Reduced spillover transmission of Mycobacterium bovis to feral pigs (Sus scofa) following population control of brushtail possums (Trichosurus vulpecula)

Presence of Foodborne Bacteria in Wild Boar and Wild Boar Meat-A Literature Survey for the Period 2012-2022

The wild boar is an abundant game species with high reproduction rates. The management of the wild boar population by hunting contributes to the meat supply and can help to avoid a spillover of transmissible animal diseases to domestic pigs, thus compromising food security. By the same token, wild boar can carry foodborne zoonotic pathogens, impacting food safety. We reviewed literature from 2012-2022 on biological hazards, which are considered in European Union legislation and in international standards on animal health. We identified 15 viral, 10 bacterial, and 5 parasitic agents and selected those nine bacteria that are zoonotic and can be transmitted to humans via food. The prevalence of Campylobacter, Listeria monocytogenes, Salmonella, Shiga toxin-producing E. coli, and Yersinia enterocolitica on muscle surfaces or in muscle tissues of wild boar varied from 0 to ca. 70%. One experimental study reported the transmission and survival of Mycobacterium on wild boar meat. Brucella, Coxiella burnetii, Listeria monocytogenes, and Mycobacteria have been isolated from the liver and spleen. For Brucella, studies stressed the occupational exposure risk, but no indication of meat-borne transmission was evident. Furthermore, the transmission of C. burnetii is most likely via vectors (i.e., ticks). In the absence of more detailed data for the European Union, it is advisable to focus on the efficacy of current game meat inspection and food safety management systems.

The importance of long-term studies on wildlife diseases and their interfaces with humans and domestic animals: A review

Long-term wildlife disease research (LTWDR) and its interfaces with humans and domestic animals provide perspective to understand the diseases' main drivers and how they operate. In a systematic review, we analysed the temporal trend of the studies on LTWDR, their aims, and the hosts, pathogens and geographic areas studied. We also evaluated the added value that such studies provide. For analysis, we selected a total of 538 articles from 1993 to 2017 with a study period greater than or equal to 4 consecutive years. A marked increase in the number of studies published during the last 20 years was observed that reflects a growing awareness of the outstanding role of wildlife as a reservoir of diseases. The most studied pathogen agents were viruses (39.2%), bacteria (38.5%) and protozoans (15.8%). Concerning the hosts, mammals (84.9%), particularly ungulates (40%) and carnivores (30.9%), and birds (12.5%) were the most represented in these long-term studies. Most articles reached conclusions concerning the effect of the disease on the infection/host dynamics (98.7%) and over 40% considered the economic consequences or proposed management and control measures. The research was mainly located in the Northern Hemisphere. While the definition of LTWDR is not only determined by the duration of the monitoring, the study must be long enough to: (a) address ecological and epidemiological questions that cannot be resolved with short-term observations or experiments, and (b) clarify the effects of different drivers. This review demonstrates that LTWDR has provided information about the causes and consequences of disease change that otherwise could not have been obtained. It may be used to inform decisions related to the emergence of disease and might help to design early warning systems of disease based on retrospective investigations.

Wild Animal Tuberculosis: Stakeholder Value Systems and Management of Disease

When human health is put at risk from the transmission of animal diseases, the options for intervention often require input from stakeholders whose differing values systems contribute to decisions on disease management. Animal tuberculosis (TB), caused principally by Mycobacterium bovis is an archetypical zoonotic pathogen in that it can be transmitted from animals to humans and vice versa. Although elimination of zoonotic transmission of TB to humans is frequently promoted as the raison d'être for TB management in livestock, in many countries the control strategies are more likely based on minimizing the impact of sustained infection on the agricultural industry. Where wild animals are implicated in the epidemiology of the disease, the options for control and eradication can require involvement of additional stakeholder groups. Conflict can arise when different monetary and/or societal values are assigned to the affected animals. This may impose practical and ethical dilemmas for decision makers where one or more species of wild animal is seen by some stakeholders to have a greater value than the affected livestock. Here we assess the role of stakeholder values in influencing TB eradication strategies in a number of countries including Ireland, the UK, the USA, Spain, France, Australia, New Zealand and South Africa. What it reveals is that the level of stakeholder involvement increases with the complexity of the epidemiology, and that similar groups of stakeholders may agree to a set of control and eradication measures in one region only to disagree with applying the same measures in another. The level of consensus depends on the considerations of the reservoir status of the infected host, the societal values assigned to each species, the type of interventions proposed, ethical issues raised by culling of sentient wild animals, and the economic cost benefit effectiveness of dealing with the problem in one or more species over a long time frame. While there is a societal benefit from controlling TB, the means to achieve this requires identification and long-term engagement with all key stakeholders in order to reach agreement on ethical frameworks that prioritize and justify control options, particularly where culling of wild animals is concerned.

