“One Health” needs ecology

The planet’s surface temperature has risen 2.12°F (1.18 °C), with most of the warming occurring in the past 40 years. Plant and animal life has significantly declined (as much as 50–68%) in the last 50 years. Human emerging infectious diseases (helminths, bacteria, viruses), many of which are zoonotic, have increased since tracking from 1940, comprising more than 44 million cases occurring in 219 countries. These oft-cited metrics are single-factor data points. The global alchemy is what’s important, requiring innovative, effective, and holistic science (1, 2).

Fortunate or not, I’ve seen these patterns emerge firsthand. My research focuses on global patterns of species extinction, zoonotic correlates of human emerging diseases, and economic investments in conservation action. I have served as a dean in a school of ecology, a member of the Council on Education of the American Veterinary Medical Association, and on the Board of Scientific Counselors of the Centers for Disease Control and Prevention. From this work, I now see a growing, perilous skew emphasizing the animal–human side of the human–animal–environment triad (3). For example, distribution of publications in relevant fields of study reveals relatively low integration (Fig. 1).

The interdisciplinary approach most likely to improve coordination among the requisite subfields is “One Health.” [Another approach, “Planetary Health,” is complementary, and the points here are equally pertinent (4)]. Coined in the early to mid-2000s, One Health is defined as an integrative approach from multiple disciplines working locally, nationally, and globally to attain optimal health for people, animals, and the environment (3, 5). Prominent papers and lead editorials (including those published by PNAS, the American Medical Association, and the American Veterinary Medical Association), dozens of university programs and institutes (mainly in veterinary colleges), governmental and nongovernmental organization (NGO) initiatives, a specialized task force of the United Nations, and many other topic-centric views all enthusiastically call for One Health (6). The approach is prescient. Most proponents advocate ratcheting up new methods and pedagogies, establishing basic scientific patterns and principles, and forging research programs that, quite crucially, will involve a rebalance and refocus of animal, human, and ecological practitioners.

Some of the disparity across animal, human, and environmental fields may simply relate to words. Einstein said, “The environment is everything that isn’t me.” People have a gut feeling of the environment, such that it is so universal, there’s only a vague connection with human health—air, land, and water are omnipresent; they’re a given, the background Muzak of life [note: the same presumption applies to the use of “ecology,” defined as the interrelationships of organisms with each other and with their environment (7)]. Contrast typical medical terms (contralateral, endoscopic, hypothyroid, scleroderma, contusion) with those in the ecological/environmental sciences (abundance, distribution, temperature, organisms, climate, ecosystem). Everyone supposedly knows and uses ecological terms; therefore, we’re all purported experts in the field and assume we know how ecology relates to One Health (8).

I propose four changes to help integrate ecology into animal and human medicine.

First, academic and governmental institutions need to hire faculty in human, veterinary, and public health units who are trained in ecological sciences; they also need to help retrain the current 10 million to 15 million medical practitioners worldwide to recognize ecological patterns associated with medical problems. One immediate example would be to focus on human and animal disease patterns, particularly in human disease hotspots and in areas of extreme heat and high densities of wildlife and livestock that contribute to disease spillover. Presently, disciplines that encompass studies of spillover are not focused on this complex, growing problem (ref. 9; see Fig. 2).

Colleges and programs of public health have broad conceptual scope of interdisciplinary scientific approaches, well-connected to One Health disciplines, and should be increasingly involved in community and societal engagement (14). Further, all physicians and veterinarians are required by state licensure to take Continued Education (CE), ranging from 25 hours per year to 200 hours per four years for physicians (15) and from 20 hours per year to 60 hours per three years for veterinarians (16). According to the American Medical Association definition of appropriate CE credit, ecological information will certainly provide “educational activities which serve to maintain, develop, or increase the knowledge, skills, and professional performance and relationships that a physician uses to provide services for patients, the public, or the profession” (17). CE courses are a direct opportunity to explicitly include ecology in medical training.

Secondly, institutions must develop rigorous core curricula with new ecological approaches to problems such as intraspecies and interspecies transmission of infectious diseases among animal and human populations; climatic (heat stress) effects on pathogen persistence and respiratory emergencies; and the impact of air pollution on such conditions as asthma, allergies, and cardiovascular disorders, to name a few. Specific ecological content (e.g., habitat selection, geographic range dynamics, physiological/thermal ecology associated with climate change, population biology and genetics, ecosystems and disease regulation) would serve as essential references to increase understanding of environmental effects (7). First- and/or second-year medical and veterinary curricula should expose students to these ecological topics, while at the same time covering core anatomical and physiological standards of general medicine. Affiliated, adjunct faculty from ecology and environmental science units would contribute, leading to joint interdisciplinary full-time equivalent appointments. Consistent language across subfields will be critical for successfully adopting shared, clear discourse for teaching One Health competencies: for example, how to measure and predict transmission rates of infectious diseases across animal, human, and environmental spectra. Basic ecological principles should be core prerequisites for human and veterinary medical and public health curricula (18). For instance, the NIH is sponsoring programs in medical schools to adopt environmental curricula to include a diverse range of topics such as wildfire smoke exposure on respiratory disease and impacts of climate and temperature changes on pregnancy (19).

