Vaccination of the badger (Meles meles) against Mycobacterium bovis

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.

Tuberculosis and badgers: new approaches to diagnosis and control

The Eurasian badger (Meles meles) is considered to be an important wildlife reservoir of Mycobacterium bovis infection for cattle in Ireland and in Great Britain. The inability to eradicate the disease from cattle is, in part, a consequence of M. bovis infection in badgers sharing the environment with cattle. Whereas national tuberculosis eradication programmes continue to be effective in maintaining the disease prevalence in cattle at a low level, strategies to control and eradicate tuberculosis in badgers remain constrained by a lack of reagents and rapid tests to diagnose tuberculosis infection in live badgers. However, the development of rational control measures for both badgers and cattle can be achieved by detailed epidemiological analysis combining immunological testing and strain typing with current developments in information technology and geographical information systems. This allows for construction of detailed profiles of tuberculosis episodes which can identify the nature of the outbreak, its likely origin and future spread. The identification of critical areas for control then permits the strategic allocation of resources based on analysis of disease patterns in cattle and badgers. Targeted vaccination of badgers is an option which could facilitate the elimination of disease in affected areas.

Experimental infection of brushtail possums (Trichosurus vulpecula) with Mycobacterium bovis by conjunctival instillation

In New Zealand, the brushtail possum (Trichosurus vulpecula) is the major wildlife reservoir of Mycobacterium bovis. Procedures for experimentally infecting possums are required to study the pathogenesis of the disease and to challenge possums in vaccine efficacy studies. Conjunctival instillation of a suspension of M. bovis was effective in producing bovine tuberculosis in captive possums. The experimental disease progressed slowly with the development of palpable lesions in superficial lymph node lesions, both characteristics of the disease in wild, naturally infected possums. At necropsy there was widespread distribution of macroscopic and microscopic lesions. The proportion of possums that became diseased, the rate of development and severity of lesions, the severity of clinical signs, all increased when the dose of M. bovis was increased. Of the three doses used, the medium dose (1000-2000 colony forming units) produced the disease with the most desired characteristics. As a procedure for exposing possums to infection with M. bovis the conjunctival route has advantages in that it is simple and safe to perform, and possums need only to be sedated for infection.

Vaccinating badgers (Meles meles) against Mycobacterium bovis: the ecological considerations

Bovine tuberculosis (TB) is a serious zoonotic disease, which despite a largely successful test and slaughter programme has persisted in cattle herds in parts of the UK. The badger (Meles meles) is widely considered to represent a significant wildlife reservoir for the transmission of Mycobacterium bovis to cattle, and has been the subject of a variety of culling strategies since the mid 1970s. Nevertheless, the incidence of herd breakdowns has continued to rise, and the efficacy of culling is currently the subject of a large-scale field trial. One potential alternative tool for the management of disease in wildlife populations is vaccination. However, the successful development of an effective vaccine and a strategy for its delivery will require careful consideration of the practical constraints imposed by ecological factors. In the current paper, we discuss relevant ecological and epidemiological characteristics of badger populations and practical aspects of vaccine delivery in the field.

The efficacy of bacille Calmette-Guérin vaccine in wild brushtail possums (Trichosurus vulpecula)

A population of wild brushtail possums (Trichosurus vulpecula) in which bovine tuberculosis was endemic was vaccinated with live bacille Calmette-Guérin (BCG) to determine the efficacy of vaccination. The population on the 56 hectare site was monitored bimonthly over 2 years using a capture-release regime. During the study tuberculosis was diagnosed by clinical and post mortem examination. Possums were vaccinated with BCG by both intranasal aerosol and conjunctival instillation. Possums were revaccinated on average every 5 months. Over the 2 years, 300 possums were recruited to the study with 149 being allocated to the vaccination group. There were significantly fewer cases of tuberculosis in the vaccinated (4 cases) than in the unvaccinated group (13 cases; P=0.023). The vaccine efficacy was 69%. An attempt was made to increase the incidence of disease by releasing onto the site possums that had been experimentally infected with a strain of M. bovis unknown in the area. However, this did not result in any additional cases. BCG vaccine was shown to have a level of efficacy which could be of assistance in controlling tuberculosis in wild possum populations. The future use of vaccination for the control of tuberculosis in wild possum populations is discussed.