Roll-Back Eradication of Bovine Tuberculosis (TB) From Wildlife in New Zealand: Concepts, Evolving Approaches, and Progress

The New Zealand government and agricultural industries recently jointly adopted the goal of nationally eradicating bovine tuberculosis (TB) from livestock and wildlife reservoirs by 2055. Only Australia has eradicated TB from a wildlife maintenance host. Elsewhere the disease is often self-sustaining in a variety of wildlife hosts, usually making eradication an intractable problem. The New Zealand strategy for eradicating TB from wildlife is based on quantitative assessment using a Bayesian “Proof of Freedom” framework. This is used to assess the probability that TB has been locally eradicated from a given area. Here we describe the framework (the concepts, methods and tools used to assess TB freedom and how they are being applied and updated). We then summarize recent decision theory research aimed at optimizing the balance between the risk of falsely declaring areas free and the risk of overspending on disease management when the disease is already locally extinct. We explore potential new approaches for further optimizing the allocation of management resources, especially for places where existing methods are impractical or expensive, including using livestock as sentinels. We also describe how the progressive roll-back of locally eradicated areas scales up operationally and quantitatively to achieve and confirm eradication success over the entire country. Lastly, we review the progress made since the framework was first formally adopted in 2011. We conclude that eradication of TB from New Zealand is feasible, and that we are well on the way to achieving this outcome.

Low-dose BCG vaccination protects free-ranging cattle against naturally-acquired bovine tuberculosis

Vaccination of cattle with Mycobacterium bovis BCG has been shown to protect against infection with virulent strains of M. bovis, and against resultant bovine tuberculosis (TB). Here we report on a large-scale trial in New Zealand where free-ranging cattle were vaccinated with 3 x 10⁵ BCG via injection, a lower dose than any previously trialed in cattle against exposure to a natural force of M. bovis infection. In a multi-year enrolment study involving >800 animals, three cohorts of 1-2 year old cattle were randomised to receive vaccine or to serve as non-vaccinated controls. Cattle were slaughtered and subject to standard abattoir post mortem examination for M. bovis culture-positive TB lesions after up to 3.7 years of in-field exposure; additionally, lymph node samples from approximately half of the cattle were examined further to identify infection in the absence of lesions. Overall TB prevalence, as identified by gross lesions detected at slaughter, was low among farmed cattle at the study site (<4% annually). There were two lesioned cases among 520 vaccinated trial cattle (0.38%) compared to eight among 297 non-vaccinated trial cattle (2.69%). Trial vaccine efficacy was 85.7% against abattoir-detectable TB (statistically significant protection), and 86.7% when adjusted for duration of exposure. BCG vaccination did not significantly affect the response rates of cattle to ante mortem skin- or blood-tests in diagnostic tests conducted >7 months post-vaccination. Use of a reduced, yet effective, dose of BCG would increase the cost effectiveness of using this vaccine in a bovine TB control programme.

