Three out of every five known human infectious diseases originated in animals. Three out of every four newly emerging infectious diseases do. SARS came from bats via civets, COVID-19 from bats with debated intermediate hosts, MERS from bats via camels, Ebola from bats with bushmeat as a likely contact route, H5N1 from waterfowl through poultry into mammals. The pattern is so consistent that any framework for outbreak prevention that treats human medicine and animal medicine as separate disciplines is missing the place most outbreaks actually start.
One Health is the response. It is the operating principle that human health, animal health, and environmental health are inseparable, and that surveillance, prevention, and response have to span all three. The framework has been formalized into a quadripartite agreement among WHO, the World Organisation for Animal Health (WOAH), the Food and Agriculture Organization (FAO), and the UN Environment Programme (UNEP). It is also more often referenced than implemented. This post covers what One Health actually means in practice, where it works, and where the seams show. It is part of pandemic preparedness 101.
Key Takeaways
- 60 percent of known human infectious diseases are zoonotic; an estimated 75 percent of newly emerging diseases are zoonotic.
- One Health treats human, animal, and environmental health as a single integrated system. Surveillance, prevention, and response coordinate across the three domains.
- The Quadripartite (WHO, WOAH, FAO, UNEP) coordinates global One Health policy. Field implementation runs through national programs, university networks, and NGOs.
- Three areas where One Health has produced measurable wins: avian influenza surveillance and early warning, rabies elimination through dog vaccination, and reduction of antimicrobial use in livestock.
- The framework's biggest gaps are funding, jurisdictional coordination at country level, and the disconnect between human-focused public health and veterinary or wildlife health budgets.
What is One Health?
One Health is an integrated, unifying approach that recognizes that the health of people, animals, and ecosystems are closely connected and interdependent. The framework formalizes what zoonotic disease research has been showing for decades: that new pathogens emerge at the human-animal-environment interface, and that interventions limited to one domain repeatedly fail to control them.
In operational terms, One Health asks veterinary, public health, and environmental authorities to share data, coordinate responses, and design joint surveillance systems. A One Health-aligned country program might link laboratory networks across human, livestock, and wildlife testing, share outbreak signals between agriculture and health ministries, and build emergency response plans that cross those boundaries before a crisis. The framework is intentionally broad because the problems it addresses are.
Why did the One Health framework emerge?
Three drivers pushed One Health from niche concept to formal policy through the 2000s and 2010s. The first was the SARS outbreak in 2003, which made it visceral that a wild-animal market and an international travel hub could combine into a global health emergency in weeks. The second was repeated H5N1 outbreaks across poultry and the watchful concern that the virus would adapt to humans (it has, repeatedly, in small clusters). The third was COVID-19, which sharpened every prior argument about preparedness gaps.
Antimicrobial resistance is the slower-moving driver that makes One Health unavoidable. About 70 percent of antibiotics globally are used in animal agriculture rather than human medicine. Resistant bacteria emerging in livestock cross over to humans through food, environment, and direct contact. You cannot solve antimicrobial resistance by reforming hospital prescribing while leaving farm use untouched, and the framework that explicitly says so is One Health.
What does One Health look like in real outbreaks?
Three case studies show the framework working at different scales.
Avian influenza surveillance
Global avian flu surveillance is the most mature One Health application. Wild bird sampling (run by FAO and partner programs), poultry surveillance (run by national veterinary services and WOAH), and human surveillance (WHO GISRS) feed into a single picture of where dangerous H5 strains are circulating. The 2024 detection of H5N1 in US dairy cattle was caught quickly because the surveillance infrastructure was in place to recognize the same clade was crossing into a new mammalian host.
Rabies elimination
Rabies kills 59,000 people a year and 99 percent of those cases come from dogs. Mass dog vaccination plus stray dog management (a One Health approach combining veterinary public health, animal welfare, and human medicine) has eliminated dog-mediated human rabies in much of Latin America and is the WHO target for global elimination by 2030. Treating rabies as a human disease alone, by relying only on post-exposure prophylaxis, is more expensive and less effective. See rabies prevention and PEP timing for the human-medicine companion to this work.
