Tuberculosis in wildlifenew diagnostic tests and host response to vaccination in red deer

Résumé

Animal Tuberculosis (TB) is a chronic infectious disease, which represents a major health problem in domestic wild animals as well as in humans. The control and management of TB is an actively ongoing research subject because of its impact on economy, sanitary standards and public health. Moreover, it is recently considered as an emerging threat for conservation. New approaches to diagnosis of TB, especially in wildlife, are gaining relevance in recent years because it is a paramount step for epidemiological investigation, as well as to ensure the success of control strategies. In addition, TB control is more likely to be achieved by an integration of many strategies, including vaccination. However, there is a paucity of information with respect to the efficacy of vaccines like M. bovis heat-inactivated vaccine (IV) in cervids, which has proven not to interfere with the available diagnostic tests. So, considering all these points, our study was designed with the objective to validate new cellular and antibody-mediated diagnostic tests for TB in wildlife ruminants and swine, as well as to assess the effect of oral vaccination with IV in red deer in an experimental challenge study. The thesis comprises an introduction regarding the overview of TB and three chapters, dealing with new diagnostic approaches and an experimental vaccination study for the control of TB in wildlife, followed by a general discussion and conclusion. Chapter 1 deals with development and validation of an interferon gamma assay (IGRA) with different mycobacterial antigens in red deer. This IGRA yielded detection levels up to 100% of the positive and negative deer under experimental conditions; however, the Se of the assay got decreased towards the later stages of the disease. This technique will aid in TB testing of farmed and translocated deer, however, it has yet to be validated in field conditions.Antibody-based diagnosis is a powerful, cost effective and rapid tool for ante-mortem and post-mortem TB diagnosis and large-scale surveillance, especially with regard to swine. Chapter 2 addresses the use of P22, a new immunopurified protein complex derived from bPPD, in M. tuberculosis complex-specific antibodies diagnosis to improve the specificity (Sp) of TB serodiagnostic tests in wildlife. The validation of P22 in an in-house ELISA has been performed in red deer (chapter 2.1) and swine (chapter 2.2) in comparison to the commonly used bPPD ELISA. In red deer, we observed a high Sp (99%) in the P22 ELISA without compromising the sensitivity (Se) (70.1%) compared to bPPD ELISA (Sp - 91.6%, Se - 70.1%) In swine, both ELISAs yielded a good diagnostic value, however, a higher Se and Sp was achieved with the P22 ELISA (Se - 84.1%, Sp - 98.4%) when compared to the bPPD ELISA (Se - 77.3%, Sp - 97.3%). An optimum Sp of 100% was attained with white pigs (reared under intensive management systems) for both the bPPD and P22 ELISA. These findings indicate that specific or purified antigens, especially P22, could contribute to improved performance of TB diagnosis in multiple wildlife hosts, as it occurs in cervids and swine. Deer species are often part of the Mycobacterium tuberculosis complex maintenance host community, and TB control in deer, including vaccination, is consequently an area of ongoing research. Chapter 3 focuses on the efficacy of the oral M. bovis heat-inactivated vaccine in red deer in an experimental challenge model in comparison with oral conventional BCG vaccine. The results suggest that oral M. bovis heat-inactivated vaccine produced a significant reduction in infection burden with respect to the control group. Moreover, by this vaccine delivery route there was no interference with diagnostic tests due to vaccination. This thesis provides new insights to fight against TB in wildlife, improving TB diagnosis and contributing with valuable information about the use of M. bovis heat-inactivated vaccine as a potential candidate vaccine to aid the existing TB control strategies.