(e.g. politicians, non-governmental organizations (NGOs)) and practitioners is needed in One Health.
The added value from inter- and transdisciplinary science has also been addressed in other studies. Manlove et al. (2016) found in a literature survey that many of the One Health publications could be clustered in three different silos and although more overlap between the silos occurred through time, this was still the case. In order to benefit inter- and transdisciplinary science, crucial for One Health, Rüegg et al. (2018) created a One Health index (OHI) to evaluate whether research is One Health or only focused on one discipline. The authors suggest that it might be less beneficial if the OHI is too high or too low, but the optimal range of the OHI index is still unclear. That could be used either to visualize how to make research more inter- or transdisciplinary, to show how the index changes over time, or as a tool to use in the distribution of funding.
Fig. 5.1 attempts to illustrate a Boolean depiction of the different terms and concepts relevant to different One Health approaches. One Health is at the intersection of human (public) health and animal health. Global health extends public health to an international level but does not include animal health. Ecosystem approaches to health (ecohealth) have a stronger emphasis on ecology and more sciences from the arts and humanities are included and thus clearly encompass One Health (Lerner and Berg, 2017). Planetary health is more anthropocentric and attempts to relate health with global change phenomena such as climate change (Lerner and Berg, 2017). This has also been found in a scientometric analysis of scientific papers within the field of planetary health (Falceto de Barros et al., 2019).
Fig. 5.1. Boolean depiction of health concepts and approaches to health. All these terms and concepts are relevant to One Health approaches. Green, animal health; red, human (public) health; yellow, global health; black, ecosystem approaches to health (ecohealth) or health in social-ecological systems (HSES); blue, planetary health.
The Demarcation of ‘Health’ in One Health
The concept of health is crucial to define for the One Health approach. To promote health, one needs to have a clear idea of what kind of health one aims for. Policy work as well as how to allocate resources are dependent on what is included in health. However, there is a lack of theoretical discussion on how to define the concept within the One Health approaches. Health is much more complicated in One Health approaches than, for example, in global health, where only human health is considered. In One Health approaches, at the least both human and animal health need to be considered (Lerner and Berg, 2015, 2017). There are also claims that plant health should be included in the considerations (Fletcher et al., 2009). Also important is to consider how many aspects of life need to be covered. Should the definition apply only to physical aspects or also to mental, social and even spiritual aspects?
Health could also be considered on different levels, such as individual, population and ecosystem levels of health (Lerner and Berg, 2015). The first two are familiar to the disciplines of human and veterinary medicine and public health, but the third level, ecosystem health, is seldom recognized, and this makes One Health a more holistic transdisciplinary approach. In order to work with ecosystem health, biologists, environmentalists and others must be included in the approach. Sometimes, as in the One Health Commission and the One Health Initiative definitions, the term ‘environmental’ is used in the same manner as ‘ecosystem’.
There are claims that the concept of health should be clearly defined for at least animals and humans (Stephen, 2014). Could there be a universal definition of health for, at least, both animals and humans? This might imply that the definition of health should be non-speciesist. In order to reach such a definition, one can follow two routes, either start from a human concept of health (top-down) and widen it to include animals, or one can find a common basic level for animals and humans (bottom-up) and define this as health. The first route might be too anthropocentric as well as not including enough species. The second route might be too basic for all aspects of human, and some species of animal, health (Lerner, 2019).
To define health bottom-up one starts by finding a common denominator. Mainly, these definitions are based on biology. A pioneer of One Health approaches, Rudolf Virchow, who defined health in terms of vital cells is an example of this. In Virchow’s definition, health is considered present when enough cells are vital (Virchow, 1881). Species in all biological kingdoms consist of cells, and the definition of health could therefore easily be applied to all organisms. A more modern bottom-up version of health is Christopher Boorse’s biostatistical theory of health, where health is regarded as species-specific functioning of biological organs (Boorse, 1997).
Top-down health definitions, on the other hand, start with definitions of human health and are expanded to other species if they share characteristics that are the foundation of these particular health definitions. These definitions are more holistic and encompass physical, mental and social aspects of an individual. An example of this is the WHO definition of health, covering physical, mental and social aspects of well-being. Nowadays, this definition has expanded to cover mammals and birds, at least in some fields of veterinary medicine (Lerner, 2017).
Is it possible to have a universal concept of health for all levels? A couple of aspects make this difficult. One should decide whether health should be defined as a state or as a process. Both ways exist. Health at the individual level is often defined as a state (Nordenfelt, 2006), while processes might be more important at population and ecosystem level. There might also be potential conflicts between these three levels. This is a similar problem as in ethics when individuals are compared to species or to ecosystems. Where should health apply? In the individual or outside the individual at an aggregated level such as the individual’s population or the individual’s ecosystem? In ethics, simplified, this question created the divide between animal ethics and environmental ethics (Lerner and Berg, 2015). Here, further discussions are needed.
There are many definitions of health present, and no consensus exists on what definition to choose. Recently, a thorough analysis of the idea that health should be a kind of balance was performed with a One Health perspective (Lerner, 2019). This study analysed which definitions based on an idea of balance could be suitable for One Health. Both bottom-up and top-down definitions were analysed. The conclusion was that there were promising aspects with some definitions, but there were also obstacles that made current definitions not fully applicable in One Health without some adjustments.
Despite the problems there are also other fruitful attempts to find universal non-speciesist definitions of health (Lerner, 2017). Lerner (2019)
