Wikipedia Deep Dive

One Health

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The Virus Doesn't Care What Species You Are

Here's something that should unsettle you: the deadliest pandemics in human history didn't start in humans. The Black Death came from fleas on rats. The 1918 influenza pandemic jumped from birds. HIV crossed over from chimpanzees. And the virus behind COVID-19 almost certainly emerged from bats, possibly through an intermediate animal host.

This isn't coincidence. It's biology.

Roughly seventy-five percent of emerging infectious diseases in humans are zoonotic—meaning they originate in animals before making the leap to people. We share our planet with millions of other species, breathe the same air, drink from the same water sources, and have immune systems built from remarkably similar biological blueprints. The boundary between "animal disease" and "human disease" is largely a fiction we've invented for administrative convenience.

This realization gave birth to a movement called One Health—an approach that sounds almost absurdly obvious once you hear it: human health, animal health, and environmental health are so deeply interconnected that you cannot effectively address any one of them in isolation.

When a Pathologist Made the Connection

The intellectual roots of One Health stretch back to nineteenth-century Germany, to a physician named Rudolf Virchow. Known today as the father of cellular pathology—the study of disease at the level of individual cells—Virchow was among the first to recognize that the wall between human and veterinary medicine was artificial. He studied parasites that infected both pigs and humans, and he coined the term "zoonosis" to describe diseases that jump between species.

One of Virchow's students was William Osler, a Canadian physician who would go on to become one of the founding professors at Johns Hopkins Hospital and is often called the father of modern medicine. Medical lore credits Osler with coining the term "One Medicine," though historians have never found direct evidence of this in his writings. Whether or not he used those exact words, the idea was clearly in the air.

But it took another century for the concept to crystallize into something actionable.

A Veterinarian Sees the Whole Picture

In the 1960s, a veterinarian named Calvin Schwabe was working at the University of California, Davis. Schwabe had trained in both veterinary medicine and public health—an unusual combination that gave him a peculiar vantage point. He could see what specialists in each field often missed: that the problems they were trying to solve were fundamentally the same problems.

In 1964, Schwabe published a veterinary textbook that introduced the term "One Medicine." His argument was straightforward. Humans are animals. We share evolutionary ancestry, similar organ systems, and susceptibility to many of the same pathogens. A virus doesn't consult a medical specialty directory before deciding whom to infect. Why, then, were doctors and veterinarians working in such complete isolation from each other?

Schwabe established a department at the University of California, Davis specifically designed to bridge this gap. He spent the next decade developing his ideas, publishing a fuller articulation of One Medicine in 1976. Today, UC Davis maintains a One Health Institute that continues his work.

But ideas don't become movements until crisis makes them urgent.

The Bird Flu That Changed Everything

In the early 2000s, a strain of influenza virus called H5N1 began spreading through poultry flocks in Asia with terrifying efficiency. The virus killed birds rapidly and could sometimes jump to humans who had close contact with infected poultry. When it did make that jump, it was often fatal—killing roughly sixty percent of confirmed human cases.

Sixty percent. For comparison, the 1918 influenza pandemic—which killed somewhere between fifty and one hundred million people—had a fatality rate of around two to three percent.

H5N1 didn't become a human pandemic, primarily because it couldn't spread efficiently from person to person. But the world had glimpsed what might happen if a similar virus evolved that capability. The question wasn't whether another pandemic would come. It was when, and whether we'd be ready.

This fear catalyzed action. In 2004, the Wildlife Conservation Society convened a conference at Rockefeller University in New York called "One World, One Health." The gathering produced the Manhattan Principles—twelve recommendations for a unified approach to preventing epidemic diseases. These principles emphasized the links between human, animal, and environmental health, and called for interdisciplinary collaboration in research, education, and policy.

By 2006, the American Veterinary Medical Association had established a One Health Initiative Task Force. In 2007, the American Medical Association passed a resolution urging partnerships between veterinary and human medical organizations. The same year, international health authorities recommended a One Health approach for responding to global disease outbreaks.

The Organizations Get On Board

In 2008, a coalition of major international organizations came together to formalize the approach. The Food and Agriculture Organization of the United Nations (known as FAO), the World Health Organization (WHO), and the World Organisation for Animal Health (then called OIE, now WOAH) joined with UNICEF, the World Bank, and the United Nations System Influenza Coordination to produce a strategic framework for reducing the risks of infectious diseases at what they called "the animal-human-ecosystems interface."

That's a mouthful of bureaucratic language, but the core idea was simple: stop treating human medicine, veterinary medicine, and environmental science as separate kingdoms with separate budgets and separate priorities. Build systems that let them talk to each other.

The movement continued to gain institutional momentum. In 2009, the Centers for Disease Control and Prevention (CDC) created a dedicated One Health Office—the first such office in any United States federal agency. That same year, the One Health Commission was chartered in Washington as a nonprofit organization dedicated to connecting professionals across human, animal, and environmental health.

