“One Health” From Concept to Application in the Global World

Maria Cristina Schneider; Claudia Munoz-Zanzi; Kyung-duk Min; Sylvain Aldighieri

doi:10.1093/acrefore/9780190632366.013.29

Summary

The vision that everything is connected in this world is not new. However, to respond to the current challenges that the world is facing, the integrated vision that humans, animals, and the environment are linked is more important than ever. Collaboration among multiple disciplines is crucial, and this approach is fundamental to understanding the One Health concept.

A transdisciplinary definition of One Health views animals, humans, and their shared settings or environment as linked and affected by the socioeconomic interest of humans and external pressures. A One Health concept calls for various disciplines to work together to provide new methods and tools for research and implementation of effective services to support the formulation of norms, regulations, and policies to the benefit of humanity, animals, and the environment for current and future generations. This will improve the understanding of health and disease processes as well as prediction, detection, prevention, and control of infectious hazards and other issues affecting health and well-being in the human-animal-ecosystem interface, contributing to sustainable development goals, and to improving equity in the world.

Why the “One Health” Approach Is Important

The importance of the connection among humans, animal and the environment in this world is not new. However, to respond the current challenges that the world is facing, the integrated vision that we are all linked has never been so important, and collaboration among multiple disciplines so crucial. As an introduction, this section presents a brief review of the global context and some suggestions as to why the One Health approach could be beneficial to better understanding and better performance in this setting. This section reviews the global context and describes how the One Health approach could be beneficial to better understanding and performance in this setting.¹

Demographics

The estimated world population in 2017 was 7.6 billion and is expected to reach 8.6 billion in 2030 and 9.8 billion in 2050 (United Nations, 2017). This trend is expected to continue, with around 83 million people being added each year, even as fertility levels continue to decline. From 2017 to 2050, it is expected that half of the world’s population growth will be concentrated in just nine countries. In order of their expected contribution to total growth, those countries are India, Nigeria, the Democratic Republic of the Congo, Pakistan, Ethiopia, the United Republic of Tanzania, the United States, Uganda, and Indonesia. The concentration of global population growth in some less affluent countries may present a considerable challenge to their governments in implementing the United Nations’ 2030 Agenda for Sustainable Development (Box 1).

Why Demographics Matter in the One Health Approach

As the world’s population grows, the demand for food increases. According to the Food and Agriculture Organization of the United Nations (FAO), the human food chain continuously experiences threats from an increasing number of outbreaks of transnational animal and plant diseases and pests and food safety (FAO, 2018). These threats to the human food chain may impact human health, food security, livelihoods, national economies, and global markets. Although growth in demand for virtually all food commodities is expected to be less than in the previous decade, food insecurity will remain a critical global concern and the coexistence of malnutrition poses challenges in many countries (OECD & FAO, 2017). Trade will represent a broadly constant share of the sector’s output over the coming decade. Food imports are becoming increasingly important for food security, particularly in parts of Africa and the Middle East. In the last decade, the People’s Republic of China was the main source of growth in demand for commodities (OECD & FAO, 2017). From the One Health perspective, it is important to understand the production chain in this global market and secure the biosafety and biosecurity of the products.

Urbanization

Globally, more people now live in urban areas than in rural areas. In 1950, 30% of the world’s population lived in urban areas. This rose to 54% in 2014 and is projected to be 66% by 2050 (United Nations, 2015c). Urbanization rates vary across the world’s regions, of which the most urbanized are currently Northern America (82%), Latin America and the Caribbean (80%), and Europe (73%) as compared with Asia (48%) and Africa (40%), which combined are home to almost 90% of the world’s rural population of close to 3.4 billion (United Nations, 2015c). Just three countries—India, China, and Nigeria—together are expected to account for 37% of the projected growth in the world’s urban population between 2014 and 2050. Close to half of the world’s urban dwellers live in settlements of fewer than 500,000 inhabitants, while around 10% live in a megacity of at least 10 million inhabitants (United Nations, 2015c).

Why Urbanization Matters in the One Health Approach

Higher population density, especially in poor countries, can increase contact among people and facilitate the transmission of diseases, as was seen during the Ebola outbreak in 2015 (World Health Organization (WHO), 2015). Rapid urbanization implies close proximity with companion animals, and specifically with rodents, as well as greater needs for sanitation and waste disposal in crowded urban settings. On the other hand, rural populations in least-developed countries rely on their animals as a protein source or to help in agriculture, and many live in areas close to forests and in close contact with wild animals.

Poverty and Income Equality

Around 10% of the global population in 2013 was living in extreme poverty (by the international definition of living on less than $1.90 per day; World Bank, 2016). Efforts to end extreme poverty are far from over and a number of challenges remain to achieving this main goal as those in extreme poverty often live in remote areas and fragile contexts. Even though the proportion of people living in extreme poverty globally has gradually decreased from almost 4 in 10 people in 1990 to just over 1 in 10 in 2013, more than 767 million people are affected (World Bank). Although economic indicators suggest that more people are moving out of extreme poverty and that in some regions such as Latin America and the Caribbean the middle class is growing (World Bank, 2012), poverty levels are still unacceptably high.

The World Bank (2016) reported that the income gap had widened in 34 of 83 countries monitored, with incomes growing faster among the wealthiest 60% than the bottom 40%. Nonetheless, within-country inequality had decreased in many places since 2008.

Why Poverty Matters in the One Health Approach

The first of the eight Millennium Development Goals (MDGs) defined by the United Nations (2015a) was to eradicate extreme poverty and hunger by 2015. For the developing regions as a whole, the share of undernourished people in the total population reduced from 23.3% in 1990–1992 to 12.9% in 2014–2016. Some regions have shown fast progress, such as Latin America, parts of Asia and Africa and the Caucasus, and 72 of 129 developing countries monitored by FAO reached the MDG 1c hunger target (FAO, 2018c). Most of these benefited from stable political conditions and economic growth, often accompanied by social protection policies that targeted vulnerable population groups. Many countries that did not reach the MDG hunger targets had experienced natural or human-induced disasters or political instability, resulting in long-term crises with increased vulnerability and food insecurity for much of the population (FAO, 2018b).

Despite the decline in global poverty and undernourishment rates, around 815 million people are still undernourished. Economic growth is key to reducing undernourishment, but it has to be inclusive and provide opportunities for improving the livelihoods of the poor. One key to progress is to enhance the productivity and incomes of smallholder family farmers (FAO, 2018b). The UN General Assembly in 2015 adopted the resolution of “Transforming Our World: The 2030 Agenda for Sustainable Development,” which recognized the eradication of poverty as the greatest global challenge and an indispensable requirement for sustainable development (United Nations, 2015b). The One Health approach is crucial to reducing hunger and extreme poverty, primarily in rural populations in developing countries.

Box 1. United Nations Sustainable Development Goals

Migration and Displacement

Recent events in the Middle East and North Africa triggered a dramatic increase in migration and the number of refugees around the world, creating one of the largest humanitarian emergencies of our era. According to the UN Refugee Agency (2018), levels of displacement are the highest on record, with 65.6 million people forced from their homes. Among them are nearly 22.5 million refugees, over half of whom are under the age of 18. Thirty percent of displaced people are being hosted in Africa, 26% in the Middle East and North Africa, 17% in Europe, 16% in the Americas, and 11% in Asia and Pacific.

Why Migration and Population Displacement Matter in the One Health Approach

Displaced people often are in situations of overcrowding, inadequate sanitation, and poor access to health services, all of which create the potential for the spread of communicable diseases (Schneider et al., 2012). Things that displaced people need include drinking water, safe food, the means to safely prepare meals, pest control for camps, waste disposal and sanitation, and many other requisites for basic dignity in life.

Infectious Hazards and Epidemics

Studies have found that around 70% of infectious hazard threats to public health have an interface with animals (Chomel, Belotto, & Meslin, 2007; Schneider et al., 2011; Taylor, Latham, & Woolhouse, 2001). Taylor et al. (2001) found that an estimated 61% of human pathogens worldwide have been classified as zoonoses, a subgroup that comprises 75% of all emerging pathogens of the past decade previous to their study (Taylor et al., 2001). The emergence of new strains is always a possibility, as has occurred with the Ebola virus, human immunodeficiency virus (HIV), severe acute respiratory syndrome (SARS), influenza A (H5N1) with a pandemic potential, West Nile virus, and the novel influenza A (H1N1) virus (Centers for Disease Control and Prevention (CDC), 2003; Fraser et al., 2009; Jones et al., 2008; Webster, Peiris, Chen, & Guan, 2006). At the same time, very old and well-known infectious hazards such as rabies, plague, and anthrax still persist and continue to produce outbreaks and potential public health emergencies of international concern (PHEIC) and damage to animal health (Cleaveland, 2014; Schneider et al., 2014).