Efficacy of oral BCG vaccination in protecting free-ranging cattle from natural infection by Mycobacterium bovis

Vaccination of cattle against bovine tuberculosis could be a valuable control strategy, particularly in countries faced with intractable ongoing infection from a disease reservoir in wildlife. A field vaccination trial was undertaken in New Zealand. The trial included 1286 effectively free-ranging cattle stocked at low densities in a remote 7600ha area, with 55% of them vaccinated using Mycobacterium bovis BCG (Danish strain 1311). Vaccine was administered orally in all but 34 cases (where it was injected). After inclusion, cattle were exposed to natural sources of M. bovis infection in cattle and wildlife, most notably the brushtail possum (Trichosurus vulpecula). Cattle were slaughtered at 3-5 years of age and were inspected for tuberculous lesions, with mycobacteriological culture of key tissues from almost all animals. The prevalence of M. bovis infection was 4.8% among oral BCG vaccinates, significantly lower than the 11.9% in non-vaccinates. Vaccination appeared to both reduce the incidence of detectable infection, and to slow disease progression. Based on apparent annual incidence, the protective efficacy of oral BCG vaccine was 67.4% for preventing infection, and was higher in cattle slaughtered soon after vaccination. Skin-test reactivity to tuberculin was high in vaccinates re-tested 70days after vaccination but not in non-vaccinates, although reactor animals had minimal response in gamma-interferon blood tests. In re- tests conducted more than 12 months after vaccination, skin-test reactivity among vaccinates was much lower. These results indicate that oral BCG vaccination could be an effective tool for greatly reducing detectable infection in cattle.

Field Trial of an Aerially-Distributed Tuberculosis Vaccine in a Low-Density Wildlife Population of Brushtail Possums (Trichosurus vulpecula)

Oral-delivery Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine in a lipid matrix has been shown to confer protection against M. bovis infection and reduce the severity of tuberculosis (TB) when fed to brushtail possums (Trichosurus vulpecula), the major wildlife vector of bovine TB in New Zealand. Here we demonstrate the feasibility of aerial delivery of this live vaccine in bait form to an M. bovis-infected wild possum population, and subsequently assess vaccine uptake and field efficacy. Pre-trial studies indicated a resident possum population at very low density (<0.6 possums/ha) at the field site, with a 5.1% prevalence of macroscopic TB lesions. Pilot studies indicated that flavoured lipid matrix baits in weather-proof sachets could be successfully sown aerially via helicopter and were palatable to, and likely to be consumed by, a majority of wild possums under free-choice conditions. Subsequently, sachet-held lipid baits containing live BCG vaccine were sown at 3 baits/ha over a 1360 ha area, equating to >5 baits available per possum. Blood sampling conducted two months later provided some evidence of vaccine uptake. A necropsy survey conducted one year later identified a lower prevalence of culture-confirmed M. bovis infection and/or gross TB lesions among adult possums in vaccinated areas (1.1% prevalence; 95% CI, 0–3.3%, n = 92) than in unvaccinated areas (5.6%; 0.7–10.5%, n = 89); P = 0.098. Although not statistically different, the 81% efficacy in protecting possums against natural infection calculated from these data is within the range of previous estimates of vaccine efficacy in trials where BCG vaccine was delivered manually. We conclude that, with further straightforward refinement to improve free-choice uptake, aerial delivery of oral BCG vaccine is likely to be effective in controlling TB in wild possums. We briefly discuss contexts in which this could potentially become an important complementary tool in achieving national eradication of TB from New Zealand wildlife.

Epidemiology and control of Mycobacterium bovis infection in brushtail possums (Trichosurus vulpecula), the primary wildlife host of bovine tuberculosis in New Zealand

The introduced Australian brushtail possum (Trichosurus vulpecula) is a maintenance host for bovine tuberculosis (TB) in New Zealand and plays a central role in the TB problem in this country. The TB-possum problem emerged in the late 1960s, and intensive lethal control of possums is now used to reduce densities to low levels over 8 million ha of the country. This review summarises what is currently known about the pathogenesis and epidemiology of TB in possums, and how the disease responds to possum control. TB in possums is a highly lethal disease, with most possums likely to die within 6 months of becoming infected. The mechanisms of transmission between possums remain unclear, but appear to require some form of close contact or proximity. At large geographic scales, TB prevalence in possum populations is usually low (1-5%), but local prevalence can sometimes reach 60%. Intensive, systematic and uniform population control has been highly effective in breaking the TB cycle in possum populations, and where that control has been sustained for many years the prevalence of TB is now zero or near zero. Although some uncertainties remain, local eradication of TB from possums appears to be straightforward, given that TB managers now have the ability to reduce possum numbers to near zero levels and to maintain them at those levels for extended periods where required. We conclude that, although far from complete, the current understanding of TB-possum epidemiology, and the current management strategies and tactics, are sufficient to achieve local, regional, and even national disease eradication from possums in New Zealand.