In 2016, these organizations designated November 3rd as International One Health Day.

What Does One Health Actually Mean?

Definitions of One Health vary slightly depending on who's doing the defining, but they all circle around the same core insight. The most comprehensive definition comes from the One Health High Level Expert Panel, an independent advisory group:

"One Health is an integrated, unifying approach that aims to sustainably balance and optimize the health of humans, animals, plants and ecosystems. It recognizes the health of humans, domestic and wild animals, plants and the wider environment (including ecosystems) are closely linked and interdependent. The approach mobilizes multiple sectors, disciplines and communities at varying levels of society to work together to foster well-being and tackle threats to health and ecosystems, while addressing the collective need for clean water, energy and air, safe and nutritious food, taking action on climate change, and contributing to sustainable development."

That's the formal version. Here's the practical version: when a new disease emerges, you don't just send doctors to treat the sick. You send veterinarians to study the animal reservoir. You send ecologists to understand what environmental changes might have triggered the spillover. You send epidemiologists who can trace the chain of transmission across species. And crucially, you have these people talking to each other from day one, not years later when academic papers finally get published.

The Problem of Antimicrobial Resistance

One Health isn't only about pandemics. It also addresses one of the most insidious slow-motion crises in modern medicine: antimicrobial resistance.

Here's the problem. Antibiotics don't just get used in human hospitals. They get used—often overused—in agriculture. Farmers administer antibiotics to livestock not only to treat infections but to promote growth and compensate for crowded, unsanitary conditions. This creates perfect breeding grounds for resistant bacteria.

Those resistant bacteria don't stay on the farm. They spread through the food supply, through water contaminated with agricultural runoff, through farm workers who carry them home. A resistant strain that evolves in a pig can end up in a human patient who has never set foot on a farm.

You cannot solve this problem by focusing only on hospital antibiotic stewardship. You cannot solve it by focusing only on agricultural practices. You have to address both simultaneously—which requires the kind of cross-sector collaboration that One Health advocates.

The Society of Infectious Diseases Pharmacists (SIDP), an organization of pharmacists and other health professionals focused on infectious diseases, has made One Health principles central to their mission. They maintain educational resources explaining how antimicrobial stewardship—the effort to use antibiotics judiciously—must extend beyond human medicine into veterinary and agricultural contexts.

The Environment Gets a Seat at the Table

For years, One Health primarily meant collaboration between human doctors and veterinarians. The environment was acknowledged as important, but environmental scientists and ecologists were often afterthoughts in these discussions.

That changed in 2021. The three major partner organizations—FAO, WHO, and WOAH—had been working together as a "Tripartite" for over a decade. In February 2021, they invited the United Nations Environment Programme (UNEP) to join them. The Tripartite became the Quadripartite.

This wasn't just a bureaucratic reshuffling. It reflected a growing recognition that environmental degradation—deforestation, habitat destruction, climate change, biodiversity loss—is a primary driver of disease emergence. When humans push into previously wild areas, when we fragment ecosystems and force wildlife into closer contact with livestock and people, we create opportunities for pathogens to jump species.

The equation is straightforward: healthier ecosystems mean fewer disease spillovers. Environmental protection is disease prevention.

Making It Work in Practice

Theory is one thing. Making One Health work in the real world is another matter entirely.

Consider the CDC's One Health Zoonotic Disease Prioritization process. The CDC holds workshops with countries around the world to help them identify which zoonotic diseases pose the greatest threats and develop action plans to address them. Each workshop involves three to six facilitators representing human, animal, and environmental health sectors. Up to twelve voting members represent various government agencies—health ministries, agriculture departments, wildlife services. Another ten to fifteen advisors come from international organizations, academic institutions, and nongovernmental organizations.

Preparing for a single workshop takes months. Facilitators must be trained. Resources must be gathered. Participants must be identified. Information about zoonotic diseases in the region must be compiled and reviewed.

Countries that have completed this process include Pakistan, Tanzania, Thailand, Uzbekistan, and China. The diseases most commonly flagged as priorities include rabies, brucellosis, influenza, Ebola virus, and Rift Valley fever.

This is slow, painstaking work. It requires getting government agencies that don't normally talk to each other to sit in the same room and make decisions together. It requires reconciling different professional cultures, different vocabularies, different assumptions about what matters most.

The Book That Made One Health Popular

Academic papers and international frameworks don't usually capture the public imagination. Books sometimes do.

In 2012, Barbara Natterson-Horowitz, a cardiologist who consulted at the Los Angeles Zoo, and Kathryn Bowers, a science journalist, published a book called "Zoobiquity." The title was a neologism—a new word—meant to capture the ubiquity of medical parallels between humans and other animals.

The book drew vivid connections. Horses get eating disorders. Koalas contract chlamydia. Birds experience heart attacks from stress. Natterson-Horowitz and Bowers argued that physicians could learn enormously from veterinarians—and that the arbitrary separation between human and animal medicine was actively harming our ability to understand and treat disease.

