Resumen de Tuberculosis in wild boar and red deer: diagnosis and control in intensive management systems
Animal tuberculosis (TB) is one of the infectious diseases of livestock and wildlife of more concern, worldwide. This is due to its huge impact on aspects such as public health, economy, wildlife management and conservation. The purpose of the thesis is to provide information on the implementation of practical and accessible TB diagnostic tests in two wild ungulates, wild boar and red deer, using these tools as control strategies for TB in wild animals. In addition, we aimed to study the role played by other infections in wild boar piglet mortality.
The thesis is composed of an introductory main overview section and four research chapters, each of them dealing with specific studies on different ante-mortem tests, a field TB control trial based on targeted culling, and a disease investigation in wild boar under intensive management.
Chapter one is a general overview of TB and defines basic terminology. It also details the information and knowledge related to the research of the thesis. Chapter one is subdivided into two parts. Part one describes the state of the art regarding TB diagnosis in wildlife, TB hazard related issues among animals and humans, economy and conservation. It also comprehensively describes the current diagnostic tests for MTC that have been studied or used in wildlife species globally. Part two deals with specific reviews on the current knowledge on global TB distribution and the significance of wildlife hosts; recognizes insufficiently known aspects of host pathology, ecology and epidemiology; presents selected time series in wildlife TB; and summarizes ongoing research on TB control, providing additional insight on vaccination.
Chapter two assesses the performance of several antibody detection tests for M. bovis infection in free-living, naturally-exposed 2–6 month-old piglets during summer. This cross sectional study included necropsies with macroscopic identification of TB-like lesions, Mycobacterium tuberculosis complex (MTC) bacterial culture and identification, and six different serological antibody tests. A total of 126 samples of wild boar piglets which died within summer in 2012 and 2013 were incorporated in the analysis. Bacterial culture yielded a prevalence of 33.9%, while prevalences estimated by serology ranged from 19.0 to 38.0%, achieving the best sensitivities between 61.5% and 69.2% for rapid immunochromatographic tests based on the dual path platform (DPP) technology as compared the other four plate ELISAs. This chapter evidences that about 33% of the wild boar piglets can become infected at early age in high TB prevalence sites. Serology able to detect antibodies against MTC in piglets however is rather less sensitive than in adult wild boar. Rapid animal-side tests can contribute to TB control using test and cull schemes.
Chapter three addresses the question whether repeated skin testing with avian and bovine purified protein derivative (aPPD, bPPD), for instance every 6 months,could affect the skin test responsiveness or the antibody levels against mycobacterial antigens in TB-free red deer. This question arises since the tuberculin skin test is the routinely used one for TB diagnosis in ruminant species, including wild animals. We observed that repeated comparative skin testing did not cause progressive changes or specifically cause a loss in skin test responsiveness against bPPD tuberculin or in ELISA antibody responses against bPPD and MPB70 antigens. However, the results showed ELISA antibody increases through times against avian PPD and PPA3 antigens, which possibly were due to exposure to Mycobacterium avium paratuberculosis (MAP) or to cross reactions with environmental mycobacteria. Thus, this diagnostic method can be applied for the TB control programme without the fear for progressive sensitization or de-sensitization.
Chapter four focuses on one specific control strategy to reduce TB transmission between wildlife and livestock, namely targeted culling of infected wildlife. The main aim of the research reported in this chapter was to reduce the TB prevalence in the control site by implementing a targeted removal strategy, i.e. by selectively removing seropositive wild boar (using immunochromatographic DPP rapid tests) from one hunting estate and harvesting them by hunting on the release site. This capture-test-release trial was conducted in summer 2012-2014. The annual summer seroprevalence of antibodies to the MTC declined significantly by 39% in live-captured wild boar piglets from the treatment site, from 2012 to 2013 with no further reduction during the third capture season. Adversely, the MTC prevalence in the release site increased significantly by 60% in the hunter-harvested population. Targeted removal attempted in this TB control strategy within a high infection pressure area failed to reduce the prevalence, nevertheless generating valuable knowledge on this specific TB control tool and on TB epidemiology at very high force of infection.
Finally, in the site with high force of infection, we led a cross sectional investigation to elucidate the causes for a marked mortality among wild boar piglets during summer. The findings were, that the expected piglet mortality during summer 2015 was extremely high (71%) as measured by the decrease of the piglet-to-adult ratio at the feeders through video-trapping analysis, as well as by interviewing the game rangers. In addition to that, dead piglets aged less than 4-month-old have indicated poor body condition, 88.9% had PRDC-compatible respiratory lesions predominantly characterized by pneumonia, and Porcine Circovirus Type 2 (PCV2) was the most prevalent single pathogen at 39%. However, no clear relationship between prevalence and lung lesions was observed for the PRDC associated pathogens (PCV2, Mycoplasma hyopneumoniae), nor for MTC infection. Respiratory infection characterized by pneumonia, but not MTC infection per se, was the most plausible reason of the high mortality recorded among early age wild boar piglets.