The World Health Organization (WHO) issued its revised International Health Regulations (IHRs) in 2005 to “help the international community prevent and respond to acute public health risks that have the potential to cross borders and threaten people worldwide” (WHO, 2008) (Box 2). A study by the Pan American Health Organization (PAHO) quantified the importance of the diseases common to animals and humans in events recorded by the Event Managements System/IHR for the Region of the Americas, and concluded that approximately 70% of events reported were within the animal–human health interface (Schneider et al., 2011).

Why Infectious Hazards and Epidemics Matter in the One Health Approach

Diseases have the potential to transcend geopolitical boundaries through international travel and trade. The economies and livelihoods of the entire international community can be affected by a single health crisis in one country. Three PHEICs have been declared since the implementation of the new IHR: influenza A (H1N1) in 2009, Ebola virus in 2013, and Zika virus in 2015. These events occurred within the human–animal–environment interface. In some epidemics, such as influenza, animals play a major role in the interface, whereas in others such as Zika virus they are only accidental hosts. For Ebola virus, the ecosystem characteristics have been studied for several decades and are well described (Morvan, Nakouné, Deubel, & Colyn, 2000; Muyembe-Tamfum et al., 2012). Other events reported since the new IHR have also had an interface with animals or with the environment and were not classed as PHEICs, but were nonetheless also sources of much concern internationally, such as Middle East respiratory syndrome (MERS) in the Middle East (WHO, 2013), cholera in Haiti and Yemen (WHO, 2018), and yellow fever in Africa and Brazil (PAHO, 2018).

Box 2. International Health Regulations

The International Health Regulations (IHR) are an international legal instrument that is binding in 196 countries across the globe, including all the member states of WHO (WHO, 2016). The aim of the regulations is to help the international community prevent and respond to acute public health risks that have the potential to cross borders and threaten people worldwide.

For that purpose and as part of IHR implementation, WHO member states are committed to strengthening their surveillance of and ability to rapidly detect, assess, notify, and report potential public health emergencies of international concern (PHEICs) in accordance with these regulations.

PHEICs are extraordinary events— that have been determined, as provided in the IHR, to “constitute a public health risk to other States through the international spread of disease. . . and potentially require a coordinated international response” (WHO, 2016).

Events are identified as potential PHEICs and reported to the six WHO IHR (2008) Regional Contact Points when they fulfill at least two of the following four criteria

a serious public health event is suspected

the event is considered unusual or unexpected

there is a significant risk of international spread

the event poses a significant risk to international travel or trade (2).

Events that have been reported or detected as potential PHEICs are entered into a database known as the Event Management System, which is administered by WHO.

The IHRs, which entered into force on June 15, 2007, require countries to report certain disease outbreaks and public health events to WHO. Building on the unique experience of WHO in global disease surveillance, alert, and response, the IHRs define the rights and obligations of countries to report public health events and establish a number of procedures that the WHO must follow in its work to uphold global public health security.

Source. WHO (2016).

Trade, Tourism, and the Global Economy

Animal-origin food products are considered a commodity, and according to the OEDC–FAO Agricultural Outlook report (2017), global food commodity prices are projected to remain low over the next decade compared to previous peaks, as demand growth in a number of emerging economies is expected to slow down. Additional calories and protein consumption are expected to come mainly from vegetable oil, sugar, and dairy products, whereas growth in demand for meat is projected to reduce, with no new sources of demand to maintain the momentum previously generated by China.

FAO data show that milk was the highest livestock product in tonnes during 2014 (652,351,920 tonnes of cow milk and 107,764,334 of buffalo milk); followed by pig meat (115,313,734); chicken meat (100,352,826); eggs (69,790,757); and cattle meat (64,681,068 tonnes). At close to half of the world’s production, the Americas are the largest producers and exporters of cattle and chicken meat (FAO, 2018).

Around 10% of gross domestic product (GDP) globally comes from tourism and this has been increasing in recent years (World Bank, 2015). The tourism sector creates jobs and is an opportunity for developing countries with natural and cultural assets.

Why Trade, Tourism, and Global Economy Matter in the One Health Approach

For some common animal diseases, the appearance of cases in one country can have an important impact on trade related to animal products in others. This effect was observed across several countries in the case of avian influenza A (H5N1) in 2006 (Burns, van der Mensbrugghe, & Timmer, 2006). Although H5N1 was not detected in the Americas, there was a 40% drop in the share values of large poultry producers due to the indirect impact of the global market (Newcomb, 2008).

Economic losses in trade due to diseases in the animal–human interface have been estimated in billions of dollars. For example, the global economic losses from SARS were estimated to be $40–50 billion, and there was even a significant impact on the GDP of Canada and of Asian countries (Newcomb, 2008). Another study estimated that economic losses were in excess of $125 billion, considering the broader economic cost of some diseases affecting people and animals globally in the period 1995–2008 (Newcomb, 2008). The World Bank also estimated economic losses of at least $80 billion related to six zoonotic disease outbreaks between 1997 and 2009 (World Bank, 2012). In addition, there were high indirect costs from SARS; for example, the psychological impact on hospital workers in Canada and anxiety in affected communities in Hong Kong (Leung et al., 2004; Nickell et al., 2004).

Many of the disease outbreaks in the interface created tension in travel and tourism, even though WHO recommends not to restrict entry of people originating from affected countries. During the SARS outbreak, tourism profits fell by 15–40% in Asian countries (Newcomb, 2008).

Climate Change

Climate change is affecting every country, disrupting national economies, and affecting lives (United Nations, 2015a). People are experiencing its significant impacts, which include rising sea level, changing weather patterns, and more extreme weather events. It is already costing communities and countries dearly and this will only increase, with the poorest and most vulnerable people being most affected (United Nations, 2015a).

According to WHO, climate change affects the social and environmental determinants of health: clean air, safe drinking water, sufficient food, and secure shelter (WHO, 2017). Between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year from malnutrition, malaria, diarrhea, and heat stress.

Within the past decade, record-breaking and devastating rainfall events have occurred, and 2010 was ranked the wettest year on record (Coumou & Rahmstorf, 2012). Disasters may increase in frequency, along with an increase in the intensity of extreme weather events such as heatwaves, droughts, heavy rainfall, storms, and an expansion in areas affected by droughts and floods (Meehl et al., 2007).

Why Climate Change Matters in the One Health Approach

The topic of infectious diseases following natural disasters has been studied for many years in all regions of the world (Ligon, Spiegel, Le, Ververs, & Salama, 2007; Watson, Gayer, & Connolly, 2007). Rain and floods are considered primary risk factors for leptospirosis, cholera, and diarrhea outbreaks, as well as for many other communicable diseases (Schneider et al., 2012).

Climate-related extreme events have severe consequences for human and animal health and food and water safety and security, particularly for poor coastal and island communities and populations dependent on agriculture and natural resources (Schneider et al., 2012). Climate change may increase the susceptibility of animals to disease, increase the range or abundance of vectors/animal reservoirs; prolong vector transmission cycles, increase vulnerability of particular social groups and economic sectors due to extreme weather events and ecosystem stress, and impact on farming husbandry practices, including the use of veterinary drugs (Tirado, Clarke, Jaykus, & McQuatters-Gollop, 2010). Also, according to the FAO (2018a), climate change threatens our ability to achieve global food security, eradicate poverty and achieve sustainable development. Climate change has both direct and indirect effects on agricultural productivity, including changing rainfall patterns, drought, flooding, and the geographical redistribution of pests and diseases.

History of an Integrated One Health Concept

Throughout the history of humankind, there has always been a view that humans and animals are connected. Rabies is a good example to illustrate this connection. In The Iliad, Homer referred to rabies and the malignant influence of Sirius—the dog star of the constellation Canis Major, or Orion’s dog—on the health of mankind, and compared the invincible Hector to a rabid dog (Baer, 1975; Schneider & Santos-Burgoa, 1994). Zinsstag, Schelling, Waltner-Toews, and Tanner (2011) reviewed the history of integrative thinking around human and animal health, which started with ancient healers who cared for both humans and animals. Egyptian papyri from 1800 bc describe human and animal disease and the Zhou dynasty in China (11th–13th century) had one of the earliest organizations of an integrated public health system to include medical doctors and veterinarians.

