We live in a world that is rapidly changing, complex and progressively more interconnected. The convergence of people, animals and our environment has created a new dynamic - one in which the health of each group is now profoundly and inextricably linked and elaborately connected.

Inherent in this new dynamic is the changing interface between people and animals including animal products. The human-animal interface is accelerating, expanding and becoming increasingly more consequential. Over the last 3 decades, approximately 75% of new human infectious diseases are zoonotic.¹

Increased global trade and travel, urbanization, climate change, microbial adaptation and the rapid expansion of agricultural operations to meet the growing worldwide need for food and energy have all contributed to disease emergence, reemergence and spread. The great convergence of people, animals and the environment and the resultant health threats to all three demands a new mindset to confront infectious diseases in our interconnected world. Scientists, health professionals and practitioners must now move beyond the confines of their own disciplines and explore new models of collaboration. International health organizations and government agencies must also build cooperative relationships, especially across the domains and public and animal health. The concept of One Health is, more and more, being recognized as a transformational mindset to ensure more integrated and holistic approaches to confront our health threats.

In addition, the global population has now exceeded 7 billion people and an estimated 25–30 billion food animals were produced to help feed this population and meet their growing demand for protein from animal sources.² The result is a phenomenal global food system that is both a major agricultural and business accomplishment and an unparalleled challenge that is creating major societal issues that, to some extent, threaten human, animal and environmental health. The application of a One Health model, where potential solutions are viewed and delivered more holistically and with an emphasis on prevention, is a compelling and timely strategy.

Each year, approximately 15 million human deaths and countless animal deaths worldwide are caused by infectious diseases. These diseases posing substantial global challenges and the threat to the health of people, animals and the environment have become a major millennial concern. The domains of people, animals and their products and our ecosystems have converged globally, and have created an unprecedented dynamic of interactions at the interface of these three domains. Clearly, our microbial world is rapidly changing and new movements of microbes and novel exposures at the human-animal interface are now the norm and represent a driving force in the convergence of people and animals. This is increasingly the case in the developing world where there is concern about the capabilities of their public and animal health infrastructures.

One Health is the collaborative effort of multiple disciplines - working locally, nationally and globally to attain optimal health for people, animals and our environment.³ The scale and complexity of health issues demands that scientists, researchers and others move beyond the confines of their own disciplines, professions and mindsets, and explore new organizational models of team science. The One Health concept embodies this declaration. The scope of One Health is impressive, broad and growing. Much of the recent focus of One Health has been limited to emerging infectious diseases; yet, the concept clearly embraces environmental and ecosystem health, social sciences, ecology, noninfectious diseases and chronic diseases, wildlife, land use, antimicrobial resistance, biodiversity and much more. While these components are appreciated within our understanding of the broad dimensions of health, they also add to the complexity of One Health and can add to the difficulty in implementing strategies, building effective coalitions and mobilizing scientific communities who embrace One Health, yet who have been trained and think in a much narrower scope and scale. Although there may be not a single definition of One Health, there is broad consensus that a new framework for addressing contemporary disease problems, as well as preventing new emerging or reemerging disease, is essential rather than the alternative of constantly responding to them reactively as we have done in the past.

The world population has a growth rate of 1.2% per year and the next century will represent a period of exponential growth. There is also a significant demographic fault line between the population growth in developed versus developing countries. Approximately 90% of the world's population growth is occurring in the developing countries of the world. In addition, almost 1 billion people live in peri-urban or slum settings in the developing world's largest cities and these sites are where the most rapid growth in our human populations will continue.

We are concurrently observing a relative increase in wealth in the developing world, and as per capita incomes rise, people eat more calories and consume different products, especially involving a building demand for meat and protein from animal sources. Today, 3–4 billion people consume very little meat, but will consume more, should incomes increase. Thus, a new agricultural phenomenon is emerging - The Livestock Revolution. With relative increases in wealth and technological advances in livestock and poultry production, global increases in production and consumption of livestock products are assured. The FAO estimates that there will be a demand for a 50% increase for animal proteins in the next 1–2 decades.⁴ Thus, the entire global food system will shift towards more intensive, specialized and integrated production systems and much of the production will progressively move to the developing world.

Concurrently, there is unprecedented immigration and movement of people worldwide. Unique diasporas have emerged and there are large numbers of immune-compromised individuals dispersed throughout the U.S. and global populations who are especially susceptible to infections including food- and water-borne illnesses. In many countries, the population of seniors is one of the fastest growing cohorts and may become especially susceptible to infectious diseases.

There is also a disconnect between global commerce and the remarkable movement of billions of pounds of food in trade channels and the assurance of safe food and public health. This has created a significant gap between the rapidly growing global food systems, and the development and investment in public health and animal health infrastructures needed to address potential threats. The 21st century has created a great mixing bowl of people, animals and animal products and a group of difficult challenges, including the protection and safety of our food that demands a transformation of thought and actions to address these contemporary challenges. Threats to our health and wellbeing and threats to animal and environmental health are under increasing pressure. A holistic and integrated approach considering these domains in a One Health strategy is both logical and essential to further success.

