One Health provides a framework for collaboration and innovation across disciplines in a collaborative and interdisciplinary approach that recognises the interconnectedness of human health, animal health and the health of the environment. One Health fosters integrated solutions to complex health issues that transcend traditional boundaries by breaking down silos between medical and veterinary sciences, public health, ecology and beyond. This approach is critical for promoting health equity, environmental sustainability and resilience in the face of emerging global health challenges.
One Health emphasises the need for partnerships among professionals in human medicine, veterinary medicine, environmental science and other related fields to address health issues holistically. At its core, One Health acknowledges that human health is closely linked to the health of animals and the environment they share.
Why is One Health so important?
Most infectious diseases in humans are of a zoonotic origin, many of which are currently shared with other species. Changes in ecosystems can alter disease transmission patterns and threaten biodiversity. Indeed, addressing these environmental challenges is crucial for safeguarding global health. This example of the emergence and transmission of zoonotic diseases facilitated by the potential for pathogens to jump between species highlights how essential the One Health approach is for safeguarding the health of humans, animals and the planet and for preventing and preparing for the next pandemic.
[One Health] promotes early detection and response to emerging infectious diseases, thus reducing the risk of pandemics while providing more effective management options for existing health threats
The One Health approach offers a more comprehensive understanding of health challenges by examining the complex interactions between humans, animals and the environment. It also promotes early detection and response to emerging infectious diseases, thus reducing the risk of pandemics while providing more effective management options for existing health threats, including antimicrobial resistance, which affects both human and animal populations.
The idea of One Health goes back decades – at least to the initial idea of One Medicine for humans and animals – but has become much more prevalent in recent years, with a growing, if still insufficient, appreciation of the important role of the environment. In the 2020s, the concept gained new prominence both due to the COVID-19 pandemic, especially with the case of SARS-CoV-2 spreading between humans and minks, and the extension of the Tripartite for One Health. This tripartite consisted of the World Organisation for Animal Health (WOAH), the World Health Organization (WHO) and the Food and Agricultural Organization (FAO) of the United Nations (UN), and became a quadripartite with the inclusion of the UN Environment Program (UNEP).
A case in point: avian influenza in 2024
There is no better reminder of the importance of a One Health approach in research, public health and veterinary practice than the current H5N1 highly pathogenic avian influenza (HPAI) situation. HPAI H5N1 has been devastating bird populations, and isolated spillovers to wild mammals, such as foxes and seals, have been reported from several parts of the globe, thought to be related to mammals feeding on the carcasses of infected birds.
Then, in March and April 2024, a series of H5N1 infections in cattle were identified in the United States, with a strain known as “Clade 2.3.4.4b”. By the end of April 2024, the virus had been detected in 33 dairy cattle herds across eight states. Three human infections have also been identified in people with a close working relationship with cattle. However, the genetic evidence is still unclear on the exact transmission pathway between cows and humans.
While the immediate risk to humans from this H5N1 outbreak is low, the virus’s spread among cows raises concerns about potential mutations and future transmission
Genomic surveillance data, although incomplete, suggests the virus may have begun infecting dairy cows as early as December 2023. The true scale of the outbreak remains uncertain to date due to limited testing among animals and humans and the current lack of asymptomatic testing, which leaves significant gaps in understanding the extent of infection. Additionally, the virus has been found in milk in the form of non-replicating virus fragments, which are incapable of infecting cells. Further investigation found that a potential transmission route between cows was via milking machines and through aerosolisation of the virus on milking machines when they are cleaned with high-pressure water hoses.
As the outbreak in the US is an unfolding event, new information becoming available regularly. Latest developments in the outbreak can be found here, including an weekly updated timeline.
While the immediate risk to humans from this H5N1 outbreak is low, the virus’s spread among cows raises concerns about potential mutations and future transmission both in light of further mammalian adaptation and also due to the closer contact between cattle and humans than between previously infected wildlife species. This is particularly concerning as there is also the potential for the virus to spread from cattle farms to piggeries, with pigs being a key species in the transmission and spillover of influenza viruses, including to humans. Once again, this transmission potential shows how close working relationships between veterinarians, human medical practitioners, public health and, indeed, food safety is crucial to our response to emerging infectious disease threats.
Vets: the thought (and deed) leaders for One Health
Veterinarians have been essential in the detection and tracing of the current H5N1 outbreak in cattle – an outbreak that by its very nature is also of high importance to those in the human public health field. For a long time, veterinary practitioners have been key players in the One Health arena but also have the potential to be the group most suited to understanding and adapting to One Health thinking. The scientific and clinical training of veterinarians and their inherent ability to think about both individuals and populations equip them methodologically. Meanwhile, the profession’s awareness of its unique role as health professionals for non-human species allows them to adopt a broader view.
Veterinary practitioners have been key players in the One Health arena but also have the potential to be the group most suited to understanding and adapting to One Health thinking
While this line of thought is all well and true in an abstract, scientific contemplation, we need One Health in practice for better preparedness for emerging health threats and management of all aspects of life where humans, animals and the environment intersect and interact. This goes well beyond the control of infectious diseases – both emerging and endemic – but also includes issues such as food and water security and how life on Earth is changing under conditions of climate change.
As an applied infectious diseases epidemiologist, I am particularly pleased to see One Health being introduced more seriously into field epidemiology training programmes. This year, FAO, WHO and WOAH jointly published the first edition of a Competencies for One Health Field Epidemiology Framework, which lays out the technical and functional domains for skills and competency development for field epidemiologists that not only passingly acknowledge One Health but put the concept cross-cuttingly at the core of the training. It is essential that such efforts, alongside further integrated surveillance, such as in the case of collaborative surveillance, continue even once public attention to the pandemic starts to wane over the coming years.
Final thoughts
Emerging zoonotic diseases will continue to pose pandemic risks in our future; to be truly prepared as a scientific community and as a society, we need the voice of veterinarians and interdisciplinary dialogue. One Health offers a useful lens to facilitate this dialogue.
Emerging zoonotic diseases will continue to pose pandemic risks in our future; to be truly prepared as a scientific community and as a society, we need the voice of veterinarians and interdisciplinary dialogue
Veterinarians are well placed to continue to advocate not only for pandemic preparedness but also for prevention by highlighting how the health of humans is inherently also dependent on the health of the animals that surround us.