The 19th-century German physician, naturalist, anthropologist, and politician Rudolf Virchow is considered the “father of modern pathology” (Magalhaes, 2010). With the advance of cellular pathology came an interest in linking human and animal medicine as a form of comparative medicine, based on the discovery of similarities in the disease processes in human and animals (Zinsstag et al., 2011). Virchow was also an important public health professional, and he supported the idea of dividing epidemics into natural and cultural, considering the latter to be a product of disturbances experienced by society. He and his contemporaries supported the concept of a unified science (Magalhaes, 2010). William Osler, a Canadian physician and pathologist, was a student of Virchow’s. Osler, who is widely considered to be the father of modern medicine, brought this integrated medical thinking to North America (Cardiff, Ward, & Barthold, 2008). Osler’s deep interest in the linkages between human and veterinary medicine is described in his work “The Relation of Animals to Man.”

In the Americas of the late 1940s, the important role of animals in the epidemiology of zoonotic diseases was recognized, including how these diseases could spread and how they could be controlled. In 1947, James Steele founded the Veterinary Public Health Division at the Communicable Disease Center (now Centers for Disease Control and Prevention, CDC) in the United States. This division played an important role in the public health response to diseases such as rabies, brucellosis, salmonellosis, Q fever, bovine tuberculosis, and leptospirosis. The application of veterinary science in public health was introduced to other countries in the Americas and around the world. The first “Report of the Zoonosis Commission in the Region” was published in 1947 and the Veterinary Public Health Program at PAHO was created in 1949 (WHO, 2002). Rabies was one of the priority zoonotic diseases for control at that time in the Americas. A joint health and agriculture surveillance system for rabies was created in the late 1960s, and cases in humans and animals (domestic and wild) in all countries of the region were reported in the same surveillance bulletin, periodically distributed by PAHO (OPS, 2018).

In the 1970s, Calvin Schwabe, an American veterinarian, rethought the term “one medicine” and is recognized for having coined the concept that fully recognized the close systemic interaction of humans and animals for nutrition, livelihood, and health (Zinsstag et al., 2011). Schwabe rearticulated concepts from Virchow in the 1964 edition of Veterinary Medicine and Human Health (Schultz, 2011). The concept of “one medicine” was much used by pathologists in the development of new cross-species treatments and vaccines and in other experimental studies in animals that would benefit human health.

New zoonotic diseases have been discovered continually but have not always appeared as a serious public health impact at that moment. For instance, the Zika virus first appeared in the late 1940s (Zanluca et al., 2015) and the Ebola virus in the 1970s (Muyembe-Tamfum et al., 2012), both in small villages in Africa, but it was some decades later when the diseases appeared in large cities that they became public health emergencies of international concern (WHO, 2014, 2017).

In the 1990s the world experienced the emergence of new threats in the animal–human health interface, including bovine spongiform encephalopathy (BSE), or “mad cow disease,” and SARS, which had serious impact on the economy, travel, and society (Kuo, Chen, Tseng, Ju, & Huang, 2008; Newcomb, 2008; Nickell et al., 2004). In 2003 outbreaks of avian influenza A were reported in Asia and the disease posed a potential pandemic threat with significant economic repercussions. Trade disruption and the decline in international tourism were estimated to cause billions of dollars in global economic losses in addition to significant social impact (Kuo et al., 2008; Newcomb, 2008; Rushton, Viscarra, & Bleich, 2005). The constant threat of new pandemics originating in the animal–human interface demonstrates the fundamental need for intersectoral collaboration, especially in surveillance, risk management, biosafety, and communication. It was in this context that the concept of One Health emerged.

In 2004, the Wildlife Conservation Society organized a symposium in New York City on “Building Interdisciplinary Bridges to Health in a Globalized World.” The result was a list of 12 recommendations, the Manhattan Principles, that urged world leaders, civil society, the global health community, and scientific institutions to adopt a holistic approach to the prevention and combat of epidemic/epizootic diseases and the maintenance of ecosystem integrity (CDC, 2004). Soon, the principles became known as the One World, One Health concept.

Many meetings and frameworks based on this approach have been organized (Box 3). During the 2007 International Ministerial Conference on Avian and Pandemic Influenza in New Delhi, it was recommended that a medium-term strategy be developed to address emerging infectious diseases. In response, WHO, the World Organization for Animal Health (OIE), FAO, the United Nations Children’s Fund (UNICEF), the World Bank, and the United Nations System Influenza Coordination (UNSIC) developed a multi-institutional collaboration to prevent, detect, control, manage, and eliminate diseases in the human–animal interface (FAO, OIE, & WHO, 2008, 2010). This collaboration across international organizations focused on supporting member countries to minimize the burden of monitoring and reporting, maximizing support, and avoiding duplication of efforts.

Box 3. One Health Meetings

2015: 2nd Global Health Forum One Health Summit. Davos, Switzerland.

Source: http://onehealth.grforum.org/

2013: Prince Mahidol Award Conference: A World United Against Infectious Diseases; Cross-sectoral Solutions. Bangkok, Thailand.

Source: http://www.onehealthinitiative.com/publications/2013-Conference-Program.pdf

2013: One Health Central and Eastern Africa First International One Health Conference. Addis Ababa, Ethiopia.

Source: https://penaph.net/2013/07/01/first-international-ochea-one-health-conference-addis-ababa-23-27-sept-2013/

2012: One Health Summit, “One Health, One Planet, One Future.” Davos, Switzerland.

Source: http://onehealth.grforum.org

2011: High Level Technical Meeting to Address Health Risks at the Human–Animal–Ecosystems Interfaces. Mexico City, Mexico.

Source: http://apps.who.int/iris/bitstream/10665/78100/1/9789241504676_eng.pdf

2009: One World, One Health: From Ideas to Action. Winnipeg, Canada.

Source: http://www.phac-aspc.gc.ca/owoh-umus/index-eng.php

2008: The 6th International Ministerial Conference on Avian and Pandemic Influenza. Sharm el-Sheikh, Egypt.

Source: http://www.fao.org/docrep/011/aj137e/aj137e00.htm; https://www.oie.int/doc/ged/D5894.PDF

2008: FAO–OIE–WHO with UNICEF, UNSIC, and the World Bank: A Strategic Framework for Reducing Risks of Infectious Diseases at the Animal–Human–Ecosystems Interface.Verona, Italy.

Source: ftp://ftp.fao.org/docrep/fao/011/aj137e/aj137e00.pdf

2007: International Ministerial Conference on Avian and Pandemic Influenza. New Delhi, India.

Source: http://www.fao.org/docs/eims/upload/237162/ah695e.pdf.

Since that time, other global concepts have emerged on the complex interaction between ecosystems and human health, giving rise to the terms “eco-health” or “ecosystem approaches to health.” This recognizes that well-being and health are the results of complex and dynamic interactions between people, ecosystems, and social and economic determinants (Lebel, 2003). Complex system approaches have been used to analyze the occurrence of zoonotic outbreaks (Schneider, 1995), as well as other conceptual frameworks considering the animal–human interface. In addition to supporting an interdisciplinary collaboration between human and veterinary medicine with a substantial focus on zoonoses, One Health has evolved into a broader and more holistic paradigm that includes ecological, economic, and social dimensions (Global Risk Forum, 2015).

The Concept

The One Health concept seeks to integrate human, animal, and environmental health for the prediction and control of diseases in the human–animal–ecosystem interface (Coker et al., 2011; Kaplan, Kahn, & Monath, 2009; Rabinowitz et al., 2013). It is also defined as an effort to collaborate across multiple disciplines on the local, national, and global level to achieve optimal health for people, animals, and the environment (Frank, 2008; Kaplan et al., 2009; King, 2013).

For Kaplan et al. (2009), the One Medicine, One Health concept recognizes a unity of purpose, irrespective of anachronistic barriers and obstructions, in which close collaboration and communication across the various disciplines of human and veterinary medicine and other sciences is a powerful strategy. This approach recognizes the need for leaders in the public, animal, and environmental health fields to conduct research, generate evidence, and guide public-policy decision makers through issues involving multiple sectors. The objective is to reduce the emergence and re-emergence of zoonotic diseases (Coker et al., 2011; Kakkar & Abbas, 2011) and other events of importance at the human–environment–animal interface.

