interface. For example, elimination of fox rabies in Europe reduced rabies risk to humans and domestic animals (Freuling et al., 2013). On-farm biosecurity for poultry premises will continue to be important to prevent avian influenza transmission between wild birds and poultry (Lee et al., 2018). Efforts to prevent human diseases spilling into wildlife have also been important for maintaining endangered great ape (Hominidae) populations (Gilardi et al., 2017).
Despite its importance, prevention and control of infectious disease will not be sufficient to combat the myriad health effects caused by global forces such as climate change and loss of biodiversity and ecosystem integrity. A health-centric perspective acknowledges the importance of disease as one factor among many that influence the health of humans and animals (see Box 3.1). Scientists often gravitate towards reductionist approaches because observing a single component (e.g. disease) is simpler than trying to observe the entire system. However, the health effects of current One Health challenges, such as climate change loss of ecosystem function, will exceed the impacts of their effects on disease emergence and spread. The complexity of these issues will likely require a systems approach (Zinsstag et al., Chapter 2, this volume) to identify the multitude of drivers (including human values), their interrelationships and feedback loops, so that effective solutions and policy changes can be found (Table 3.1) (Zinsstag et al., 2011).
Table 3.1. Depending on the type of health-related issue, different approaches may be needed to address them. With a disease-centric approach the goal is often disease prevention or mitigation. Systems-oriented health-centric approaches focus on solutions that promote health for which disease prevention or mitigation is only one component. This table illustrates One Health issues associated with either a disease- or health-centric approach.
| Disease-centric approach | Health-centric approach |
|---|---|
| Pathogen spillover and spillback dynamics | Landscape change and habitat fragmentation |
| Prevention of diseases | Securing needs for daily living (e.g. food and water security) (Gordon et al., Chapter 25, this volume) |
| Eradication of pathogens | Climate and environmental change (Zinsstag et al., 2018; Stephen et al., Chapter 17, this volume) |
| Risk factors for diseases | Community resilience capacity Joint health-care provision to remote populations (Schelling et al., 2007; Häsler et al., Chapter 10, this volume) |
Box 3.1. A systems approach to conservation: black-footed ferret case study.
Black-footed ferrets (Mustela nigripes) are one of North America’s most endangered mammals. A major impediment to survival of this species is sylvatic plague (caused by the bacterium Yersinia pestis) as both ferrets and their major food source, prairie dogs, are highly susceptible to this disease. Due to the importance of this disease, sylvatic plague is one of the few wildlife diseases for which a vaccine has been developed and field tested. A combination of the vaccine and insecticides to reduce flea populations that carry the plague bacteria are used to control plague outbreaks on the landscape (Roth, 2019). Although disease management will be essential for survival of black-footed ferrets, it is not the only strategy needed to ensure their recovery. Ferret reintroduction efforts are also impeded by factors such as eradication of prairie dogs in some parts of their native range as they are considered agricultural pests (Casper et al., 2018). Human values such as landowner views of prairie dogs as pests will be critical to address to ensure the long-term recovery of ferrets.
Human, animal and ecosystem health
A shift in focus from a reductionist disease-centric view to a systems-oriented, health-centric model requires a common understanding of what falls under the umbrella of ‘health’. Human health has been variably defined as ‘freedom from disease’ (Boorse, 1977), ‘ability to perform valued social roles’ (Stokes et al., 1982), ‘complete physical, mental, and social well-being’ (WHO, 1948) and ‘capacity to adapt, respond to, or control life’s challenges’ (Frankish et al., 1996). One reason that the definition continues to evolve is that health is not an objective state, but rather a construct dependent on human ideas and values (Hanisch et al., 2012; Lerner and Zinsstag, Chapter 5, this volume). When defining animal health, the value and function of the animal in relationship to humans plays a role. For instance, the criteria used for evaluating the health of a pet dog, valued for companionship, will be different from those used when considering the health of a dairy cow, valued for production. Similarly, for wildlife, ideal survival rates, reproduction rates, or disease prevalence in a population will be determined by human values and are likely to differ for an endangered species compared with a nuisance species as well as among stakeholder groups (e.g. wildlife enthusiasts, animal rights activists, tourism facilities, livestock farmers, land managers and land owners).
Considering health as the capacity of populations to cope with change (Stephen, 2014) emphasizes characteristics that affect vulnerability and resilience (Obrist et al., 2010; Zinsstag et al., Chapter 31, this volume) and could be used to fortify health in the face of uncertainty rather than waiting to address hazards after they emerge (Stephen, 2016). In wildlife as in humans, capacity to cope with change is influenced by interacting biological, social, societal and environmental determinants. As such, health can be assessed indirectly by assessing these determinants, including hazards, such as disease, and promoters, such as biodiversity and habitat quality (Allen et al., 2011). To this end, determinants of wildlife health models based on a human public health model has been proposed (Wittrock et al., 2019). The determinants influencing wildlife health can include factors related to: (i) biological endowment (e.g. genetics, age, reproductive status, disease); (ii) social environment (e.g. population demographics, interspecies and intraspecies competition); (iii) access to needs for daily living (e.g. quality habitat and food); (iv) abiotic environment (e.g. climate and anthropogenic pressures); (v) direct mortality (e.g. hunting and predation); and (vi) human expectations (e.g. policies and stakeholder values). Importantly, these factors were considered likely to be of practical significance to both wildlife managers and the scientists who provide data on which management decisions are based (Wittrock