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.

The role of multiple wildlife hosts in the persistence and spread of bovine tuberculosis in New Zealand

AIM

To explore how the inclusion of multi-host dynamics affects the predicted prevalence of bovine tuberculosis (TB) in possums and other host species following the current best practice for control of TB in large difficult and remote areas, to identify which host species are responsible for changes in predicted prevalence, and whether TB can persist in possum-free host communities.

METHODS

Multi-host TB models were constructed, comprising three host species with density-dependent population growth, density-dependent disease transmission and susceptible and infected classes. Models were parameterised for two case studies of current concern in New Zealand, namely chronic TB persistence in a possum-deer-pig complex in extensive forest, and in a possum-pig-ferret complex in unforested semi-arid shrub and grasslands. Persistence of TB in the face of best practice possum control was evaluated from model simulations, and the contribution of different hosts to persistence of TB was assessed by removing each host species in turn from the simulations. A sensitivity test explored how different parameter values affected modelled persistence of TB.

RESULTS

The forest multi-host model-predicted amplification of TB prevalence due to the presence of pigs. The presence of pigs and/or deer did not jeopardise the success of best practice possum control in eradicating TB from the system, as pigs and deer are effectively end-hosts for TB. Sensitivity analyses indicated these interpretations were robust to uncertainty in model parameter values. The grassland system model predicted that the multi-host species complex could potentially lead to failure of eradication of TB under possum-only control, due to TB persisting in ferret and pig populations in the absence of possum hosts through reciprocal scavenging, resulting in spillback transmission to possums once their populations had started to recover from control.

CONCLUSIONS

With respect to management of TB, for modelled forest habitats, 15 years of effective possum control was predicted to eradicate TB from the possum-deer-pig host community, indicating the current focus on possum-only control is appropriate for such areas. For grassland model systems, TB was predicted to persist in the ferret-pig host complex in the absence of possums, potentially jeopardising the effectiveness of possum-only control programmes. However this outcome depended on the occurrence and rate of pigs acquiring TB from ferrets, which is unknown. Thus some estimation of this transmission parameter is required to enable managers to assess if multi-host disease dynamics are important for their TB control programmes.

The epidemiology of Mycobacterium bovis in wild deer and feral pigs and their roles in the establishment and spread of bovine tuberculosis in New Zealand wildlife

In New Zealand, wild deer and feral pigs are assumed to be spillover hosts for Mycobacterium bovis, and so are not targeted in efforts aimed at locally eradicating bovine tuberculosis (TB) from possums (Trichosurus vulpecula), the main wildlife host. Here we review the epidemiology of TB in deer and pigs, and assess whether New Zealand's TB management programme could be undermined if these species sometimes achieve maintenance host status. In New Zealand, TB prevalences of up to 47% have been recorded in wild deer sympatric with tuberculous possums. Patterns of lesion distribution, age-specific prevalences and behavioural observations suggest that deer become infected mainly through exposure to dead or moribund possums. TB can progress rapidly in some deer (<10%), but generalised disease is uncommon in wild deer; conversely some infected animals can survive for many years. Deer-to-deer transmission of M. bovis is rare, but transmission from tuberculous deer carcasses to scavengers, including possums, is likely. That creates a small spillback risk that could persist for a decade after transmission of new infection to wild deer has been halted. Tuberculosis prevalence in New Zealand feral pigs can reach 100%. Infections in lymph nodes of the head and alimentary tract predominate, indicating that TB is mostly acquired through scavenging tuberculous carrion, particularly possums. Infection is usually well contained, and transmission between pigs is rare. Large reductions in local possum density result in gradual declines (over 10 years) in TB prevalence among sympatric wild deer, and faster declines in feral pigs. Elimination of TB from possums (and livestock) therefore results in eventual disappearance of TB from feral pigs and wild deer. However, the risk of spillback infection from deer to possums substantially extends the time needed to locally eradicate TB from all wildlife (compared to that which would be required to eradicate disease from possums alone), while dispersal or translocation of pigs (e.g. by hunters) creates a risk of long-distance spread of disease. The high rate at which pigs acquire M. bovis infection from dead possums makes them useful as sentinels for detecting TB in wildlife. It is unlikely that wild deer and feral pigs act as maintenance hosts anywhere in New Zealand, because unrestricted year-round hunting keeps densities low, with far less aggregation than on New Zealand farms. We conclude that active management of wild deer or feral pigs is not required for local TB eradication in New Zealand.

