One Health has been defined as "the collaborative effort of multiple disciplines — working locally, nationally, and globally — to attain optimal health for people, animals and the environment".
One Health is a new phrase, but the concept extends back to ancient times. The recognition that environmental factors can impact human health can be traced as far back as to the Greek physician Hippocrates (c. 460 BCE – c. 370 BCE) in his text "On Airs, Waters, and Places". He promoted the concept that public health depended on a clean environment.
The Italian physician Giovanni Maria Lancisi (1654–1720) was a pioneering epidemiologist, physician, and veterinarian, with a fascination in the role the physical environment played in the spread of disease in humans and animals. Lancisi may have been the first to advocate the use of mosquito nets for prevention of malaria in humans but was also a pioneer in the control of rinderpest in cattle. The idea that human, animal and environmental healths are linked was further revived during the French Revolution by Drs Louis-René Villerme (1782–1863) and Alexandre Parent-Duchâtelet (fr) (1790–1835) who developed the specialty of public hygiene.
In the late 19th century, German physician and pathologist Rudolf Virchow (1821–1902) coined the term "zoonosis", and said "...between animal and human medicine there are no dividing lines – nor should there be". Canadian physician Sir William Osler (1849–1919) traveled to Germany to study with Virchow. He returned to Canada and held joint faculty appointments at the McGill University Medical School and the Montreal Veterinary College. Osler was active as a clinical pathologist and internist at the Montreal General Hospital, but was also active in the promotion of veterinary health, and helped investigate a swine typhoid outbreak near Quebec City in 1878; he subsequently co-authored a monograph on parasites in Montreal's pork supply with A. W. Clement, a veterinary student at Montreal Veterinary College.
In 1947, James H. Steele, DVM (Doctor of veterinary medicine), furthered the concept in the U.S. by establishing the field of veterinary public health at the CDC. The phrase "One Medicine" was developed and promoted by Calvin W. Schwabe (1927–2006), a veterinary epidemiologist and parasitologist in his textbook "Veterinary Medicine and Human Health".
In 1996, Gary M. Tabor VMD MSc, Alonso Aguirre DVM PhD, Mary Pearl PhD, David Sherman DVM, Mark Pokras DVM, Eric Chivian MD, Paul Epstein MD and Gretchen Kauffman DVM launched the Conservation Medicine: Ecological Health in Practice effort (Consortium for Conservation Medicine) with the Cummings School of Veterinary Medicine at Tufts University, Harvard Medical School’s Center for Health and the Global Environment and EcoHealth Alliance (formerly Wildlife Trust), with a novel institutional focus linking human, animal and ecological health. This was first ever multi-organizational, multi-disciplinary effort to advance One Health practice.
The more recent use of One Health may be traced to a story about Ebola hemorrhagic fever on April 7, 2003, when Rick Weiss of the Washington Post quoted William Karesh, DVM as saying, "Human or livestock or wildlife health can't be discussed in isolation anymore. There is just one health. And the solutions require everyone working together on all the different levels." The following year, Karesh and colleagues Robert Cook, VMD and Steve Osofsky, DVM launched a series of conferences around the world with the theme of One World - One Health (see section below).
Emerging infectious diseases
Many emerging health issues are linked to increasing contact between humans and animals, intensification and integration of food production, and the expansion of international travel. As the number of new infectious diseases emerged in the 20th century, scientists began to recognize the challenges societies face regarding these threats that largely come from animals. Of the 1,415 microbes that are known to infect humans, 61 percent come from animals. For example, rodents transmit plague and typhus to humans, and domestic livestock are the original source of crowd diseases such as measles, mumps, and pertussis. One important exception is Mycobacteria tuberculosis. Genetic evidence suggests that Mycobacteria tuberculosis originated in human populations and spread to animals. Chimpanzees were a reservoir host for the human immunodeficiency virus. Global trade of wildlife exacerbates the problem of disease emergence.
The 1999 West Nile virus outbreak in New York City highlighted the links between human and animal health. In this outbreak, wild crows began dying about a month or so before people began getting sick. The simultaneous outbreaks were not recognized as caused by the same entity until Dr. Tracey McNamara, an astute veterinarian at the Bronx Zoo, tied them together when her exotic birds began getting sick. After it was recognized that the outbreaks were caused by West Nile virus, a new entity in the Western Hemisphere, the CDC established the National Center for Zoonotic, Vector-Borne, and Enteric Diseases, now the National Center for Emerging and Zoonotic Infectious Diseases.
In 2004, the Wildlife Conservation Society (WCS) convened a group of health experts at Rockefeller University in New York and developed the phrase "One World - One Health" in order to promote the recognition of the impact of land use and wildlife health on human health. William B. Karesh, one of the leaders of the WCS effort, wrote articles in Foreign Affairs about the health links between humans, animals, and the environment.
The avian influenza (HPAI H5N1) epidemic that began in Hong Kong in 1997 forced the global community to recognize that animal health and human health are linked. The 1997 outbreak affected 18 people, killed 6, and provoked the culling of 1.5 million birds. The HPAI H5N1 virus resurfaced in isolated outbreaks between 1998–2003, but a widespread outbreak occurred in mid-2003 in South Korea. Delays in international reporting and weak response measures contributed to the spread of the virus across Southeast Asia. In recognition of the global threat that avian influenza (HPAI H5N1) and other emerging zoonotic diseases posed, the Food and Agriculture Organization (FAO), World Health Organization (WHO), and World Organization for Animal Health (OIE) developed a strategic framework, a tripartite agreement, to work more closely together to address the animal-human-ecosystem interface.