Today, microbes can traverse the globe faster than their incubation period; our great convergence offers unique opportunities for them to cross species lines, become resistant to antimicrobial agents, adapt, change and find new niches, and emerging and reemerging diseases result. Our current era of emerging infections is continuing and the pace of emergence is accelerated with changing ecosystems, risky human behavior, poverty, travel, trade, globalization, population growth and our interconnectiveness. Food and water, as a potential vehicle for disease transmission, is embedded in this complex system; food and water safety has taken on a growing importance and has become a critical public health imperative.

According to Jared Diamond, in his book "Guns, Germs and Steel," diseases such as measles, smallpox, influenza and tuberculosis likely evolved from animal diseases as the first group of zoonotic diseases. The advent of agriculture and the domestication of animal approximately 8–10,000 years ago were drivers of a new human-animal interface and the first era of emerging zoonotic diseases. Although animal agriculture is much more sophisticated today, it is also growing more intensified and complex. Domestication has resulted in the development of new and more efficient food-animal species and the human-animal interface has accelerated and multiplied through the globalization of our food system and has created the potential exposure of billions of people to potential pathogens. As our food-animal production and ecosystems continue to change to produce more and more, microbes have been given further opportunities to adapt and find new niches. Transboundary diseases have again emerged at an alarming rate, suggesting that our new era of disease emergence has a troubling similarity to the past era that was created 8–10,000 years ago.

Dr. Gro Brundtland, former Director of the World Health Organization, stated that "In a modern world, bacteria and viruses travel almost as fast as money. With globalization, a single microbial sea washes over all humankind and there are no health sanctions." In actuality, that microbial sea washes not just over all humankind, but also across our animal and environmental domains. This dynamic exposes and connects the human, animal and environmental domains in ways never previously experienced. Positive and negative actions and impacts in one domain, now, may significantly impact the others, and solutions to address threats in any single domain may have multiplier effects in the others. This is the essence of One Health and represents a unique mindset and new competencies that are uniquely emphasized in veterinary medicine. Perhaps, our greatest challenge today may be our ability to reconcile the changes and challenges of our global convergence with our traditional thinking and habitual ways of working.

Patterns of thought of a previous area may not be useful to address current problems. Because problems are part of the society that creates them, future solutions and actions must be based in that society. We can no longer focus on a single domain of health or a single intervention; we now must be open to new ways of thinking and be receptive to new ideas and directions that match our challenging times. The status quo must be replaced by a new transdisciplinarity and a new collective understanding of disease ecology characterized by a One Health mindset and approach. A One Health emergent community of practice now exists where new views, approaches and knowledge inform each other and these lessons learned can be adopted by others. One Health, although not new, is certainly a renewed field of inquiry and transdisciplinary thinking.

The convergence of people, animals and our environment has created a new dynamic in which the health of each domain is inextricably interconnected. The challenges associated with this new reality are demanding, profound, and unprecedented. This remarkable convergence is a critical factor in disease emergence and there is nothing on the horizon to suggest that this dynamic will be altered or abated. Working successfully to address these threats will require new thinking, changing partnerships and shifting our emphasis "upstream" closer to the origin of pathogens in other domains. Adopting a One Health paradigm holds great promise, but also represents a new mindset that will be disruptive to the status quo. Thus, old systems, habitual thinking and working with old modes of inquiry that are sharply divided among diverse cultures and interests and which compete for resources remain as future challenges.

While we recognize the immense challenges that we face, our current reality also represents an unprecedented opportunity for veterinary medicine. The veterinary profession is uniquely positioned to lead a One Health renaissance and it has an opportunity to be more relevant than any other time in our history. The success of veterinary medicine will center on its ability to fulfill its social contract and meet the changing needs and demands of society. To achieve this contract, the profession must collaborate beyond its traditional boundaries, proclaim and demonstrate its relevance and lead the reemergence of a One Health mindset that can be the basis for veterinary medicine to rethink, recreate and revitalize itself. It has been said that the greatest optimism about the future is that it can still be created - this is the extraordinary calling of veterinary medicine and is the basis for its transformation.

References

1.  Taylor LH, Latham SM, Woolhouse ME. Risk factors for human disease emergence. Phil Trans R Soc London. 2001;B355:983–989.

2.  Food and Agriculture Organization. Agriculture and an Animal Feed Industry. 2006. Business Meeting Presentation.

3.  King LJ, et al. One Health initiative task force report. J Am Vet Med Assoc. 2008;233(2):259–261.

4.  Delgado C, Rosegrant M, Steinfeld H, Ehui S, and Courbois C. Livestock to 2020: the next food revolution. FAO Discussion Paper. 1999;28:1–13.