Variation in the immune response of badgers and the diagnosis of bovine tuberculosis

Abstract

Diagnosing diseases in wildlife is challenging, the availability of diagnostic tests that perform at the same level of sensitivity and specificity in wild animals as their human and livestock counterparts is limited. In the last few decades increased awareness of the role of wild animals in the maintenance and spread of important zoonotic infections means that research has been directed into development of specific diagnostic tests aimed at wildlife that can be used for research, surveillance and wildlife control programmes. Wild animals are subject to a wide range of genetic and environmental factors many of which may influence their immune response. These additional pressures may affect the immune system in different ways and within a group of animals; individuals will vary. The first aim of this dissertation was to investigate variation in the cell-mediated immune (CMI) response of free-living badgers to a range of intrinsic factors. Results revealed factors that may suppress the non-specific immune response such as old age, presence of wounds and larger social group sizes and those that amplify the specific M. bovis response such as age, presence of wounds and bTB exposure. Results also showed complex interactions between body condition with age, sex and season which influenced both the specific and non-specific CMI response. Second, to aid in disease surveillance and management, we developed and evaluated a technique to collect and test blood from unanaesthetised badgers in the field. This study successfully demonstrated proof of concept where a method of capillary blood collection used in the field enabled the operator to carry out a rapid diagnostic test for the presence of Mycobacterium bovis infection. In addition we have shown that the accuracy of the DPP VetTB test carried out in the controlled conditions of the laboratory cannot be replicated when testing under field conditions suggesting that stochastic conditions in the field may affect TB diagnostic outcomes. My findings illustrate the importance of understanding variation in test performance, arising from intrinsic and extrinsic factors in diagnosing and managing bovine tuberculosis in badgers, and other diseases of highly variable wild hosts.