IgM that constitute new findings and suggest new mechanisms by which M. bovis may modulate host inflammatory and immune responses. These results contribute to our basic understanding of the mechanisms of pathogenesis and immunity to natural mycobacterial infections and may have important implications for the control of bTB.

Comparative genomics and proteomics to study tissue-specific response and function in natural Mycobacterium bovis infections

Bovine tuberculosis (bTB) is an established zoonotic disease which affects cattle and wildlife worldwide and new strategies are required to control and eradicate the disease. The European wild boar (Sus scrofa) is a major reservoir of bTB in Spain. The objective of this paper was to review tissue-specific response and function of mandibular lymph nodes (MLN) and oropharyngeal tonsils (OT) in European wild boar naturally infected with Mycobacterium bovis. Genomics and proteomics data were used to compare differential gene expression and global protein patterns in OT and MLN of M. bovis-infected and uninfected European wild boar and the results were analyzed considering previous reports of experimental infections in laboratory and domestic animals. The results showed tissue-specific differences in OT and MLN in response to M. bovis infection. Tissue-specific differences in gene expression and protein profiles suggested different functions for OT and MLN during mycobacterial infection and provided information to characterize the pathobiology of M. bovis infection in European wild boar with important implications for the control of bTB in Spain. The characterization of molecular events in tissues that play different roles during mycobacterial infection in naturally infected individuals may be relevant to understand the pathobiology of M. bovis infection and to design effective strategies for the control of bTB in wildlife reservoirs.

Vaccination of white-tailed deer (Odocoileus virginianus) with Mycobacterium bovis bacillus Calmette Guerín

Wildlife reservoirs of Mycobacterium bovis represent serious obstacles to the eradication of tuberculosis in domestic livestock. In Michigan, USA tuberculous white-tailed deer transmit M. bovis to cattle. One approach in dealing with this wildlife reservoir is to vaccinate deer in order to interrupt the cycle of deer to deer and deer to cattle transmission. Thirty-one white-tailed deer were assigned to one of three groups; 2 SC doses of 10(7)CFU of M. bovis BCG (n=11); 1 SC dose of 10(7)CFU of M. bovis BCG (n=10); or unvaccinated deer (n=10). After vaccination, deer were inoculated intratonsilarly with 300 CFU of virulent M. bovis. Gross lesion severity scores of the medial retropharyngeal lymph node were significantly reduced in deer receiving 2 doses of BCG compared to unvaccinated deer. Vaccinated deer had fewer lymph node granulomas than unvaccinated deer, and most notably, fewer late stage granulomas characterized by coalescent caseonecrotic granulomas containing numerous acid-fast bacilli. BCG was isolated from 7/21 vaccinated deer as long as 249 days after vaccination. In one case BCG was transmitted from a vaccinated deer to an unvaccinated deer. In white-tailed deer BCG provides measurable protection against challenge with virulent M. bovis. However, persistence of vaccine within tissues as well as shedding of BCG from vaccinates remain areas for further investigation.

A new attenuated Mycobacterium bovis vaccine protects brushtail possums (Trichosurus vulpecula) against experimental tuberculosis infection

Vaccination of wildlife against bovine tuberculosis is being actively considered in countries that have wildlife reservoirs of Mycobacterium bovis infection. A newly attenuated strain of M. bovis (WAg533) was produced as part of a programme to develop a better vaccine than BCG to control tuberculosis in brushtail possums in New Zealand. The vaccine efficacy of WAg533 in possums was compared to BCG using three different methods of inoculation (conjunctival/intranasal, oral and sub-cutaneous) followed by aerosol challenge. Overall, WAg533 was a more potent vaccine than BCG and by two methods of inoculation gave more measures of protection that were significantly different from controls.

An ESAT-6:CFP10 DNA vaccine administered in conjunction with Mycobacterium bovis BCG confers protection to cattle challenged with virulent M. bovis

The potency of genetic immunization observed in the mouse has demonstrated the utility of DNA vaccines to induce cell-mediated and humoral immune responses. However, it has been relatively difficult to generate comparable responses in non-rodent species. The use of molecular adjuvants may increase the magnitude of these suboptimal responses. In this study, we demonstrate that the co-administration of plasmid-encoded GM-CSF and CD80/CD86 with a novel ESAT-6:CFP10 DNA vaccine against bovine tuberculosis enhances antigen-specific cell-mediated immune responses. ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA vaccinated animals exhibited significant (p<0.01) antigen-specific proliferative responses compared to other DNA vaccinates. Increased expression (p< or =0.05) of CD25 on PBMC from ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA vaccinates was associated with increased proliferation, as compared to control DNA vaccinates. Significant (p<0.05) numbers of ESAT-6:CFP10-specific IFN-gamma producing cells were evident from all ESAT-6:CFP10 DNA vaccinated animals compared to control DNA vaccinates. However, the greatest increase in IFN-gamma producing cells was from animals vaccinated with ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA. In a low-dose aerosol challenge trial, calves vaccinated as neonates with Mycobacterium bovis BCG and ESAT-6:CFP10+GM-CSF+CD80/CD86 DNA exhibited decreased lesion severity in the lung and lung-associated lymph nodes following viruluent M. bovis challenge compared to other vaccinated animals or non-vaccinated controls. These data suggest that a combined vaccine regimen of M. bovis BCG and a candidate ESAT-6:CFP10 DNA vaccine may offer greater protection against tuberculosis in cattle than vaccination with BCG alone.