Development of integrated surveillance systems for the management of tuberculosis in New Zealand wildlife

Disease surveillance for the management of bovine tuberculosis (TB) in New Zealand has focussed, to a large extent, on the development of tools specific for monitoring Mycobacterium bovis infection in wildlife. Diagnostic techniques have been modified progressively over 30 years of surveillance of TB in wildlife, from initial characterisation of gross TB lesions in a variety of wildlife, through development of sensitive culture techniques to identify viable mycobacteria, to molecular identification of individual M. bovis strains. Of key importance in disease surveillance has been the elucidation of the roles that different wildlife species play in the transmission of infection, specifically defining brushtail possums (Trichosurus vulpecula) as true maintenance hosts compared to those that are predominantly spillover hosts, but which may serve as useful sentinel species to indicate TB persistence. Epidemiological modelling has played a major role in TB surveillance, initially providing the theoretical support for large-scale possum population control and setting targets at which control effort should be deployed to ensure disease eradication. As TB prevalence in livestock and wildlife declined throughout the 2000s, more varied field tools were developed to gather surveillance data from the diminishing possum populations, and to provide information on changing TB prevalence. Accordingly, ever more precise (but disparate) surveillance information began to be integrated into multi-faceted decision-assist models to support TB management decisions, particularly to provide informed parameters at which control effort could be halted, culminating in the Proof of Freedom modelling framework that now allows an area to be declared TB-free within chosen confidence limits. As New Zealand moves from large-scale TB control to regional eradication of disease in the coming years, further integrative models will need to be developed to support management decisions, based on combined field data of possum and TB prevalence, sentinel information, risk assessment in relation to financial benefits, and changing political and environmental needs.

Epidemiology, diagnostics, and management of tuberculosis in domestic cattle and deer in New Zealand in the face of a wildlife reservoir

The control of tuberculosis (TB) in cattle and farmed deer in New Zealand has been greatly influenced by the existence of a wildlife reservoir of Mycobacterium bovis infection, principally the Australian brushtail possum (Trichosurus vulpecula). The reduction in possum numbers in areas with endemic M. bovis infection through vigorous vector control operations has been a major contributor to the marked reduction in the number of infected cattle and farmed deer herds in the past two decades. Management of TB in cattle and farmed deer in New Zealand has involved a combination of vector control, regionalisation of diagnostic testing of cattle and deer herds, abattoir surveillance and movement control from vector risk areas. Accurate diagnosis of infected cattle and deer has been a crucial component in the control programme. As the control programme has evolved, test requirements have changed and new tests have been introduced or test interpretations modified. Subspecific strain typing of M. bovis isolates has proved to be a valuable component in the epidemiological investigation of herd breakdowns to identify whether the source of infection was domestic livestock or wildlife. New initiatives will include the use of improved models for analysing diagnostic test data and characterising disease outbreaks leading to faster elimination of infection from herds. The introduction of the National Animal Identification Tracing programme will allow better risk profiling of individual herds and more reliable tracing of animal movements. TB in cattle and farmed deer in New Zealand can only be controlled by eliminating the disease in both domestic livestock and the wildlife reservoir.