In order to clarify the working definition of the One Health approach, the Stone Mountain Working Group specified the following principles:

It is feasible to integrate efforts in human, animal, and environmental health to predict and control certain diseases at the human–animal–ecosystem interface.

Integrated approaches that take into account human, animal, and environmental health components can improve prediction and control of certain diseases (Rabinowitz et al., 2013).

Boxes 4 (leptospirosis) and 5 (avian influenza) describe examples of applications of the working definition of the One Health (Rabinowitz et al., 2013) approach on events at the animal–human–ecosystem interface including possible suggestions for integrated action to predict, detect, prevent, and respond to the event.

Box 4. Leptospirosis as an Example of Possible Application of the Operational Concept of One Health

Box 5. Avian Influenza (H5N1) as an Example of Possible Application of the Operational Concept of One Health

The definition of One Health as a “collaborative effort of multiple disciplines . . . to attain optimal health for humans and animals while protecting the environment” (King et al., 2008) is fitting, considering the importance of multidisciplinary approaches in research, education, services, and policies, which are fundamental for building solid scientific evidence for decision-making in health. However, the definition of One Health currently used by the CDC has been expanded to include the concept of “transdisciplinarity” (CDC, 2018). Transdisciplinarity has been defined as “efforts conducted by professionals from different disciplines working jointly to create new conceptual, methodological, and translational innovations that integrate and move beyond discipline-specific approaches to address a common problem” (Harvard Transdisciplinary Research in Energetics and Cancer Center, 2018). According to German philosopher Jurgen Mittelstrass (2011) transdisciplinarity “is intended to imply that cooperation will lead to an enduring and systematic scientific order that will change the outlook of subject matters and disciplines . . . it is a principle of research and science, one which becomes operative wherever it is impossible to define or attempt to solve problems within the boundaries of subjects or disciplines, or where one goes beyond such definitions” (Mittelstrass, 2011, p. 331). Choi (2006) discussed the use of the definitions of multidisciplinarity, interdisciplinarity, and transdisciplinarity in health research, services, education, and policy (Box 6).

Box 6. Multidisciplinarity, Interdisciplinarity, and Transdisciplinarity Defined

Multidisciplinarity draws on knowledge from different disciplines but stays within its boundaries.

Interdisciplinarity analyzes, synthesizes and harmonizes links between disciplines into a coordinated and coherent whole.

Transdisciplinarity integrates the natural, social and health sciences in a humanities context, and transcends their traditional boundaries.

Source. Choi (2006).

For the authors of this article, the concept of One Health is based on the integrated vision of how humans interact with animals and with the environment and how professionals in different disciplines can work side by side toward a common goal. Early work by Schneider (1984) at the local level in a community health project where physicians, nurses, veterinarians, social workers, and others were part of a health team working in close collaboration with the community in a low-income area in Brazil, provided an opportunity to learn about multidisciplinary collaboration focus in a specific community context. This was followed by other experiences in the context of rabies, from local to international level, which also were implemented using this integrated vision. This led to studies of complex systems theory (Garcia, 1986) and reflections on theoretical integrated frameworks that could be used to better understand the occurrence of infectious disease outbreaks in the Americas (Schneider, 1995).

A transdisciplinary definition of One Health views how animals, humans, and their shared settings or environment (such as ecosystem, soil, climate) are linked and are affected by the socioeconomic interest of humans (such as food production, trade, tourism) and external pressures (such as urbanization, migration, demographics). It also considers how different disciplines can together provide new methods and tools for research and implementation of effective services to support the formulation of norms, regulations, and policies to the benefit of humanity and animals, while considering the environment, for current and future generations. This approach will improve prediction, detection, prevention, and control of infectious hazards and other issues affecting health and well-being in the interface and contribute to the UN’s Sustainable Development Goals to help to improve equity in the world.

Figure 1 shows the application of the theory of complex systems to a specific real case. A critical area (“hot spot”) with a high number of human cases of leptospirosis was identified in the Central Region of Rio Grande do Sul state, Brazil (RS), and environmental and socioeconomic drivers where analyzed (Schneider et al., 2015). This critical area (RS Central Region) was considered as a system. Subsystems were defined to better understand the setting or context of RS: the physical/ecosystem/environmental subsystem (P); agro-productive subsystem (A); socioeconomic subsystem (S); and health subsystem (H). There are interconnections between the subsystems, such as (1) from P to A, possible interrelations could be the type of ecoregion, soil type, amount of rainfall, proximity to rivers and other natural elements that are suitable for certain types of crops (such as tobacco, rice, or corn), and the system of cattle raising (intensive or free-range); (2) from A to P, possible interrelations could be deforestation or excessive use of the soil for crop production; (3) from S to A, interrelations might include the tendency in the region for smaller-sized properties, provision of economic incentives for certain types of crops (productive process) such as tobacco, historical incentives for European immigration to the area, and easier access to land; (4) from A to S, an example of an interrelation might be that tobacco is a profitable commodity, which provides better living conditions for the people who plant and sell it than other commodities; (5) from S to H, it could be that if the majority of inhabitants of this area have higher economic standards than in other agro-productive areas they also have better conditions for lower illiteracy, higher-quality medical care, and less health inequality; (6) from H to S, if the people of this area were wealthier then they could work and live longer in general; (7) from P to H, if this ecoregion had a good climate suitable for crops and raising animals, it would facilitate good nutrition and general health. In summary, the suggested external conditions of this system in RS Central Region could be (a) the inflow of people from the immigration policies decades ago; (b) land distribution; (c) high quality agriculture work; (d) economic incentives for tobacco production; and (e) agrobusiness policies. Outgoing flow from the system could be (f) tobacco products; (g) other agricultural products; (h) trade; (i) government taxes; and (j) monetary exchange.

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Figure 1. A systemic approach to leptospirosis in a “hot spot” in Rio Grande do Sul state, Brazil, using the definition for One Health suggested by the authors.

Subsystems: P, Physical/ecosystem/environment; A, Agro productive; S, Socioeconomic; H, Health system

Interrelations among the subsystems:

Between P and A: type of ecoregion, soil, rainfall, proximity to rivers

From A to P: deforestation, excessive use of the soils for plantations

Between S and A: small properties, economic incentives provided to certain types of plantations (i.e., tobacco)

From A to S: tobacco is a profitable commodity; better life conditions

From S to H: higher economic standards, high quality medical care, lower illiteracy and less health inequality

From H to S: wealthier people, longer life

From P to H: good climate suitable for crops and raising animals, good nutrition

In Figure 2, six maps illustrate the subsystems and interrelations in RS Central Region, where the higher number of human leptospirosis cases occurred. Environmental drivers in RS Central Region found associated with leptospirosis in humans were ecoregion (Parana-Paraiba interior forest), soil type, and proximity to rivers. Socioeconomic factors included low rates of illiteracy and higher GDP, which were likely suggestive of increased healthcare access and therefore capacity for case detection, higher GDP, and lower income inequality (Gini index) associated with the extensive agricultural production in the area.

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Figure 2. Environmental and socioeconomic possible drivers related to the critical areas for human leptospirosis cases in Rio Grande do Sul Central Region, Brazil. (a) Ecoregion; (b) Soil type; (c) Proximity to rivers; (d) Rates of illiteracy; (e) GDP; (f) Gini index. a and b were published in Schneider et al. (2015).

Global Applications Using the One Health Concept

To analyze the use of the One Health concept globally, a review of publications about One Health in peer-reviewed journals was performed (methodology in Box 7), followed by a similar internet search focusing on training being offered on this topic. In total, 955 articles were found. After excluding duplicates (168), articles considered irrelevant to One Health because they did not describe a multidisciplinary approach (515), and articles that were not found (61), 201 articles were reviewed (see Box 7 and Fig. 3 for methodology).

Box 7. Research Methodology: One Health in Peer-Reviewed Journals

A scoping review (Peterson, Pearce, Ferguson, & Langford (2017) was done to assess what is being published about One Health. This methodology was chosen in place of a systematic review because a broad search was needed on the various perspectives on One Health and to avoid limiting the search to certain types of study design or topic.