Animals suffer from many of the same chronic diseases such as heart disease, cancer, diabetes, asthma, and arthritis as humans. Sometimes a disease entity is recognized in animals long before it is recognized in humans. For example, fear-induced heart failure was described in wildlife about thirty years before it was recognized in humans. Comparative medicine is the study of disease processes across species and is based on the study of naturally occurring diseases of animals that also afflict humans. The concept of comparative medicine is very old. The ancient Greeks understood that dissecting and studying animals could yield important clues to understanding human diseases. From Galen to William Harvey, comparative anatomical and physiological studies have been responsible for significant advances in medicine; Frederick Banting and Charles Best discovered insulin through such work.
The musculoskeletal system is particularly well-suited to comparative medicine studies since acute and chronic disorders of bones and joints have the same counterparts in humans and animals. Information gained from one species can be directly translated to another, thereby advancing the diagnosis and treatment of musculoskeletal disorders. Since the early 1930s, comparative orthopaedic research has incorporated the One Health concept. Otto Stader, a small animal veterinarian, used a comparative medicine approach and developed the first form of external skeletal fixation, the Stader splint, as a way to stabilize fractures in dogs. During World War II, Navy surgeons improved the treatment of fractures in sailors by incorporating Stader's advances. During the 1940s and 50's, Jacques Jenny, a veterinary surgeon, performed one of the first intra-medullary pinning procedures in animals and significantly advanced fracture repair strategies in horses and humans. In 1966, Sten-Erik Olsson VMD, MD and John L. Marshall DVM, MD, both of whom had medical and veterinary medical degrees, founded the first laboratory dedicated to comparative orthopaedic research at the Hospital for Special Surgery in New York. In the 21st century, comparative orthopaedic laboratories are located throughout the world and use both a comparative and translational research approach in an effort to improve diagnostic capabilities, enhance preventive and therapeutic strategies, and advance the understanding of disease mechanisms. Advances in fracture fixation, total joint replacement, and cartilage repair are a few examples of how knowledge flows in both directions, to benefit both human and animal health.
Urbanization, globalization, climate shift, and terrorism have brought the need for a more diverse public health workforce to the forefront of public planning. Changes in land use, creation and operation of large terrestrial and marine food production units, and microbial and chemical pollution of land and water sources have created new threats to the health of both animals and humans. For example, deforestation for agriculture can lead to the emergence of zoonotic diseases. Medical doctors are turning to environmental health scientists and practitioners to help them track disease outbreaks to the source, prevent chronic disease caused by chemical exposure, and create healthier living environments. Veterinarians are also turning to environmental health scientists and practitioners to prevent and control outbreaks and public health emergencies. One Health is the perfect unifying concept to bring together human health care practitioners, veterinarians, and public and environmental health professionals. By strengthening epidemiologic and laboratory investigations that assess the role of environmental influences, this partnership can help to develop and apply sustainable and effective community health interventions.
The One Health Commission: in 2007, Dr. Roger Mahr, the President of the American Veterinary Medical Association (AVMA), met with Dr. Ronald Davis, the President of the American Medical Association, to discuss bringing the animal and human medical communities together. Dr. Davis suggested that the best way for the AMA to get involved in such an endeavor would be to pass a formal "One Health" resolution. In June 2007, the AMA unanimously adopted this resolution. The AVMA established a One Health Initiative Task Force and passed a One Health resolution analogous to the AMA's resolution in July 2008. The One Health Task Force eventually became the One Health Commission headed by Dr. Roger Mahr. It is headquartered at Iowa State University.
The One Health Initiative is separate from the One Health Commission. The One Health Initiative website has been serving as a global repository for all news and information pertaining to One Health. Organizations promoting this movement are listed on this website and include the American Medical Association, American Veterinary Medical Association, the American Society of Tropical Medicine and Hygiene, The American Association of Public Health Physicians, the Centers for Disease Control and Prevention (CDC), the United States Department of Agriculture (USDA), and the U.S. National Environmental Health Association (NEHA). Additionally, more than 700 prominent scientists, physicians and veterinarians worldwide have endorsed the initiative. Additional history about the One Health Initiative is available at Horizon International, a non-profit organization based at Yale University, working to find and advance solutions to inter-related concerns of global health, the environment, and poverty.
In the USA, the CDC has a One Health website with One Health resources. The 1st International One Health Congress met February 14–16, 2011 in Melbourne, Australia. The 2nd International One Health Congress met January 29-February 2, 2013 in Bangkok, Thailand.
The World Bank is investigating how to demonstrate the cost effectiveness of a One Health approach to global health. In June 2012, the World Bank published the economic benefits of One Health.
The importance of One Health is promoted by scientists in many countries and supported by prominent organizations including the World Health Organization, Food and Agriculture Organization, World Organization for Animal Health, The International Federation for Animal Health, Global Alliance for Rabies Control, New Zealand Centre for Conservation Medicine (NZCCM), Hubnet in Asia the One Health Global Network, the University of California One Health Center, Academic Hospital Utrecht and Utrecht Life Sciences  and the Infection Ecology and Epidemiology Network, Uppsala, Sweden.
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