Assessing the Effectiveness of Tuberculosis Management in Brushtail Possums (Trichosurus vulpecula), through Indirect Surveillance of Mycobacterium bovis Infection Using Released Sentinel Pigs

In New Zealand, wild pigs acquire Mycobacterium bovis infection by scavenging tuberculous carrion, primarily carcasses of the main disease maintenance host, the brushtail possum (Trichosurus vulpecula). We investigated the utility of captive-reared, purpose-released pigs as sentinels for tuberculosis (TB) following lethal possum control and subsequent population recovery. Within 2-3 years of possum control by intensive poisoning, TB prevalence and the incidence rate of M. bovis infection in released sentinel pigs were lower than in an adjacent area where possums had not been poisoned. Unexpectedly, TB did not decline to near zero levels among pigs in the poisoned area, a fact which reflected an unanticipated rapid increase in the apparent abundance of possums. Monitoring infection levels among resident wild pigs confirmed that TB prevalence, while reduced due to possum control, persisted in the poisoned area at >20% among pigs born 2-3 years after poisoning, while remaining >60% among resident wild pigs in the nonpoisoned area. When fitted with radio-tracking devices, purpose-released pigs provided precise spatial TB surveillance information and facilitated effective killing of wild pigs when employed as “Judas” animals to help locate residents. Sentinel pigs offer value for monitoring disease trends in New Zealand, as TB levels in possums decline nationally due to large-scale possum control.

Evaluating the tuberculosis hazard posed to cattle from wildlife across Europe

Tuberculosis (TB) caused by infection with Mycobacterium bovis (M. bovis) and other closely related members of the M. tuberculosis complex (MTC) infects many domestic and wildlife species across Europe. Transmission from wildlife species to cattle complicates the control of disease in cattle. By determining the level of TB hazard for which a given wildlife species is responsible, the potential for transmission to the cattle population can be evaluated. We undertook a quantitative review of TB hazard across Europe on a country-by-country basis for cattle and five widely-distributed wildlife species. Cattle posed the greatest current and potential TB hazard other cattle for the majority of countries in Europe. Wild boar posed the greatest hazard of all the wildlife species, indicating that wild boar have the greatest ability to transmit the disease to cattle. The most common host systems for TB hazards in Europe are the cattle-deer-wild boar ones. The cattle-roe deer-wild boar system is found in 10 countries, and the cattle-red deer-wild boar system is found in five countries. The dominance of cattle with respect to the hazards in many regions confirms that intensive surveillance of cattle for TB should play an important role in any TB control programme. The significant contribution that wildlife can make to the TB hazard to cattle is also of concern, given current population and distribution increases of some susceptible wildlife species, especially wild boar and deer, and the paucity of wildlife TB surveillance programmes.

Importance and mitigation of the risk of spillback transmission of Mycobacterium bovis infection for eradication of bovine tuberculosis from wildlife in New Zealand

Introduced brushtail possums (Trichosurus vulpecula) are wildlife maintenance hosts for Mycobacterium bovis in New Zealand, often living sympatrically with other potential hosts, including wild red deer (Cervus elaphus scoticus). Population control of possums has been predicted to eradicate tuberculosis (TB) from New Zealand wildlife; however, there is concern that long-lived M. bovis-infected deer could represent a ‘spillback’ risk for TB re-establishment (particularly when possum populations recover after cessation of intensive control). We constructed a time-, age- and sex-structured, deer/TB population generic model and simulated the outcomes of deer control on this potential spillback risk. Maintaining intensive possum control on a 5-year cycle, the predicted spillback risk period after TB eradication from possums is ∼7 years, while the probability of TB re-establishing in possums over that period is ∼6%. Additional targeted control of deer would reduce the risk period and probability of spillback; however, even with high population reductions (up to 80%) only modest decreases in risk and risk period would be achieved. We conclude that possum control alone remains the best strategy for achieving TB eradication from New Zealand habitats in which possums and wild deer are the main M. bovis hosts.