Vaccination of the brushtail possum (Trichosurus vulpecula) against Mycobacterium bovis infection with bacille Calmette-Guérin: the response to multiple doses

In New Zealand, the brushtail possum (Trichosurus vulpecula) is the principal wildlife vector of bovine tuberculosis. Control of infected possum populations contributes to the control of tuberculosis in domestic livestock. Vaccination is potentially a complementary strategy to population control, but to be cost-effective, administration of the vaccine to possums would need to be from an appropriately designed automatic vaccinator. Possums themselves would activate the vaccinator so that it would deliver an aerosol spray of vaccine. There would be no direct way to prevent possums receiving multiple doses of vaccine. This study examined the effect on protective immunity of repeated vaccination. Captive possums were vaccinated with BCG strain pasteur 1173P2 either 12 times at weekly intervals, twice at 6-weekly intervals, or once. Vaccination was by a combination of intranasal aerosol and conjunctival instillation. Eight weeks after the last dose of vaccine, all possums were challenged intratracheally with Mycobacterium bovis strain 83/6235. Vaccination induced a significant immune response as measured by the lymphocyte proliferation assay (LPA). A significant level of protection, as measured by the response to challenge, developed in all the vaccinated possum groups, but protection was greatest in the group vaccinated 12 times. It was concluded that protection would be enhanced if vaccinations were repeated at short intervals (weekly), but no benefit or detriment resulted from revaccination after longer intervals (1-2 months).

Models of Mycobacterium bovis in wildlife and cattle

Following the first model of wildlife tuberculosis (in European badgers) there has been a spate of papers modelling wildlife TB. These have looked at population parameters and disease dynamics in the badger and possum. Recent papers in particular have looked at various methods of controlling the wildlife vector to reduce the incidence of TB in cattle. The author examines the role of modelling to show what insights it has given us, which issues have not been addressed, and where the shortfalls lie. Particular attention will be paid to a comparison between models of badgers and possums, and between simple and more complex models, and possible areas of future research will be revealed.

A coordinated strategy for evaluating new vaccines for human and animal tuberculosis

There is a remarkable convergence in the current efforts to develop and evaluate new tuberculosis (TB) vaccine candidates for use in humans, domestic animals, and wild animal reservoirs. It is quite likely that similar vaccination strategies will prove useful in these diverse host species. Many TB vaccine candidates are being screened for protective efficacy in conventional laboratory animals (e.g. mouse, guinea pig), in captive wild species under laboratory conditions (e.g. brushtail possum), and in the target hosts (e.g. cattle, deer). These systems share some important features, e.g. direct challenge infection of the lung by intratracheal or aerosol exposure, and the use of bacterial enumeration, and gross and microscopic histopathology, as the readouts. Some TB vaccine candidates have been tested in many models, yielding important insights into common mechanisms of resistance to Mycobacterium tuberculosis and M. bovis, and providing evidence of the vaccine's ability to induce protection under widely different circumstances. Coordination of this global search for better TB vaccines, irrespective of target species, would facilitate the rapid application of new technologies and maximize the sharing of materials and experiences between human and veterinary TB researchers. The creation of liaisons between TB vaccine research efforts of government-sponsored medical and agricultural research programs, international bodies such as the World Health Organization (WHO) and the European Community (EC), private foundations and the vaccine industry, will yield a high return.