The search was performed between January and March 2017. The search strategy was as follows:

Database: PubMed, Embase

Hand searching: Google, each journal

Terms: Determined after reviewing the review paper (their search strategies)

Search terms for review paper:

PubMed: “One Health” [All Fields] AND review [pt]

Embase: “One Health” AND review

All results were organized into thematic blocks: history, concept, and application (training, research, intervention, and advocacy).

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Figure 3. Flow chart of search results.

Table 1. Articles Found in the Scoping Review on One Health, by Category and Year of Publication

Category	Year											Total
Category	2007	2008	2009	2010	2011	2012	2013	2014	2015	2016	2017 *	Total
History/Concept		1		4	10	5	13	16	9	7	4	69
Application	1	3	4	3	4	7	26	24	24	32	4	132
Total	1	4	4	7	14	12	39	40	33	39	8	201

Source: *Number of publications until March 2017.

The number of articles about One Health increased threefold from 2012 to 2013, when most were on the application of the concept. In almost half of the publications, the first author was located in the Americas (47.3%) followed by Europe (33.3%). The countries that published most on One Health were the United States (76 publications), the United Kingdom (20), and Australia (10). Although there were articles from all continents, the regions with the majority of One Health publications were North America and Europe (Figure 4).

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Figure 4. Distribution of affiliations of the first authors identified in the scoping review of One Health publications.

Health Professionals and One Health

As the importance and the use of One Health approaches grows, the demand for well-trained professionals in relevant disciplines is in high demand. Globally, various academic institutions have established curricula offering graduate degrees in One Health. Veterinary medicine has been the leading discipline in introducing One Health–related training in its curriculum, probably because the veterinary public health concept was already established before the advent of the One Health concept. By expanding the concept development of training programs was simpler for veterinary science than for other disciplines. Selected examples in master’s programs in One Health include the Ross University School of Veterinary Medicine in the United States (Stroud et al., 2016), the Royal Veterinary College/London School of Hygiene and Tropical Medicine in the United Kingdom (Sikkema et al., 2016), and the Universitat Autonoma in Barcelona, Spain. In the United States, many universities have established joint programs combining a doctorate in veterinary medicine (DVM) with a master’s in public health (MPH), which are also mainstream One Health training programs (Stroud et al., 2016). One Health training opportunities in Asia and Africa have increased (McKenzie et al., 2016; Rwego et al., 2016), and many of the programs are established in partnership with foreign institutions, such as Massey University in New Zealand.

The Southeast Asia One Health University Network( comprises universities in Malaysia, Indonesia, Thailand, and Vietnam, and has supported One Health capacity building in various ways, such as providing scholarships for master’s programs or conference grants to attend One Health workshops.

Some academic institutions also offer nondegree short training programs, some of which include fieldwork. These programs can be found on any continent. Current training programs for One Health provide various educational opportunities for professionals from different disciplines. However, the training programs tend to be weighted toward veterinary schools.

Expectations for One Health Professionals

Core competencies for One Health professionals have been the subject of several conferences. Three working groups on essential competencies for One Health professionals were held in Bellagio, Italy (Rockefeller Foundation, 2011); Stone Mountain, United States (Stone Mountain Meeting Workgroups, 2011); and USAID/RESPOND (Global OHCC Working Group, 2013). The Rockefeller Foundation, CDC, and FAO, together with the University of Minnesota, sponsored a meeting in Rome to synthesize One Health Global Core Competencies. The core competency domains categorized were similar, despite the different approaches of each meeting (Frankson et al., 2016) (Figure 5). The resulting framework is not very different from the core competencies for Global Health as proposed by the Consortium of Universities for Global Health (Jogerst et al., 2015). Comparing both sets of core competencies, it could be suggested that the One Health core competencies tend to focus more on collaboration among diverse disciplines, while those for Global Health focus more on domains to provide skills. Both include systems thinking as a competency, referred to as strategic analysis in the Global Health core competencies: “Strategic analysis is the ability to use systems thinking to analyze a diverse range of complex and interrelated factors shaping health trends to formulate programs at the local, national, and international levels” (Jogerst et al., 2015). Global Health also placed more emphasis on skills to better understand the context, which include demographic and sociocultural aspects besides environmental ones (Figure 5).

The competencies cited in these publications from One Health groups (Frankson et al., 2016) are all relevant. However, one more domain could be proposed that is very close to the “systems thinking” mentioned in the publications and closer to the domain cited for Global Health professionals. We suggest the term “drivers analysis.” To define what types of collaboration are needed and also to create policies and regulations, it is necessary to understand the possible factors on a larger scale (not only individual risk factors), for example those related to the occurrence of a disease or an event.

This will imply a shift in paradigm, whereby the various disciplines transcend their traditional boundaries and create a new way to approach a common problem related to the animal–human–ecosystem interface. Studies on leptospirosis (Bacallao, 2014; Schneider, 2012, 2015) have suggested drivers related to ecoregions, soil type, productive process (land use), and concentration of animals by property (Schneider, 2012, 2015). Cases of leptospirosis were also related to socioeconomic factors, such as poverty, lack of sanitation, and poor housing conditions (Bacallao, 2014). Hamrick’s (2017) study on yellow fever cases in humans found association with geographic and environmental factors.

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Figure 5. Comparison of One Health and Global Health core competency domains. One Health core competency domains re reframed based on descriptions in Frankson et al. (2016), and Global Health core competency domains re based on Jogerst et al. (2015).

Some natural drivers of transmission may not be modifiable (e.g., soil type) and others may be highly fluctuating (e.g. flooded areas); however, this understanding is critical in order to perform risk mapping to support health policies and to establish prevention and control actions. In the case of yellow fever, for example, a control program would consist of active surveillance in nonhuman primates, enhanced detection of human cases, human vaccination in risk areas and in occupational groups, and awareness campaigns in higher risk periods of the year, among others. Transdisciplinary teamwork is necessary to accomplish this. For example, a team that included a medical doctor, veterinarian, epidemiologist, and geographer would analyze the problem with a One Health approach and transform the data-driven recommendations into actions that may involve a public health professional to implement a vaccination campaign, a biologist to collect samples from nonhuman primates, and a communicator to prepare educational materials. Any individual working within the One Health approach does not need all of these skills, as they will likely be working within a team. Nonetheless, they will need to be able to analyze the problem with a holistic and integrated vision including an understanding of social and ecological contexts. Furthermore, it is important to see the team components as fully integrated, with common understanding, language, and goals—more than simply working in cross-discipline teams or sharing information among sectors.

Application of the One Health Concept in Research

A better understanding of the complexity of infectious diseases—in particular zoonotic infections or those with transmission drivers highly influenced by social, environmental, and ecological factors—has resulted in an increased recognition of the role of the One Health concept in research. Although not always stated as such, there has been a renewed interest in multilevel and interdisciplinary research methods (Pearce, 2013). Furthermore, the search for review articles on One Health in research (Box 7) found 15 articles that highlight a role for One Health in research. These articles discussed methods and applications and identified gaps and challenges for collaborative research across disciplines and sectors. Schurer et al. (2016) carried out a systematic review of literature on studies of parasites under a One Health approach. Criteria for One Health research should include humans, animals, and the environment. Only 30 unique publications involved work in all three areas, and most studies were cross-sectional in nature. Overall, fewer studies attempted to include an environmental component and there was a lack of application of appropriate methods in each component and the necessary statistical analysis to link all three components simultaneously. Likely barriers were listed that also apply to other research areas. These included communication in technical language and discipline-specific interactions, data sharing, synching research priorities, budget, and ensuring that team members from the various disciplines remained engaged during the entire study period.

Collaborative research can lead to progress in obtaining a mechanistic understanding of the processes behind pathogen spillover from animals to people. In the context of expansion in the demand for bush meat due to land use changes in some countries, wildlife researchers and ecologists are investigating hunting dynamics and characteristics of the wildlife hunted, as well as the impact on conservation and biodiversity. A One Health concept is applied in order to gain a full understanding of the entire process, from the ecology of the pathogen in the natural reservoir, through pathogen spillover, and public health impact. There is an increasing but still limited number of studies involving wildlife biologists and social and medical researchers investigating pathogens at the wildlife and human interface (Daszak, 2007). A concerted interdisciplinary research effort is needed to increase the prospects to predict spillovers of human disease potential (Morse, 2012). Collaborative research is also critical to evaluate the impact of animal interventions on improving public health and, depending on the disease, animal health as well. In a clear example, a randomized controlled trial showed that combined human and bovine chemotherapy for zoonotic schistosomiasis had a greater effect on human incidence than human treatment alone (Gray, 2009).