It would likewise be beneficial to broaden the inherent definition and range of One Health to include plants. Plants have long had impact on the healthcare and pharmaceutical sectors, including diverse applications for infectious diseases, sedatives, cancer, and pain treatments (20). Such applications continue to increase significantly in the global herbal medicine market, which is valued at $233.08 billion in 2024 (21). Geographic overlap of plant species with the majority of terrestrial vertebrates will aid in this extension (22).

Overall, the goal is to provide instruction focused on the principles of ecological sciences in order to build a better understanding of the interrelationships of animals and humans in the environment. This will both improve knowledge to healthcare professionals and to the receiving public.

Thirdly, One Health practitioners should develop new approaches to unify scientific research. This will integrate required knowledge and understanding of the Earth, as well as the animal–human connections within it. Despite the COVID-19 pandemic grabbing our attention and making us increasingly apprehensive of other global devastations, such as heat-related deaths, overpopulation effects on natural resources, and irreversible losses of species biodiversity, we do not have answers to basic questions: What are pathways and probabilities of some interactions (e.g., infectious disease transmission) compared to others (e.g., heat- or flooding-related illnesses) within the animal–human–environment triad? Are there core differences between two-way (animal–human) and three-way (animal–human–environmental) interconnections, perhaps involving different mechanisms and temporal periods of change? Are some directional pathways (e.g., from animal to environmental to human) more common than others (e.g., human to environmental to animal)? How do we develop predictive measures of when interactions will occur? And, ultimately, what are the statistical probabilities of each connection occurring under different circumstances, analogous to statistical chances of diagnosing and curing cancer or diabetes?

Research funding agencies must invest in systems that identify and track large-scale animal–human–environmental changes. They must also look to expand applications of AI and machine learning to predict future health crises, as is customary in disease ecology (23). Broadly, research and educational training should be directed more to “why” questions—often adopting the longer view of identifying patterns of disease through ecological observation and metrics, in contrast to medical and public health approaches that focus on what and how to fix in the here and now (24). Recent developments of implementation science (defined as the emerging science of devising practical, real-world solutions to complex problems such as climate change) will accelerate and utilize research for policy and practice to improve One Health outcomes (25).

The fourth and final recommendation is that in order to advocate for One Health, researchers, physicians, and veterinarians must communicate clearly; work on a uniform language amongst all healthcare practitioners to prioritize sustainability, recycling, and responsible disposal of pharmaceuticals and waste; conserve clean air and water; and generally translate everyday behaviors to serve as One Health reminders. When’s the last time you visited a veterinary clinic or hospital where signs were posted about using or promoting sustainable medical materials, recycled and carbon-neutral products, and plastic-free packaging? Such supplies aren’t always possible, but reminders in all healthcare settings are. Business models and economic opportunities for “circular economic medical supplies” are on the rise (26), while sustainability of medical supplies and consumables are increasingly advocated, intending to reduce the (at least) 4.4% global net greenhouse gas emissions and toxic air pollutants from healthcare (27).

Currently, One Health is dominated by medical problems (3, 5, 8). It shouldn’t be. Global environmental catastrophes are on the rise—everything from infrastructure failures (building collapses) to wildfire burns wiping out entire communities to extreme weather events. These are severe problems outside the bailiwick of traditional medicine, but clearly within animal–human–environmental domains—for example, consideration of effects from climate change on learning rates, cognition, travel/movement patterns, food availability, and agricultural practices. We must shift the narrative of cultural differences amongst animal–human–ecological disciplines, establish global surveillance and database systems across disciplines, and develop better predictive models.

It’s true, of course, that the overarching, unifying word is “Health,” broadly defined by the World Health Organization as follows: “Clean air, stable climate, adequate water, sanitation and hygiene, safe use of chemicals, protection from radiation, healthy and safe workplaces, sound agricultural practices, health-supportive cities and built environments, and a preserved nature are all prerequisites for good health” (https://www.who.int/health-topics/environmental-health#tab=tab_1). As such, public health has an essential role to segue health, prevention of disease, and empowerment of individuals to manage illness and disabilities. In playing this role, public health unites disciplines, backgrounds, and divergent perspectives with environmental concerns now of paramount concern (28) within a One Health framework.

Fields of medicine cannot and should not effect these changes on their own. One Health requires and must involve all sides of the triad. Some of these proposed changes will succeed quickly when there are win–win–win solutions for each discipline to benefit, learn, and improve from reciprocity of other disciplines.

It’s impossible to separate human health from health of the natural world. Ecology is the unifying science that integrates knowledge and understanding of the Earth, as well as the animal–human connections within it. The scientific potential of a One Health approach is unlimited, exciting, and necessary for the health of life on our planet.

I thank Jonathan Davies and the Climate-Biodiversity-Disease Group for helpful discussion, the Council on Education of the American Veterinary Medical Association for encouraging One Health approaches, and Lauren Buckley for permission to use the maps.