Foundations of One Health

One Health: Definition and Scope What is One Health? One Health is a collaborative, integrated approach to addressing health challenges by recognizing that human health, animal health, plant health, and environmental health are deeply interconnected. Rather than treating these as separate domains, One Health brings together experts from medicine, veterinary medicine, environmental science, and other disciplines to work locally, nationally, and globally toward optimal health outcomes for people, animals, and ecosystems. The fundamental insight behind One Health is simple but powerful: we cannot achieve sustainable human health while ignoring the health of animals and the environment around us. These systems are interdependent, and problems in one domain inevitably affect the others. Why One Health Emerged One Health developed as a direct response to scientific evidence showing how diseases move between species and affect multiple stakeholders simultaneously. Zoonotic diseases—illnesses that spread from animals to humans—demonstrated that health threats do not respect disciplinary boundaries. A disease outbreak in animal populations can quickly become a human pandemic. Similarly, environmental degradation affects both animal and human populations. This recognition forced the global health community to reconsider traditional siloed approaches to public health. The approach also acknowledges a basic biological reality: humans and animals share conserved physiology. This means we can often treat similar conditions in different species using structurally related or identical drugs. While this is medically useful, it also creates a critical responsibility—we must carefully manage how we use these drugs in both human and veterinary medicine. Unnecessary or excessive treatment in either domain can accelerate antimicrobial resistance, a problem that harms both humans and animals. One Health calls for coordination between sectors to prevent this shared threat. The Scope of One Health Traditional public health focused narrowly on human disease and health outcomes. One Health dramatically expands this scope by treating human health as one part of an integrated system that includes: Animal health — domestic livestock, companion animals, and wildlife Plant health — crops and natural vegetation Environmental health — water systems, air quality, soil integrity, and ecosystem function These domains are not separate concerns; they interact constantly and create feedback loops. Unhealthy ecosystems produce disease reservoirs. Sick animals transmit pathogens to humans. Poor human practices degrade environments. One Health asks professionals in all these areas to communicate and coordinate. The Quadripartite Partnership Recognizing that One Health requires institutional support, four major international organizations formalized a partnership to advance the approach. These organizations, collectively known as the Quadripartite, are: The Food and Agriculture Organization of the United Nations (FAO) — focuses on agriculture and food systems The World Health Organization (WHO) — coordinates global human health The World Organisation for Animal Health — addresses animal health and disease (formerly known as the OIE) The United Nations Environment Programme (UNEP) — manages environmental concerns Together, these organizations represent the major stakeholders affected by One Health issues and coordinate global efforts to address health threats that span multiple sectors. Historical Development of One Health Early Recognition of Human-Animal Health Connection The connection between human and animal health is not a modern discovery. In the 19th century, two influential physicians—Rudolf Virchow and William Osler—noted the relationship between animal health and human disease. Their observations laid philosophical groundwork for what would eventually become One Health, though the formal concept wouldn't emerge for over a century. <extrainfo> William Osler is traditionally credited with coining the term "One Medicine," though direct historical evidence for this attribution is limited. The term may have developed gradually from his earlier observations rather than being formally declared at a specific moment. </extrainfo> Formalizing "One Medicine": Calvin Schwabe The crucial turning point came in 1964 when veterinarian Calvin Schwabe published a textbook that introduced the term "One Medicine." Schwabe's work was revolutionary because it not only named the concept but actively called for genuine collaboration between physicians and veterinarians—two professions that had traditionally operated independently. Schwabe argued that neither profession could fully address health challenges without understanding the other's perspective and expertise. This formalization was essential. Before Schwabe, the idea existed in scattered observations; after Schwabe, it became a coherent framework that professionals could build upon. The Manhattan Principles (2004) The concept remained largely academic until 2004, when a pivotal conference titled "One World, One Health" took place in Manhattan. This conference brought together international experts and produced twelve foundational statements known as the Manhattan Principles. These principles defined a unified approach to preventing epidemic diseases and explicitly emphasized that interdisciplinary cooperation—across medicine, veterinary medicine, environmental science, and other fields—was essential to addressing modern health threats. The Manhattan Principles marked the transition from theoretical concept to practical framework. They provided the intellectual foundation for organizations to begin coordinating their efforts. Strategic Framework and Institutional Support (2008) Four years after Manhattan, the Food and Agriculture Organization, World Organisation for Animal Health, and World Health Organization created a formal strategic framework for reducing infectious disease risk at the animal-human-ecosystem interface. This framework operationalized One Health by identifying how organizations could actually work together to prevent diseases before they emerged. The One Health Initiative Beyond the Quadripartite, the One Health Initiative emerged as a supporting organization dedicated to promoting rapid knowledge exchange among animal, human, and environmental health professionals. The Initiative recognized that outbreaks move faster than traditional communication channels, so it focused on creating mechanisms for real-time information sharing. This improved the speed and effectiveness of outbreak responses by ensuring that relevant experts across sectors could quickly learn about emerging threats and coordinate responses. <extrainfo> The modern One Health framework continues to evolve as new threats emerge (such as COVID-19, which demonstrated the critical importance of understanding zoonotic disease dynamics) and as technology enables better real-time collaboration between previously siloed professionals. </extrainfo>