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More than 60% of all human pathogens worldwide are zoonotic, meaning they originate in animals. Well-known examples include rabies, the plague, anthrax, leptospirosis, and some influenzas. Most emerging infectious diseases are also zoonotic, including, for example, Ebola, HIV, SARS, and West Nile virus. 

The development of antimicrobial resistance, another critical issue in global health, also relates to animals and the environment. Widespread antibiotic use to “promote livestock growth” is associated, for example, with the development of resistant forms of bacteria. Resistant germs might spread from animal to animal, animal to human, or human to animal through food or contact. Resistant microorganisms can also develop in the environment. They can, for example, develop and spread on crops that are sprayed with fungicide. 

Many diseases occur at the intersections between the environment, animals, and humans. As a result, health authorities alone cannot address them effectively. Instead, addressing them requires a cross-disciplinary approach.

How we define "One Health" 

With the above in mind, increasing attention is being paid to “One Health.” WHO defines One Health as: “an approach to designing and implementing programs, policies, legislation, and research in which multiple sectors communicate and work together to achieve better public health outcomes. 

CDC (The US Centers for Disease Control and Prevention)  defines One Health as: “a collaborative, multi-sectoral, and transdisciplinary approach — working at the local, regional, national, and global levels — with the goal of achieving optimal health outcomes recognizing the interconnection between people, animals, plants, and their shared environment.”

One Health in practice

In practice, a One Health approach requires that specialists in human health, animal health, and environmental health work together to address problems at what we call the “human-animal-environment interface.” This could include, for example, clinicians, epidemiologists, and public health practitioners; veterinarians and agriculture specialists; and ecologists. Some people might say that this work must be done in a “multi-disciplinary” or “cross-disciplinary manner.” However, highlighting the importance of a perspective that crosses disciplinary boundaries collaboratively, CDC refers to One Health as being carried out in “transdisciplinary” ways. One article defined this as an approach that “integrates the natural, social and health sciences in a humanities context, and transcends their traditional boundaries.”

There are many public and global health areas where people, animals, and the environment share threats and where a One Health approach is needed. The most fundamental will include zoonotic diseases, antimicrobial resistance, food safety, and food security, vector-borne diseases, and environmental contamination. 

How could a One Health approach be used? 

One example of using a One Health approach in a “real-life situation” concerns an outbreak of drug-resistant Salmonella Heidelberg in the US from 2015 to 2018. A One Health approach to investigating this outbreak led to the findings that people were infected from dairy calves and their environment. Another example has to do with rabies. WHO estimates that 29 million people get a post-exposure rabies vaccine in the world every year. Trying to reduce the burden of animal bites can only be done when specialists across various disciplines work together. Another example concerns zoo animals that have been infected with SARS-CoV-2, the virus that causes COVID-19. One instance of this was the infection of otters at the Georgia Aquarium in Atlanta, Georgia, in the US. A transdisciplinary team was needed to understand how the otters got infected and how it could be assured that the infected otters did not spread the disease to humans. 

It is also clear that concerns about the present pandemic and fears of other pandemic threats have highlighted the importance of the One Health approach to the global health community. In addition, climate change, population growth, urbanization, and migration pose growing threats at the environment-animal-human interface and further highlight the need for a One Health approach to a broad range of global health issues.

So, what do we need to know?

There will be some critical issues in global health, such as vaccination against childhood illnesses, in which a One Health approach may not be so important. However, as noted above, in many other domains, those who work in global health cannot understand or effectively carry out their work without taking a One Health approach. Given the global health threats of today and those that may arise in the future, I would suggest that students and practitioners of global health need to understand the One Health approach and consistently use it as another lens with which they view global health issues. Just as they apply an equity lens to all that they do, they also need to apply a One Health lens to the problems they seek to address.

The One Health Commission was founded in 2009 in Washington, DC, and “seeks to bring together the human, animal, and environmental sciences in a value-added information exchange that improves the well-being of animals, sustainability of the environment and the lives of people and the global society.” The Commission’s website contains an extensive chronological listing of resources on One Health. This is an excellent starting point both to educate ourselves and seek materials that we can use to help our students gain a One Health perspective.