Aerosol vaccination of the brushtail possum (Trichosurus vulpecula) with bacille Calmette–Guérin: the duration of protection

Bovine tuberculosis is endemic in wild brushtail possums (Trichosurus vulpecula) in New Zealand. The disease is controlled by reducing or eliminating infected possum populations, but control methods do not kill all possums in the targeted area, leaving some tuberculous possums to maintain the disease. Vaccination with bacille Calmette-Guérin (BCG) has been shown to provide significant levels of protection. Vaccination is a potential alternative or complementary control strategy if protection is long lasting. Captive possums were vaccinated with a single dose of BCG by intranasal aerosol and challenged by intratracheal instillation of Mycobacterium bovis 2, 6 or 12 months after vaccination. Vaccination produced significant immunity as measured by the lymphocyte proliferative response to bovine PPD and protection in response to challenge. The protective response was seen as a decrease in the mass of pulmonary lesions and decreased dissemination to the abdominal organs and body lymph nodes. The protective effect was strongest at 2 months after vaccination but was still present at a lower level at 12 months. Delivery of an aerosol vaccine to possums in the wild using a self-delivery system could contribute substantially to wildlife tuberculosis control.

The development of wildlife control strategies for eradication of tuberculosis in cattle in Ireland

Wildlife species, such as badgers, act as maintenance hosts for Mycobacterium bovis and contribute to the spread and persistence of tuberculosis in associated cattle populations. In areas in which there is a tuberculosis problem affecting a number of herds, the involvement of infected wildlife in the introduction of M. bovis infection into herds act as a constraint to eradication of the disease. Epidemiological evidence demonstrates a high prevalence of tuberculosis in badgers, and controlled studies involving comprehensive badger removal have shown that this strategy can serve to significantly reduce cattle reactor rates in the targeted areas. However, as the badger is a protected wildlife species, alternative strategies are required to combat the disease. Targeted vaccination of wildlife species against tuberculosis is an option which, if successfully employed, could directly facilitate the advancement of bovine tuberculosis eradication in affected areas. Any proposed vaccination programme would need to be undertaken against the background of an exhaustive investigation of the cattle and herd management-related factors, and take account of environmental issues.

Identification of a novel DNA probe for strain typing Mycobacterium bovis by restriction fragment length polymorphism analysis

Bovine tuberculosis caused by Mycobacterium bovis remains a significant disease of farmed cattle in many countries despite ongoing tuberculosis eradication programs. Molecular typing methods such as restriction fragment length polymorphism (RFLP) analysis and spoligotyping have been used to identify related herd breakdowns in an attempt to identify more precisely the route of infection into cattle herds and to trace the transmission of bovine tuberculosis. A recent geographical survey of Irish M. bovis isolates demonstrated that a significant proportion of isolates ( approximately 20%) exhibit a common strain type, limiting the value of current strain typing methods as an epidemiological tool. We have identified and cloned a region of the M. bovis genome, pUCD, which generates a clear, highly polymorphic banding pattern when used as an RFLP probe on AluI restriction-digested M. bovis genomic DNA and which effectively subdivides this common strain type. When used to type 60 Irish M. bovis isolates, pUCD exhibited greater discriminatory power than the commonly used mycobacterial RFLP probes IS6110, PGRS, and DR and detected an equivalent number of strain types to a combination of these three probes. pUCD also detected significantly more strain types than the spoligotyping technique, while maintaining a high level of concordance between epidemiologically related and unrelated herd breakdowns. The polymorphic element within pUCD remains to be fully characterized, however the potential for this probe to greatly decrease the workload necessary to genotype M. bovis by RFLP analysis is compelling.

Immunological approaches to the control of tuberculosis in wildlife reservoirs

Attempts to eradicate tuberculosis from cattle and farmed deer in some countries have been frustrated by the existence of wildlife reservoirs of Mycobacterium bovis infection. Possum control programmes in New Zealand using poisons have shown clearly that the brushtail possum is an important source of infection for cattle and farmed deer, and the sum of evidence strongly suggests that badgers serve as a source of infection for cattle in the UK. Bovine tuberculosis can only be eradicated from these countries by controlling M. bovis infection in both wildlife and domestic animals. The most promising options for control of M. bovis infection in wildlife in the longer term include the development of a tuberculosis vaccine for wildlife and a strategy for biological control of possums. The aim of this review is to address the problems and approaches involved in the control of wildlife tuberculosis from an immunological perspective.