Control mediante vacunación de la tuberculosis en su principal reservorio silvestre en españa, el jabalí

Abstract

The control of diseases shared with wildlife requires the development of strategies that will reduce pathogen transmission between wildlife and both domestic animals and human beings. Disease control can be achieved by different means, including: (1) preventive actions, (2) arthropod vector control, (3) host population control, habitat management or reproductive control, and (4) vaccination. The present thesis approaches control options of shared diseases where wildlife plays a significant role in maintenance using the control of animal tuberculosis (TB) in wild boar (Sus scrofa) by vaccination as a case study. TB has an impact over Public Health, economy and wildlife management and conservation. TB is also the perfect example of a shared disease as these pathogens are capable to infect and produce disease in multiple animal species, domestic and wild, including humans. In particular, the role of wildlife reservoirs in TB maintenance is increasingly acknowledged worldwide. In Spain, wild boar is recognized as the main wild reservoir. Vaccination is perceived as a feasible disease control option for cost effective and long-term TB control in wildlife. Wildlife vaccination goal is to control rather than eradicate disease and prioritizes population over individuals ultimately aiming to reduce disease burden and spread of infection at the population level in targeted and sympatric species. The only licensed vaccine against TB is Bacille Calmette–Guérin (BCG). Despite being the only commercial option, it does not provide sterilizing immunity and has variable efficacy in humans and animals. Hence, the continued search of new vaccine candidates (more protective or suitable for field use as the recently developed heat-inactivated M. bovis, IV) and alternative immunization strategies (such as heterologous protocols). The main objectives of this thesis were to evaluate the impact attained by vaccination and feasibility of this measure in real-life settings and to explore in the laboratory vaccine combinations that provide enhanced protection. These objectives were addressed in: Chapter I: Assessment of safety and efficacy of parenteral IV candidate in a wild boar farm under natural TB transmission Chapter II: Compare the impact of two vaccines (BCG and IV) in free-ranging wild boar populations (managed and not) under natural TB transmission and the feasibility of vaccinating large areas. Questions that could not be tested in field such as exploring the influence of vaccination success gradients, the effect of long-term vaccination and vaccination cessation on population and disease dynamics under different initial prevalence/transmission scenarios were answered by mathematical models. Chapter III: To test BCG and IV combinations (heterologous vaccination) under controlled laboratory conditions in order to improve vaccine efficacy. The conclusions arising from these works are: Chapter I: Parenteral vaccination with IV is safe and protects farmed wild boar, and eventually pigs, from disease (66% TB reduction). Chapter II: Oral vaccination via baits in free-ranging wild boar piglets is feasible and resulted in the vaccination of more than 70% of wild boar piglets. Oral vaccination with BCG under field conditions did not lead to significant reductions in TB disease prevalence. Oral vaccination with IV under field conditions resulted in a significant reduction of TB prevalence after four years of vaccine deployment only in the population belonging to the managed site (34% decrease). Long-term vaccination would be able to control but not to eradicate disease and will have an impact over population dynamics (increased abundance via decreased mortality) according to modeling results. Vaccine success is greater if applied over well-defined populations (farmed or managed), with low to moderate prevalence (10 to 50%) and targeting a large proportion of the population. Chapter III: Heterologous vaccination regimes involving BCG and IV do not provide improved protection in the wild boar model as compared to homologous regimes. Homologous regimes are the best option for vaccination of wild boar and pigs against TB. Moreover, vaccine sequence dramatically influenced the outcome underlining the relevance of studying the effects of sensitization in the outcome of vaccination Vaccination is a realistic option to contain TB in wild boar, ideally as part of an integrated control strategy that combines several tools, targets all the epidemiologically relevant hosts and involves all the interested stakeholders.