Life course epidemiology and the increasing recognition of the importance of the context in which populations live and work (Pearce, 1999) needs a One Health approach—in particular for diseases with complex transmission and in areas with difficulties regarding access and community engagement (Schurer et al., 2016). One example of this is in livestock-associated zoonoses, where there is limited understanding of exposure because it is difficult to quantify exposures, particularly in rural areas where people are exposed in occupational and domestic settings, and contacts and changes in contact are hard to pinpoint (Klous, 2016). A One Health approach to research on farms could engage farmers and their families and apply novel ways to measure exposure and outcomes in people and their animals simultaneously, while also assessing their cultural context, perceptions, and behaviors. In general, there is a need for greater incorporation of environmental and ecological context in understanding human disease processes and to evaluate interventions (Rabinowitz, 2013).

Mathematical models are an important tool for gaining insight on infection dynamics, assessing the impact of infections and diseases, and identifying and predicting the effect of interventions. The complexity of the life cycles and transmission processes of many pathogens of One Health relevance needs an integrated and multidisciplinary approach to develop, parameterize, and apply mathematical models for research and policy. This makes research projects that include mathematical modeling an optimal application of a One Health approach. However, modeling disease emergence at the animal–human interface is less common. For avian influenza, for example, despite the large amount of modeling work on human influenza transmission interventions and some in the transmission of zoonotic influenza within bird populations, there is limited work on modeling it within the interface (Dorjee, 2013). Formal involvement of social sciences throughout the modeling process has been less prominent but should be encouraged in order to help integrate and interpret data. In addition, social science, including qualitative methods, can improve models by providing a social context for the problem and more accurate recommendations for policymaking (Grant, 2016).

Although One Health is often thought of as involving mostly zoonotic infectious diseases, the concept is also applied to research on noncommunicable diseases. Pearce (2013) reviewed examples in which expertise from various disciplines and sectors can join efforts, for example, to understand how exposure during childhood to an environment containing microbes may protect against allergies and allergic asthma and investigate mechanisms and etiology of occupational cancer in meat workers, which some hypothesize could be related to bovine oncogenic retroviruses. Linking animal and human medicine research outside the laboratory setting, as in One Health studies in farms, can help to link benchwork and fieldwork and to foster innovation. Linking human and animal health has also been the effort behind groups investigating the health benefits of human and animal bonds (Bartges, 2017), such as an exercise program for obese persons and their dogs that resulted in weight loss and increased physical activity for both (Kushner, 2006).

The occurrence of outbreaks and the spread of pathogens with animal origin (e.g., SARS, avian influenza) led to the development and funding of collaborative networks and programs with a One Health approach (McKenzie, 2016). With the goal to assist with systemization and quality monitoring, a checklist for One Health Epidemiological Reporting of Evidence (COHERE) has been developed to guide the design and publication format of future One Health studies that truly integrate humans, animals, and environment (Davis, 2017). However, research funding for studies with a One Health approach has received less support and investigators face challenges to fit often complex and large studies into conventional research funding mechanisms. One Health research projects often need larger and longer studies in order to measure incidence and drivers of infection at the human–animal interface and even more so at the human–environment–animal interface. In addition, many zoonotic infections are endemic, have a high burden, and impact public health locally, but they do not have pandemic potential and therefore are less likely to be funding priorities. There is a great need for robust and truly interdisciplinary One Health research on these zoonotic diseases to develop effective, integrated, One Health disease-control policies (McKenzie, 2016).

Application of the One Health Concept in Advocacy and Interventions

With the increase in human cases of avian influenza H5N1 in 2006 in Asia and the risk of transmission to other parts of the world, eminent risk for pandemics and the importance of collaboration among sectors was obvious. Integrated vision was required in the planning of interventions: migratory wild birds could be in contact with and transmit influenza virus to backyard birds and other domestic animals and eventually to humans. Furthermore, a better understanding of the way people, produce, and trade interact are important for global security; for instance, the obvious potential risk of markets with high density of animals and low biosafety and the extensive production of birds and bird products with low biosecurity.

Official documents were communicated on the importance of intersectoral actions (PAHO, 2005; WHO, 2005). Preparedness plans for the Americas were developed with the participation of various sectors. Box 8 summarizes a joint publication by PAHO and the Inter-American Development Bank (IADB) on the importance of collaboration among sectors in the preparedness phase for the potential influenza H5N1 pandemic that never occurred. Many simulation exercises were done with intersectoral and multidisciplinary teams, with actors from different levels.

An influenza pandemic did occur in 2009, but with another virus strain—influenza A (H1N1). Nonetheless, the joint preparedness plan was a good exercise in integrated vision and collaboration, which supported future work in responding to threats. As the first declaration of a Public Health Emergency of International Concern (PHEIC) since the new version of IHR was in place, during the H1N1 pandemic it was even more obvious that stronger collaboration was needed, with advocacy for the One Health approach to better prevent, detect, and respond to pandemic influenza and improve human, animal, and environmental health and well-being (Offeddu, 2016; Pappaionou, 2010; Simms, 2014). The importance of strengthening surveillance across sectors, sharing information, and new tools were among the key points mentioned in many publications (Capua, 2013; Levings, 2012; Schneider, 2007). The development of preparedness plans for response to pandemic influenza through collaboration across sectors was a good exercise in joint vision and effort—and for preparedness to fight any zoonotic disease emergency. However, in some regions, such as Africa, despite these years of influenza preparedness, many countries have built capacity to respond to influenza, but not yet to other zoonotic diseases (Bazeyo, 2013).

Box 8. Integration Between Health and Agriculture in the Preparedness Plans in Latin America

The objective of this study was to highlight the importance of and evaluate the integration between the health and agriculture sectors in preparedness plans in Latin American countries and to provide recommendations on how to fill the potential gaps.

The link between animal and human health with the emergence of pathogenic infectious diseases in the past 20 years, and recent outbreaks of zoonotic diseases, have increasingly drawn public attention to the fact that diseases move back and forth among species.

In 2006, avian influenza was considered an important global threat, when the avian H5N1 strain of the influenza virus was confirmed to have caused more them 250 cases and 150 deaths in humans. While the H5N1 virus had not yet been detected in the Americas, the health risks it represented were unknown, and the economic burden it might carry with it, made it important to prevent this pandemic.

The actors in the preparedness to a possible avian influenza pandemic, with emphasis on health and agriculture, were propelled to the forefront of the global health agenda, and many actors from the sectors of human and animal health and agriculture at different levels were working to prevent its spread and its appearance in humans, and a potential economic impact around the world.

The importance of intersectoral action in preventing and controlling zoonoses, avian influenza in particular, was defined within areas key to the interface between human and animal health, namely: in surveillance that is integrated across sectors; in adequate biosecurity (in this case, ensuring that animals and human food supplies linked to them are protected); in adequate biosafety (in this case, ensuring the protection of people in contact with the virus); and in adequate public information.

Source. Schneider (2017).

The important link between humans and animals in rabies has long been known. The application of combined surveillance, prevention, and control actions to minimize the spread of rabies has been widely recommended (PAHO, 2005; Schneider, 1996; WHO, 2013). One of most common examples is the importance of rabies vaccination coverage in dogs to prevent human cases (Schneider, 2007; Vigilato, 2013). The use of the One Health concept in preventing human cases of rabies from dogs is well documented globally (Cleveland, 2014; Fooks et al., 2014; Meslin, 2013; Rupprecht, 2015).

In addition, the role of the environment and wildlife such as foxes, raccoons, and other animals in rabies transmission to humans is well known, and strategic interventions, including wild-animal vaccination using baits, have been in use for many years (Rupprecht, 2008; Ver Cauteren et al., 2012). Studying human rabies transmitted by hematophagous bats, Schneider (2009) suggested that there were two interrelated groups of factors—biological and nonbiological—as conditions to the occurrence of cases:

Biological factors include the presence of vampire bats, the existence of adequate shelter, the availability of food sources, and the presence of rabies virus in the area. Nonbiological factors include the type of human productive process and changing patterns in such activities, working and living conditions, access to rabies prophylaxis, and measures being implemented to control bat populations.