Zoobiquity became a New York Times bestseller. Critics praised it as accessible and entertaining, though some academics complained that it lacked depth and failed to grapple with the genuine complexities of comparing species that have evolved quite differently.

Regardless of its scholarly limitations, the book did something important: it introduced One Health ideas to readers who would never pick up a WHO policy document.

The Political Dimension

One Health has also entered the realm of legislation. In 2019, Senator Tina Smith of Minnesota and Representative Kurt Schrader of Oregon introduced the Advancing Emergency Preparedness Through One Health Act into the United States Congress. The bipartisan bill would require the Department of Health and Human Services, the Department of Agriculture, and other federal agencies to develop a coordinated One Health Framework for responding to zoonotic diseases.

The bill didn't pass in 2019. Senator Smith reintroduced it in 2021 with Senator Todd Young of Indiana as a cosponsor.

Legislative efforts like this matter because One Health ultimately requires institutional change. It's not enough for individual scientists to believe in interdisciplinary collaboration. The agencies they work for must be structured to enable that collaboration—with shared funding streams, joint appointments, coordinated surveillance systems, and legal frameworks that don't trap information in bureaucratic silos.

The Network of Organizations

Today, One Health is supported by a sprawling network of organizations at local, national, and international levels.

The One Health Commission, headquartered in the Research Triangle region of North Carolina, maintains a directory called "Who's Who in One Health" cataloging organizations worldwide that are advancing One Health principles. It also runs a global listserv connecting practitioners and maintains a One Health Library of resources.

The One Health Initiative is a broader movement coordinating among organizations including the American Veterinary Medical Association, the American Medical Association, the CDC, the United States Department of Agriculture, and Vétérinaires sans Frontières (Veterinarians Without Borders).

The One Health Platform, managed by a board that includes virologist Ab Osterhaus, serves as a scientific reference network connecting researchers working on zoonotic diseases and antimicrobial resistance. It organized the World One Health Congress annually from 2015 through 2020, with subsequent meetings hosted by institutions like the SingHealth Duke-NUS Global Health Institute in Singapore.

Why It Matters Now More Than Ever

If One Health ideas had been more deeply embedded in global health systems, would we have responded better to COVID-19? It's impossible to know for certain, but there are reasons to think the answer might be yes.

Early detection of novel pathogens requires surveillance systems that monitor animal populations—especially wildlife—for emerging threats. Understanding transmission dynamics requires collaboration between wildlife biologists, veterinarians, and epidemiologists. Developing countermeasures requires pharmaceutical research that draws on both human and veterinary medicine.

COVID-19 emerged from the interface between wild animals, domestic animals, and humans. That interface is exactly where One Health focuses its attention.

And that interface is expanding. As human populations grow, as we convert wild lands to agriculture, as climate change pushes species into new territories, the opportunities for pathogens to spill over from animals to humans multiply. The basic dynamics that produced COVID-19 haven't changed. If anything, they're intensifying.

The Same Drugs, The Same Problems

Here's something that might surprise you: many of the drugs used to treat infections in animals are structurally identical—or very similar—to drugs used in humans. This isn't coincidence. We share so much fundamental biology with other mammals that the same molecules often work in both.

This creates both opportunities and problems. The opportunity is that insights from veterinary medicine can inform human medicine, and vice versa. A drug that works in dogs might work in people. A treatment protocol developed for livestock might be adaptable to human patients.

The problem is that overuse of these drugs in any context—human hospitals, veterinary clinics, agricultural operations—accelerates resistance that affects all contexts. When we pump antibiotics into cattle to make them grow faster, we're eroding the effectiveness of those same antibiotics for treating sick children.

This is why One Health advocates insist that antimicrobial stewardship must be a coordinated, cross-sector effort. You cannot preserve the effectiveness of these drugs by managing only one piece of the system.

The Road Ahead

One Health has come a long way from Rudolf Virchow's nineteenth-century observations about parasites in pigs. It has institutional support from the world's major health organizations. It has academic programs, research institutes, and dedicated journals. It has policy frameworks and legislative proposals.

But transforming how institutions actually operate is slow, difficult work. Government agencies guard their turf. Professional cultures resist change. Funding streams remain siloed. The urgent crises of the moment—the outbreak already happening—crowd out investment in the surveillance and prevention systems that might stop the next one.

What COVID-19 demonstrated, more vividly than any previous crisis, is the cost of these institutional failures. The virus that began in an animal somewhere in China became a global catastrophe because we lacked the systems to detect it early, contain it at source, and coordinate a coherent response.

One Health won't prevent the next pandemic by itself. But a world that takes One Health seriously—that actually builds the collaborative systems, the shared surveillance networks, the cross-disciplinary research programs—would be far better equipped to face whatever comes next.

The virus doesn't care what species you are. Our health systems should stop pretending otherwise.