Reducing antimicrobial use in livestock
The Netherlands cut total antibiotic use in livestock by more than 60 percent between 2009 and 2020 through coordinated veterinary, agriculture, and public health policy. Resistance rates in human and animal isolates fell in parallel. The intervention worked because all three sectors were aligned. Programs that try to reduce hospital prescribing without addressing farm use repeatedly stall.
Who runs One Health globally?
The Quadripartite is the formal governance structure. Each member contributes:
- WHO: human health surveillance, IHR, pandemic preparedness, vaccine policy
- WOAH (World Organisation for Animal Health): animal health standards, livestock disease reporting, veterinary services capacity
- FAO (Food and Agriculture Organization): food security, livestock production, antimicrobial use in agriculture
- UNEP (UN Environment Programme): ecosystem health, biodiversity, climate, wildlife trade
The four agencies signed a memorandum of understanding in 2022 that formalizes joint priorities, including the One Health Joint Plan of Action 2022 to 2026. Below the global level, regional bodies (Africa CDC, ECDC, ASEAN) and national programs implement. A handful of universities and consortia (the EcoHealth Alliance, the One Health Commission, USAID PREDICT during 2009 to 2019) have run major field surveillance projects with mixed sustainability records.
Where does One Health break down?
The biggest barrier is funding. Public health budgets, veterinary services budgets, and environmental ministries report through different parts of national governments, with separate appropriation processes and limited joint authority. A surveillance system that requires coordinating three ministries with different funders and incentives is structurally fragile. The Quadripartite has no enforcement authority and limited operational budget; its work is convening, normative, and dependent on member-state implementation.
Workforce is the second barrier. There are far more human-medicine clinicians than veterinarians in most countries, and far more veterinarians than wildlife and ecosystem health specialists. Field epidemiology training programs that include all three are still scarce. The result is that One Health is over-represented in policy documents and under-represented in operational rosters. The third barrier is privatization of the relevant data: livestock industry data is often proprietary, and wildlife surveillance is often run by NGOs without long-term funding.
The framework still works where it has political support and stable funding. The countries with the most operational One Health programs (Denmark, Netherlands, Thailand, parts of East Africa supported by FAO and Africa CDC) consistently outperform comparable countries on rabies, AMR, and zoonotic surveillance metrics. The case for the framework is empirical, not just theoretical. See zoonotic diseases explained for the underlying disease-emergence picture.
FAQ
Is One Health the same as planetary health?
Related but distinct. One Health centers on the human-animal-environment interface as a system for managing infectious disease, AMR, and food safety. Planetary health is broader, framing all human health in terms of the limits of natural systems (climate, biodiversity, biogeochemical cycles). The two communities overlap heavily on personnel and citations but maintain separate institutional homes.
Does One Health include mental health?
Generally no, in operational practice. One Health is dominated by infectious disease, food safety, and antimicrobial resistance work. Some recent frameworks include occupational mental health for veterinarians, farmers, and wildlife workers, but the core agenda is biological-disease focused rather than the full breadth of human well-being.
How does One Health relate to climate change?
Climate change is increasingly recognized as a driver of disease emergence at the human-animal-environment interface. Range shifts in disease vectors (mosquitoes, ticks), changes in wildlife behavior and contact patterns, and increased flooding and storm frequency all push pathogens into new contexts. UNEP's role in the Quadripartite reflects this connection. See climate change and infectious disease for the disease-specific picture.
Why don't more countries implement One Health programs?
Coordination is hard, expensive, and politically thankless. The benefits of integrated surveillance and response are diffuse and long-term; the costs land on specific agency budgets in the next fiscal year. Without strong central authority and political will, ministries default to working in their own lanes. The countries that have built durable One Health programs typically did so under the pressure of a major outbreak (avian flu in Thailand, rabies in Mexico, BSE in the UK) that made the cost of inaction visible.
Can a single person practice One Health?
Yes, in the sense that a clinician asking a febrile patient about animal contact, a veterinarian thinking about zoonotic risks to farm workers, or a wildlife biologist sharing surveillance data with public health are all doing One Health at the individual level. The institutional version is harder. The interpersonal version is the foundation it has to sit on.