The COVID-19 pandemic once again confirmed that zoonotic diseases are a serious threat to humanity. These infectious diseases, transmitted from animals to humans, have the power to cause a global health crisis. Over time the risk on these outbreaks has increased. Some of the main drivers are global population growth, urbanization, worldwide transport, increased demand for animal protein, unsustainable agriculture, and climate change. This development has fueled a renewed interest in the relation between human, animal and environmental health. This was (...) framed in the concept of One Health: the integrative effort of multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment. At present, One Health is the worldwide standard to combat zoonotic diseases. In an ideal world such a strategy should lead to a better health for humans, animals and our environment. However, in practice it is not self-evident that a One Health approach in zoonotic disease control is actually in the interest of animals or the environment. From a holistic One Health perspective it can be difficult to accept the culling of healthy animals to protect public health. The same goes for long term confinement of free-range poultry, whose housing systems are often not suitable for this purpose, to prevent avian influenza outbreaks. Or antimicrobial reduction policies that lead to higher disease incidence and mortality in animals. These ethical considerations formed the start of this thesis. The aim of my research is to clarify the ethical assumptions of a One Health approach in zoonotic disease control, to explore how these can be coherently understood and justified and to indicate what this implies for policymaking. The outcome of my research contributes to the development of an ethic of One Health and will hopefully lead to a more socially acceptable zoonotic disease control. This project is related to the interdisciplinary Wageningen UR strategic research theme ‘Global One Health’. From my conceptual analysis, it follows that there is no universal interpretation of the One Health concept nor of a One Health approach in zoonotic disease control. Nevertheless, One Health has produced several successes in zoonotic disease control, surveillance and research. Due to its ambiguity, the One Health concept functions as a boundary object: by leaving room for interpretation to fit different purposes it facilitates cooperation. In many cases this results in the promotion of health of humans, animals and the environment. However, there are also situations in which this mutual benefit of a One Health approach is not that evident. For instance, when healthy animals are culled to protect public health. To address these moral dilemmas, it is important to develop an ethical framework. Such an ethic of One Health starts with acknowledging the moral status of animals and the indirect moral obligations we have towards ecosystems. Furthermore, it is necessary that we find an appropriate definition of health, which encompasses all three components of One Health. In chapter 3, I present the results of an empirical study on normative presuppositions of health professionals involved in zoonotic disease control policies in the Netherlands. This study reveals that in theory these professionals adhere to a holistic view of the One Health concept. However, in practice an anthropocentric approach was dominant. The study identified public health as a trumping moral value, which reveals an inherent field of tension with the core of One Health thinking. Furthermore, a lack of ethical expertise in control systems for zoonotic diseases can lead to misconception of ethical principles, like the precautionary principle. In chapter 4, I discuss that within a One Health strategy, that requires us to balance public health benefits against the health interests of animals and the environment, unrestricted use of the precautionary principle can lead to moral dilemmas. It must at least be clear that there is a harm and some scientific evidence for a cause and effect relation. Furthermore, precautionary measures should be effective, consistent, proportional and not counterproductive. An assessment of their effect should be integrated in the standard decision-models of public health authorities. Moreover, to ensure societal support these considerations should be transparent and open for dialogue. I present two possible conceptions of the precautionary principle. First, it is noticeable that because of the unpredictable nature of zoonotic diseases, public health authorities focus on the idea of ‘precaution as preparedness’. This reactive response leads to difficult trade-offs between human and animal health. I therefore argue that this policy should always be accompanied by a second policy: ‘precaution as prevention’. Addressing the underlying drivers of zoonotic diseases is a necessary condition to justify disease control measures that harm animals and ecosystems on the basis of the precautionary principle. In chapter 5, I elaborate the responsibilities of veterinarians within the One Health framework. Veterinarians are professionally responsible for the health and welfare of the animals under their care. Moreover, society expects veterinarians to safeguard food safety and public health. These societal expectations are sometimes overdemanding. A holistic perspective on One Health offers veterinarians a way out of the dichotomy between public and animal health, that is at the basis of many moral dilemmas in zoonotic disease control. This is explained with the ‘encapsulated health’ argument: the best way to safeguard human health is to promote the health of animals and the environment. In chapter 6, I conclude that before we decide to implement certain disease control measures, an ethic of One Health requires that we choose those interventions that have the least impact on the health of animals and ecosystems, while still effective enough to stop the disease. My research indicates that the contemporary conception of One Health is necessary but insufficient to address moral dilemmas related to emerging zoonotic diseases. A holistic interpretation of the One Health concept confronts us with underlying value conflicts but will ultimately promote human health more than the current anthropocentric conception. (shrink)