Sustained protection against tuberculosis conferred to a wildlife host by single dose oral vaccination
ABSTRACT BACKGROUND: Vaccination of wildlife against bovine tuberculosis (TB) is being considered by several countries to reduce the transmission of Mycobacterium bovis infection to livestock. In New Zealand, where introduced brushtail possums (Trichosurus vulpecula) are the major wildlife hosts, we have previously shown that repeat applications of a lipid-encapsulated oral bacille Calmette-Guerin (BCG) vaccine reduce the incidence of naturally acquired TB in wild possums. Here we extend this conceptual demonstration to an operational level, assessing long-term protection against TB conferred to free-living possums by a single oral immunisation. METHODS: Possums in a non-TB area were randomly allocated to receive lipid-formulated BCG vaccine or remained unvaccinated. After initial trials to assess vaccine immunogenicity and establishment of protection within the first year post-vaccination, 13 individuals of each treatment group were relocated to a biosecurity facility and challenged (at 28 months post-vaccination) by subcutaneous injection of virulent M. bovis. RESULTS: Vaccine immunogenicity and short-term protection were confirmed at 2 months and 12 months post-vaccination, respectively. In the long-term assessment, vaccinated possums had significantly reduced bacterial counts in peripheral lymph nodes compared to controls, with 0.6-2.3 log(10)-fold reductions in M. bovis burdens. DISCUSSION: The magnitude of protective response by possums to experimental challenge at 28 months post-vaccination is known to equate to a high degree of protection against natural infection in this species. With techniques for oral bait delivery well advanced, the longevity of protection demonstrated here shows that an operable wildlife vaccine against TB is feasible.
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ABSTRACT: Context. Bovine tuberculosis is a persistent disease of livestock in many parts of the world, especially where wildlife hosts co-exist with livestock. In south-western Spain, despite the widespread implementation of test-and-cull strategies for cattle, the herd prevalence in areas with high wild boar densities remains stable. The control of M. bovis infection in wild boar is likely to be essential for effective disease control in livestock. Methods. We developed an individual-based model to evaluate whether vaccinating wild boar piglets with oral bait would be an effective strategy to reduce the prevalence of M. bovis infection in wild boar populations. Specifically, we quantified the proportion of piglets requiring vaccination and the number of years the vaccination programme would need to continue to eradicate bTB from wild boar within 25 years, comparing 'managed' populations on hunting estates where supplementary food is provided, with 'unmanaged', free-living populations. Successful vaccination was defined as the proportion of piglets that were delivered the vaccine and were effectively protected from infection. Key results. Longer-term (25-year) vaccination strategies were more successful than short-term (5-year) strategies at either eradicating M. bovis or reducing it to below 90% of its original prevalence. M. bovis infection could be eradicated under a 25-year vaccination strategy if 80% of piglets were vaccinated in a managed population or 70% of piglets were vaccinated in an unmanaged population. In contrast, 5-year strategies in which 80% of piglets were vaccinated reduced the prevalence of M. bovis only by 27% or 8% in the managed and unmanaged populations, respectively. Conclusions. The results of our simulation model, coupled with the promising results of initial vaccine and oral bait-uptake trials in wild boar indicated that vaccination could be an effective strategy to reduce the prevalence of M. bovis infection in wild boar if used in conjunction with other disease-control measures. Implications. The vaccination of piglets over a long-term period has the potential to make an important contribution to the eradication of M. bovis infection from wild boar reservoirs in southern Spain.CSIRO Wildlife Research 01/2013; 40(5). DOI:10.1071/WR12139 · 1.19 Impact Factor
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ABSTRACT: White-tailed deer (Odocoileus virginianus) in Michigan, USA, are wildlife reservoirs of bovine tuberculosis (bTB) with documented spread to cattle. In vaccine efficacy trials, Mycobacterium bovis bacillus Calmette–Guerin (BCG) administered orally reduces colonization and bTB-associated lesions in white-tailed deer after experimental challenge with virulent M. bovis. The objective of this study was to develop and evaluate the palatability of a molasses-based bait for oral delivery of BCG to white-tailed deer. Relevant practical properties of the bait such as physical stability under various environmental conditions were evaluated, as well as palatability. Captive deer consumed baits within 3 h of introduction during 48 of 50 trials. Digital game cameras revealed consumption of all placed baits by one deer over 62 % of the time. Addition of BCG vaccine did not negatively impact palatability. Physical stability analysis demonstrated that ice and water significantly reduced bait stability as measured with a compression assay. Storage of BCG-containing baits at 4 °C showed a slight decrease in colony-forming units (CFUs) by day 31. In contrast, storage at −20 or −80 °C over the same 31-day period showed no significant decrease in BCG viability. The results of this study suggest that molasses-based baits, as prepared here, represent a plausible means of oral delivery of BCG to white-tailed deer under most environmental conditions.European Journal of Wildlife Research 04/2014; 60(2). DOI:10.1007/s10344-013-0777-9 · 1.21 Impact Factor
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ABSTRACT: Wildlife disease has the potential to cause significant ecological, socioeconomic, and health impacts. As a result, all tools available need to be employed when host–pathogen dynamics merit conservation or management interventions. Evolutionary principles, such as evolutionary history, phenotypic and genetic variation, and selection, have the potential to unravel many of the complex ecological realities of infectious disease in the wild. Despite this, their application to wildlife disease ecology and management remains in its infancy. In this article, we outline the impetus behind applying evolutionary principles to disease ecology and management issues in the wild. We then introduce articles from this special issue on Evolutionary Perspectives on Wildlife Disease: Concepts and Applications, outlining how each is exemplar of a practical wildlife disease challenge that can be enlightened by applied evolution. Ultimately, we aim to bring new insights to wildlife disease ecology and its management using tools and techniques commonly employed in evolutionary ecology.Evolutionary Applications 08/2014; 7(7). DOI:10.1111/eva.12179 · 4.57 Impact Factor