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.

Proteomic and transcriptomic analyses of differential stress/inflammatory responses in mandibular lymph nodes and oropharyngeal tonsils of European wild boars naturally infected with Mycobacterium bovis

Differential stress/inflammatory responses were characterized at the mRNA and protein levels in mandibular lymph nodes (MLN) and oropharyngeal tonsils of European wild boars (Sus scrofa), naturally infected with Mycobacterium bovis. Suppression-subtractive hybridization combined with immunohistochemistry and/or quantitative real-time RT-PCR were used to identify and characterize abundant stress/inflammatory gene sequences differentially expressed in tuberculous (TB+) wild boars. Genes identified in MLN and tonsils corresponded to serum amyloid A, arginase I, osteopontin, lysozyme, annexin I, and heat shock proteins, respectively. Global protein patterns in MLN and tonsils were compared between TB+ and nontuberculous (TB-) boars by 2-DE and MALDI-TOF MS. Five proteins, including stress/inflammatory proteins annexin V, serum albumin, and apolipoprotein A1 were found at lower levels in MLN of TB+ boars. Manganese superoxide dismutase was found up-regulated in MLN of TB+ boars. Five proteins, including creatine kinase and MHC class II antigens were found up-regulated in tonsils of TB+ boars. These results demonstrated differential stress/inflammatory responses in wild boars naturally infected with M. bovis and suggest possible markers of tuberculosis in this species that may prove useful for future studies of host-pathogen interactions and for diagnostics and vaccine development.

The immunology of bovine tuberculosis and progression toward improved disease control strategies

Failure to remove cattle diseased with Mycobacterium bovis has immense financial implications for disease control, animal health and agricultural trade as well as the zoonotic risk to human health. Current disease control strategies based on DTH skin testing fail to detect all diseased cattle and additional measures are urgently needed to improve detection of disease and to prevent naïve animals becoming exposed to infection. Experimental models of bovine TB traditionally based on intra-nasal instillation, intra-tracheal inoculation or placed in-contact with infected cattle, have been further developed using aerosolised bacteria delivered to the respiratory tract, allowing field-like bovine TB to be recreated under controlled, experimental conditions. Experimental infection models have already been used to improve diagnostic tests. Specificity of DTH skin testing can be improved under experimental conditions, using recombinant ESAT-6, while laboratory assays such as IFN-gamma release have benefited from the use of defined proteins to improve assay specificity. In combination, antigen cocktails may also improve test sensitivity. There is a concerted international effort to evaluate vaccines for use in cattle populations and to define vaccination strategies which will eliminate disease from infected herds. DNA, protein and genetically modified vaccines inoculated in a single dose, given as prime-boost or injected concurrently, will elicit significant protection against challenge with M. bovis under controlled conditions. However, vaccines and vaccination strategies require evaluation under field conditions. Furthermore, complementary strategies are under development to differentiate immune responses that follow vaccination from those following disease. This paper describes those recent advances which may lead to the introduction of improved disease control strategies.

DNA vaccines against mycobacterial diseases

Plasmid DNA vaccination is a very powerful and easy method for the induction of strong humoral and cell-mediated immune responses in mice. The technique has also been successfully applied for the definition of immunodominant, human T-cell epitopes using HLA-transgenic mice. By virtue of its strong capacity to induce CD4+-mediated Th1 and CD8+-mediated cytotoxic T-lymphocyte responses, this vaccine approach is particularly attractive for the prophylaxis of intracellular pathogens, such as Mycobacterium tuberculosis (TB) and other pathogenic mycobacteria. In small rodents, the potential of mycobacterial DNA vaccines is well established. In humans, DNA vaccines are clearly less immunogenic and, so far, TB-specific DNA vaccines have not been assessed in humans. However, a number of studies in cattle and sheep have demonstrated the potential of mycobacterial DNA vaccines in larger animals. Also, immunization protocols combining the potent priming capacity of plasmid DNA with subsequent boosting with recombinant protein, recombinant pox-viruses or with Mycobacterium bovis bacille Calmette-Guerin (BCG) vaccine are particularly promising for future applications. The potential of mycobacterial DNA vaccines for immunotherapy and post-exposure prophylaxis is still not clear.