(Schneider, 2009)

The biological factors are the necessary conditions for maintaining the chain of transmission in the wildlife cycle of bat-transmitted rabies, whereas the structural changes triggered by nonbiological or social factors make the disease emerge, such as in deforestation and gold prospecting. The same rabies example was reviewed using the One Health operational concept (Rabinowitz, 2013) and in a publication about the One Health concept (Schneider, 2014).

Box 9. Rabies as an Example of Possible Application of the Operational Concept of One Health

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Figure 6: Example of One Health vision: One Health in Latin America, rabies transmitted by vampire bat (Desmodus rotundus).

From Schneider (2014).

Vector-borne diseases transmitted by mosquitos, such as arbovirus, are currently in prominence, especially in the Americas. In 2016, the WHO declared Zika virus and its complications as a PHEIC (WHO, 2017), while chikungunya was first recorded in the Americas at the end of 2013 (PAHO, 2013). Many dengue epidemics regularly occur around the world, and other arbovirus diseases are presenting new challenges (WHO, 2017). During 2016 and 2017, yellow fever—another well-known arbovirus—re-emerged in some countries in Africa and in the Americas (PAHO, 2016; WHO, 2017). A study using the One Health approach analyzed human yellow fever cases and the geographic patterns and environmental factors were found to be associated with altitude, rainfall, temperature, and diversity of nonhuman primate hosts (Hamrick, 2017). Several studies advocate the use of the One Health approach in interventions for tickborne pathogens (Dantas-Torres, 2012; De Meneghi, 2016; Mencke, 2013; Vayssier-Taussat, 2015).

Application of the One Health Concept in Antimicrobial Resistance

Antimicrobial resistance (AMR) continues to grow in importance and can only be addressed with the One Health approach. According to King (2016),

over the past few decades, AMR has become a serious and growing global crisis. While the emergence of AMR is not surprising, the speed, scope, and impact of the problem certainly is. The evolution of AMR is now occurring at an alarming rate and is outpacing the development of new countermeasures capable of thwarting bacterial infections in people and animals. This situation threatens patient care, economic growth, public health, agriculture, and national security.

(King, 2016)

AMR occurs when microorganisms adapt after exposure to antimicrobial drugs and become ineffective so microorganisms are able to proliferate (WHO, 2018). For the last 70 years, antibiotics and antimicrobial agents have been an essential aspect of treating patients with infectious diseases. The drugs have been crucial in reducing illness and death (CDC, 2018). Nonetheless, the wide use of these drugs has come at a cost—the infectious organisms the antibiotics are designed to kill have adapted to them, making the drugs less effective (CDC, 2018).

In the United States, at least 2 million people become infected with bacteria that are resistant to antibiotics each year (CDC, 2018). In addition, at least 23,000 people die each year as a direct result of these infections (CDC, 2018). Patients with antimicrobial-resistant bacteria are often hospitalized longer, require additional laboratory tests, and require the use of more expensive drugs, which all adds up to a higher cost of health care (WHO, 2018). Multidrug resistance is also a growing concern for human health. Bacteria are developing resistance to not just one antimicrobial agent, but to several. Globally, approximately 480,000 individuals develop multidrug-resistant human tuberculosis each year, and drug resistance is also complicating the fight against HIV and malaria (WHO, 2018).

In addition to human health, animal health must be considered in any discussion on AMR. Across the globe, in both developing and developed countries, antibiotics are widely used in livestock and agriculture production (Ventola, 2015). The FAO estimates that 27 different antimicrobial classes are used in animals (FAO, 2017). An estimated 80% of antibiotics sold in the United States are used in animals, primarily to prevent infection, improve animal health, and promote growth, resulting in larger yields and a higher-quality end product (Bartlett, Gilbert, & Spellberg, 2013; Ventola, 2015). Unfortunately, the use of antimicrobials in livestock directly translates to the transmission of antimicrobials in the meat and animal products that humans consume. The transfer of antimicrobials to humans ultimately reduces the effectiveness of drugs for treating infection (Food and Drug Administration [FDA], 2018).

The transfer of antimicrobial-resistant bacteria to humans from farm animals was first noted more than 35 years ago, when high rates of antibiotic resistance were found in the intestinal flora and gut of farm animals and farmers. More recently, studies have used molecular detection methods to determine that resistant bacteria in farm animals reach consumers through meat products (Bartlett, Gilbert, & Spellberg, 2013; Ventola, 2015).

There is a growing concern that the routine use of antibiotics in food sources provides strong evolutionary pressure for potentially zoonotic bacteria to develop resistance to antibiotics commonly used to treat humans (Young et al., 2009). Pathogenic bacteria (e.g., Salmonella spp., Campylobacter spp.) and commensal bacteria (e.g., E. coli, Enterococcus spp.), including those carrying resistance genes, can be transmitted from animals to humans through food, by direct contact with animals, or through environmental sources such as contaminated water.

According to the WHO, AMR occurs when microorganisms adapt after exposure to antimicrobial drugs (WHO, 2018). Antimicrobial drugs in this case are ineffective and microorganisms are able to proliferate (WHO, 2018). AMR jeopardizes the effective prevention and treatment of infections caused by bacteria, parasites, viruses, and fungi. AMR is a growing threat to global public health and it is rising at an alarming rate throughout the world. New countermeasure drugs therapies are not being developed fast enough to suppress the bacterial infections in people and animals (King, 2016). This is a dangerous situation threatening several sectors of health including patient care, economic growth, public health, agriculture, and national security (King, 2016). AMR is a public health issue that can effectively be addressed only through collaboration and intersectoral partnership including but not limited to the human health, public health, and veterinary health sectors (Carnevale, 2016).

Given that One Health is at the intersection of human health and animal health, it must be taken into consideration in the response to AMR in both humans and animals. One Health advocates for a holistic and integrated approach involving all three domains (humans, animals, and environment) in order to establish effective AMR approaches (King, 2016). Thinking and acting in three domains rather than one may seem daunting, but a One Health approach to AMR will provide all stakeholders a more comprehensive perspective for intervention generation.

It was estimated that the economic impact of AMR would be $100 trillion (O’Neill, 2014). Previously, AMR had been considered a problem only in human public health, especially in relation to nosocomial infections, and had been relatively ignored in the veterinary and environmental sectors (Robinson et al., 2016). However, as the abuse of antimicrobials in domestic animal husbandry and its potential effects on the human population have become more widely understood (Robinson et al., 2016), the importance of the One Health approach has been highlighted.

AMR is recognized as a growing global threat, and so globally there are several initiatives and organizations devoted to raising awareness of AMR (Box 10). In addition, these groups are advocating for the safe use of antimicrobials in humans, animals, and the environment, in order to mitigate the effects of AMR.

Box 10. Global AMR Initiatives

•

Latin American Network for Antimicrobial Resistance Surveillance (RELAVRA)–PAHO.²

•

Global Action Plan on AMR–WHO/FAO/OIE³

•

The National Antimicrobial Resistance Monitoring System–FDA/USDA/CDC⁴

•

Canadian Integrated Programme for Antimicrobial Resistance Surveillance⁵

•

R&D Collaboration Hub established at the G20 Summit in 2017⁶

•

Asian Network for Surveillance of Resistant Pathogens (ANSORP)

•

European Antimicrobial Resistance Surveillance Network (EARS-Net)⁷

Source. Schneider (2014).

In 2014, the White House announced the National Strategy for Combating Antibiotic-Resistant Bacteria (CARB), underscoring the need to address AMR (FDA, 2018). The FDA Center for Veterinary Medicine has developed a multipronged strategy designed to limit or reverse resistance arising from the use of antibiotics in food-producing animals while continuing to ensure the availability of safe and effective antibiotics for use in animals and humans (FDA, 2018).

The Global Antimicrobial Resistance Surveillance System supports a standardized approach to the collection, analysis, and sharing of data related to AMR at a global level to inform decision-making and drive local, national, and regional action (WHO, 2018). The Global Antibiotic Research and Development Partnership (GARDP) is a joint initiative of WHO and the Drugs for Neglected Diseases initiative (DNDi). GARDP encourages research and development through public–private partnerships. The goal of this partnership is to develop and deliver up to four new treatments through improvement of existing antibiotics and acceleration of the entry of new antibiotic drugs by 2023 (WHO, 2018).