Progress in Oral Vaccination against Tuberculosis in Its Main Wildlife Reservoir in Iberia, the Eurasian Wild Boar

Eurasian wild boar (Sus scrofa) is the main wildlife reservoir for tuberculosis (TB) in Iberia. This review summarizes the current knowledge on wild boar vaccination including aspects of bait design, delivery and field deployment success; wild boar response to vaccination with Bacillus Calmette-Guérin (BCG) and inactivated Mycobacterium bovis; and wild boar vaccination biosafety issues as well as prospects on future research. Oral vaccination with BCG in captive wild boar has shown to be safe with significant levels of protection against challenge with virulent M. bovis. An oral vaccination with a new heat-killed M. bovis vaccine conferred a protection similar to BCG. The study of host-pathogen interactions identified biomarkers of resistance/susceptibility to tuberculosis in wild boar such as complement component 3 (C3) and methylmalonyl coenzyme A mutase (MUT) that were used for vaccine development. Finally, specific delivery systems were developed for bait-containing vaccines to target different age groups. Ongoing research includes laboratory experiments combining live and heat-killed vaccines and the first field trial for TB control in wild boar.

Mycobacterium bovis: A Model Pathogen at the Interface of Livestock, Wildlife, and Humans

Complex and dynamic interactions involving domestic animals, wildlife, and humans create environments favorable to the emergence of new diseases, or reemergence of diseases in new host species. Today, reservoirs of Mycobacterium bovis, the causative agent of tuberculosis in animals, and sometimes humans, exist in a range of countries and wild animal populations. Free-ranging populations of white-tailed deer in the US, brushtail possum in New Zealand, badger in the Republic of Ireland and the United Kingdom, and wild boar in Spain exemplify established reservoirs of M. bovis. Establishment of these reservoirs is the result of factors such as spillover from livestock, translocation of wildlife, supplemental feeding of wildlife, and wildlife population densities beyond normal habitat carrying capacities. As many countries attempt to eradicate M. bovis from livestock, efforts are impeded by spillback from wildlife reservoirs. It will not be possible to eradicate this important zoonosis from livestock unless transmission between wildlife and domestic animals is halted. Such an endeavor will require a collaborative effort between agricultural, wildlife, environmental, and political interests.

Epidemiological significance of the domestic black pig (Sus scrofa) in maintenance of bovine tuberculosis in Sicily

Bovine tuberculosis (bTB) is an emerging disease among wild animals in many parts of the world. Wildlife reservoir hosts may thus represent a potential source of infection for livestock and humans. We investigated the role played by the Sicilian black pig, an autochthonous free- or semi-free-ranging domestic pig breed, as a potential source of bTB infection in an area where bTB prevalence in cattle is high. We initially performed a preliminary field study to assess the occurrence of bTB in such animals. We sampled 119 pigs at abattoir and found 6.7% and 3.4% of them to be affected by gross tuberculous-like lesions (TBL) and Mycobacterium bovis culture positive, respectively. We then proceeded to investigate the dissemination and characteristics of lesions in a second field study performed on 100 animals sampled from infected herds. Here, tissues collected at the abattoir were examined macroscopically, microscopically, and by culture tests. Most pigs with TBL showed generalized lesions in both gross and histological examinations (53% and 65.5%, respectively). Head lymph nodes were the most frequently affected in both localized and generalized TB cases observed macroscopically and microscopically. M. bovis was the most frequently isolated etiologic agent. The molecular characterization of isolates from both field studies by spoligotyping and analysis of 12 mycobacterial interspersed repetitive-unit-variable number tandem repeat (MIRU-VNTR) loci, followed by their comparison to isolates of cattle origin, suggested a potential transmission of mycobacteria from domestic animals to black pigs and vice versa. Our findings, along with ethological, ecological, and management considerations, suggest that the black pig might act as a bTB reservoir in the ecosystem under study. However, additional studies will be necessary to establish the true epidemiological significance of the Sicilian black pig.