Loading field map
The central question that drives the One Health subfield is deceptively simple: how should we understand and manage the health of humans, animals, and the environment together? For more than two centuries, veterinarians, physicians, and public health officials have offered different answers, each shaped by the practical pressures of its era. The result is a sequence of four major frameworks—One Medicine, Veterinary Public Health, Herd Health Management, and One Health—that alternately broadened, narrowed, and reintegrated the scope of interconnected health. Their history reveals not a steady march toward consensus but a series of deliberate choices about what counts as relevant, who should collaborate, and which methods are trustworthy.
The earliest framework, One Medicine, emerged in the nineteenth century as a direct outgrowth of comparative pathology. Pioneers such as Rudolf Virchow and William Osler recognized that many diseases—especially zoonoses—could not be understood by studying humans or animals in isolation. One Medicine argued that human and animal health were fundamentally the same discipline, differing only in species. Its method was comparative: pathologists examined lesions across species to trace the natural history of infections, and clinicians shared insights across the human–animal divide. This framework was intellectually ambitious, but it lacked a dedicated institutional home. It remained a scholarly ideal rather than a practical program, and by the early twentieth century its broad vision began to fragment under the weight of specialization.
As veterinary medicine professionalized, two narrower frameworks emerged from the One Medicine tradition, each addressing a different practical demand. Veterinary Public Health, formalized around 1900, focused on protecting human populations from animal-borne threats. Its core activities—meat inspection, zoonotic disease surveillance, and food safety regulation—were driven by the rise of industrial food production and the germ theory of disease. Unlike One Medicine, which treated human and animal health as symmetrical, Veterinary Public Health was explicitly anthropocentric: animals mattered primarily as sources of risk or benefit to people. Its methods were epidemiological and regulatory, and its institutional home was the state public health apparatus.
At roughly the same time, but with a different emphasis, Herd Health Management took shape in the mid-twentieth century as livestock farming intensified. Where Veterinary Public Health looked outward to human populations, Herd Health Management looked inward to the production herd. Its central insight was that disease in a herd is a management problem, not just a medical one. Veterinarians working within this framework developed population-level protocols for nutrition, housing, vaccination, and biosecurity, treating the herd as the unit of analysis rather than the individual animal. This framework coexisted with Veterinary Public Health but rarely overlapped with it: one focused on human protection, the other on agricultural productivity. Both were narrower than One Medicine, and neither gave serious attention to environmental health or to the health of wildlife outside production systems.
By the late twentieth century, the limitations of these narrowed frameworks became apparent. Emerging infectious diseases such as Ebola, SARS, and avian influenza revealed that human and animal health were linked through ecological processes that neither Veterinary Public Health nor Herd Health Management could address. Meanwhile, environmental degradation—climate change, deforestation, pollution—was reshaping disease transmission in ways that demanded a broader perspective. In 1964, the epidemiologist Calvin Schwabe revived the term "One Medicine" to call for renewed collaboration between human and veterinary medicine, but the framework that eventually took hold went further.
The modern One Health framework crystallized in the early 2000s, most visibly at the 2004 conference "One World, One Health" organized by the Wildlife Conservation Society. The resulting Manhattan Principles explicitly added environmental health as a third pillar, arguing that human, animal, and ecosystem health are interdependent. One Health did not simply revive One Medicine; it transformed it by insisting that environmental factors—habitat loss, biodiversity, climate—are not external conditions but integral components of health systems. Its methods are interdisciplinary, drawing on epidemiology, ecology, microbiology, and social science, and its institutional support comes from organizations such as the World Health Organization, the Food and Agriculture Organization, and the World Organisation for Animal Health.
These four frameworks differ systematically in scope, method, and unit of analysis. One Medicine was broad but vague, relying on comparative pathology and individual case observation. Veterinary Public Health narrowed the scope to zoonotic and foodborne risks, using epidemiological surveillance and regulatory enforcement. Herd Health Management narrowed further to production populations, using management protocols and economic analysis. One Health broadens again to include all species and ecosystems, using systems thinking and cross-sectoral collaboration.
Their relationships are not simply linear. Veterinary Public Health and Herd Health Management did not replace One Medicine; they absorbed parts of it while leaving others behind. One Medicine's comparative vision survived in the training of veterinary pathologists, but its integrative ambition was dormant until One Health revived it. Today, Veterinary Public Health and Herd Health Management remain active frameworks, each with its own institutional base and practical domain. Veterinary Public Health continues to lead in food safety and zoonotic disease control, while Herd Health Management dominates production animal medicine. One Health, however, has become the leading framework for addressing complex, multi-species health challenges such as pandemic preparedness, antimicrobial resistance, and climate-sensitive diseases.
What do the leading frameworks agree on today? There is broad consensus that human, animal, and environmental health are connected and that collaboration across disciplines is necessary. Most practitioners accept that a purely biomedical approach is insufficient for problems like emerging zoonoses or food system sustainability. Where they disagree is on the practical implications. Some argue that One Health should remain a collaborative ideal, leaving Veterinary Public Health and Herd Health Management to handle their traditional domains. Others insist that One Health requires a fundamental restructuring of institutions, funding, and training—a shift that would challenge the existing division of labor. The tension between integration and specialization remains unresolved, and it is this very tension that keeps the subfield dynamic.
One Health is not a finished framework but an evolving response to the question that has always driven this field: how to care for health across species and ecosystems without losing sight of the specific needs of each. The history of its four frameworks shows that every answer creates new gaps, and every narrowing invites a later broadening.