The Global Health Security Agenda suggested AMR as one of the main action packages, emphasizing the importance of One Health approaches in developing national action plans. The UN high-level meeting on AMR held in 2016 clarified the importance of collaborative efforts in its declaration. The One Health approach in AMR has been actualized as a joint surveillance system (European Commission, 2017). The collaborative monitoring approach could provide details of the AMR epidemiological situation and subsequently support related research and legislation on prevention of abuse of antimicrobials.

In 2017, the G20 summit highlighted the importance of international collaboration to address the growing AMR threat through implementation of national action plans using the One Health approach in each country. In addition, the Director-General of the WHO highlighted AMR as “the perfect example of the complex, multisectoral, multistakeholder challenges of the future, requiring more agile, strategic, innovative, and collaborative leadership.” As this is a One World issue, due to the globalization of the food systems, increasing movement of livestock, agricultural produce, and human travel (Robinson et al., 2016), AMR needs to be addressed as a global health priority.

Conclusion

Since One Health was first conceived in 2004, a vast number of initiatives, publications, and training programs have been developed on all continents. Some have arisen around specific diseases or threats and others as a general call for the need to face complex problems from a more holistic perspective and collaborative effort among disciplines and sectors. The concept, scope, and implementation of One Health are still evolving. Nevertheless, all the concepts and examples presented in this article address the key message about One Health: At its core, One Health is based on the notion that humans, animals, and the environment are linked and are part of a large, complex, and interrelated system.

One of the major areas in the application of the One Health approach is in zoonotic infectious diseases such as avian influenza,. Shared data from human and animal surveillance programs are essential to identify the occurrence of strains and to predict their pandemic potential. Research groups working on many other zoonoses and vector-borne diseases with animals in their transmission cycle are also adopting a One Health approach and many other diseases could benefit from it.

More recently, the use of the One Health approach applied to the AMR threat has acquired high visibility. This is an urgent animal health and public health issue that can be addressed effectively only through collaboration and intersectoral partnership—including, but not limited to, the human health, public health, and veterinary health sectors (Carnevale, 2016).

Complex health problems that are rooted in multiple domains cannot be thoroughly investigated using compartmentalized research. One Health research needs to fully integrate other areas and actors not commonly involved in projects, such as ecologists, social scientists, mathematical modelers, and economists (Schurer et al., 2016). The involvement of other disciplines is needed for successful implementation and scaling up of public health interventions). however, in some instances, it may be too late to take advantage of the knowledge brought by the experts in other disciplines. One Health teams working together from the early phase of a research program can benefit from gaining a comprehensive view of the problems, generate new hypotheses, and innovate approaches based on transdisciplinary methods.

Box 11. United Nations Sustainable Development Goals and How They Can Be Supported by the One Health Approach

1. No Poverty

Increase agricultural work opportunities and microfinances in rural areas (with increased animal health and product quality). Decreased impact of diseases that affect ability to work.

2. Zero Hunger

Strengthen mechanisms to improve animal health and sustainable agriculture in communities dependent on production for their livelihood.

3. Good Health and well-being

Collaboration among health, agriculture and other sectors to improve surveillance and response to threats at the interface. Research and training to increase food safety and combat AMR.

4. Quality Education

Support training at all levels about One Health and Sustainable Development Goals

5. Gender Equality

Create inclusive projects with specific roles of women in small business in rural areas. Community health and development programs specifically targeting women. Promote women in leadership roles at all levels.

6. Clean Water and Sanitation

Projects targeting environmentally transmitted pathogens. Water security and quality for people and their animals. Clean disposal of agriculture and animal production waste and residues (antimicrobial residues, pesticides)

7. Affordable and Clean Energy

Support innovations to use modern, clean energy from “farm to table” and finance studies to lower the carbon emission in cattle raising

8. Decent Work and Economic Growth

Create incentives to business owners in all steps from “farm to table” in food production, industrialization, sale, to safe consumption, that increase employment

9. Industry, Innovation and Infrastructure

Finances studies of new technologies and promote projects that considered animal welfare, biosafety, and biosecurity practices in animal food production and their industrialization

10. Reduced Inequalities

Support studies about inequality within and among countries and topics related to the human–animal–ecosystem interface

11. Sustainable cities and communities

Create projects to train and strengthen local health and agriculture and other professionals to better understand and respond to possible threats including natural disasters, epidemics, and AMR

12. Responsible Consumption and production

Support regulations research and programs aimed at industry models that follow AMR guidelines

13. Climate Action

Research to understand the link between climate change and disease. Support reduction of carbon through innovation in production

14. Life Below Water

Ensure clean disposal of agriculture and animal production waste and residues (antimicrobial residues, pesticides) and safe transportation

15. Life on Land

Promote new technologies for agriculture practices to protect and restore soil, landscape, forests, and biodiversity

16. Peace, Justice, and Strong Institutions

Support the commitment to peaceful negotiation and land conflicts

17. Partnerships for Global development

Strengthen the holistic vison of One Health approach with transdisciplinary work at all levels, from local to global

The UN’s Sustainable Development Goals agenda provides a perspective on the importance of the One Health approach to ensuring good health for all and reducing extreme poverty and hunger, among other goals. Box 11 provides an overview of possible applications in the pursuit of the 17 goals.

In the declaration of the last G20 Summit hold in Argentina in December of 2018 (G20, 2018), it was encouraged the activities of WHO, together with all relevant actors, to develop an action plan for implementation of health‐related aspects of SDGs by 2030. Also was commend the progress made by the international community in developing and implementing National and Regional Action Plans on Anti‐Microbial Resistance (AMR) based on One‐Health approach and the need for further multisectoral action to reduce the spread of AMR. In the same paraph of the declaration it was mentioned the needs to continue to strengthen core capacities required by International Health Regulations (WHO IHR, 2008) for prevention, detection and response to public health emergencies. This health paragraph in the G20 declaration summarized several of the topics presented in this chapter, demonstrating the importance of the One Health approach for the current world.

Exclusion criteria	Mentioned “One Health” but most of the content was not related to One Health
	Not a review article
Categorization	History: articles mainly focusing on history (general history or region-specific history of One Health)
	Concept: articles mainly focusing on explaining the concept of One Health (comparing different concepts)
	Training: articles mainly focusing on One Health–related training in academic institutions or other places
	Research: articles with quantitative analysis including statistical or mathematical approach, or with situation analysis
	Intervention: articles describing or evaluating interventions (short-term, long-term)
	Advocacy: articles supporting application of the One Health concept in a qualitative way

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Article contents

“One Health” From Concept to Application in the Global World

“One Health” From Concept to Application in the Global World

Summary

Keywords

Subjects

Why the “One Health” Approach Is Important

Demographics

Why Demographics Matter in the One Health Approach

Urbanization

Why Urbanization Matters in the One Health Approach

Poverty and Income Equality

Why Poverty Matters in the One Health Approach

Box 1. United Nations Sustainable Development Goals

Migration and Displacement

Why Migration and Population Displacement Matter in the One Health Approach

Infectious Hazards and Epidemics

Why Infectious Hazards and Epidemics Matter in the One Health Approach

Box 2. International Health Regulations

Trade, Tourism, and the Global Economy

Why Trade, Tourism, and Global Economy Matter in the One Health Approach

Climate Change

Why Climate Change Matters in the One Health Approach

History of an Integrated One Health Concept

Box 3. One Health Meetings

The Concept

Box 4. Leptospirosis as an Example of Possible Application of the Operational Concept of One Health

Box 5. Avian Influenza (H5N1) as an Example of Possible Application of the Operational Concept of One Health

Box 6. Multidisciplinarity, Interdisciplinarity, and Transdisciplinarity Defined

Global Applications Using the One Health Concept

Box 7. Research Methodology: One Health in Peer-Reviewed Journals

Table 1. Articles Found in the Scoping Review on One Health, by Category and Year of Publication

Health Professionals and One Health

Expectations for One Health Professionals

Application of the One Health Concept in Research

Application of the One Health Concept in Advocacy and Interventions

Box 8. Integration Between Health and Agriculture in the Preparedness Plans in Latin America

Box 9. Rabies as an Example of Possible Application of the Operational Concept of One Health

Application of the One Health Concept in Antimicrobial Resistance

Box 10. Global AMR Initiatives

Conclusion

Box 11. United Nations Sustainable Development Goals and How They Can Be Supported by the One Health Approach

Acknowledgments

References

Notes

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