What is One Health? Why it matters for humans, animals, and the environment

When we think of health, many of us will picture doctors, hospitals and human medicine. Some might also think of veterinary care. But now, more than ever, health isn’t just about humans or animals in isolation. The health of wildlife, ecosystems and the environment are all deeply connected, all impacting each other, including human health. This interconnected approach is known as One Health, and I'm going to explain exactly why it matters.

What is One Health?

One Health is an integrated, unifying approach that aims to sustainably balance and optimize the health of people, animals and ecosystems ~ World Health Organisation (WHO)

One Health isn’t a completely new concept. Similarities between diseases in animals and humans have been observed since the 1800s, but it’s only in recent years that the approach has gained wider recognition and importance. Today, it is a globally recognised framework, supported by international organisations and reflected in major global health and conservation initiatives.

Why Does One Health Exist?

One Health exists as a way to tackle global health threats. There are several major global challenges that cannot be understood by simply focusing on human, animal or environmental health alone in isolation .

Some of the key issues that the One Health approach is crucial for include:

• Antibiotic Resistance - this is one of the biggest and fastest-evolving global health concerns. While antibiotic use in humans and animals may seem separate, many of the bacteria involved can move between species... and so can the resistance. When a bacteria becomes resistant to an antibiotic, that resistant strain can also infect other species including, wildlife, livestock and humans. Overuse or misuse of antibiotics across sectors can accelerate the development of resistance, making infections harder to treat across both veterinary and public health.

  
  

• Zoonotic Diseases - Dr. Virchow was a German pathologist, who first developed the concept of zoonosis, referring to infectious diseases that can pass between humans and animals. These are diseases are often responsible for large scale epidemics or even pandemics such as the Ebola Virus and Coronavirus. 70-80% of (re)emerging infectious diseases are known to be of zoonotic origin (WHO).

  
  

  This is particularly important to be aware of when working in veterinary or animal care roles. For example, in my role as a marine mammal medic with the British Divers Marine Life Rescue, it’s something we have to consider when attending rescues, as even marine mammals can carry diseases that may be transmitted to humans.

  
  

• Environmental Health & Biodiversity - human activity is driving major changes in ecosystems around the world, including habitat loss, climate change, pollution and biodiversity decline. A healthy, well-balanced ecosystem can act like a natural buffer for preventing zoonotic infectious diseases spilling over from animals to humans. However, these changes can disrupt natural systems increasing the risk of disease emergence, impacting not only wildlife health but also indirectly human health. This demonstrates how conservation is not only important in tackling issues concerning wildlife but also human health.

Although many of these issues have existed for a long time, they are being accelerated by factors such as population growth, climate change, habitat degradation, migration, and intensive farming. To address them effectively, we cannot look at human, animal, or environmental health in isolation. Instead, a truly interdisciplinary approach is needed which is where the One Health approach comes into play.

COVID-19 Example of One Health

An example that I'm sure many of us remember all too well is the COVID-19 pandemic. COVID-19 is believed to have originated from an animal source. With all other strains of coronavirus having a zoonotic origin (Holmes et al., 2021), it is likely there was an animal origin however the exact source still isn't known showing just how hard it is to determine and explain the full route in which the virus emerged.

Understanding how diseases move between species

When talking about diseases (pathogens) that pass between animals and humans, it’s helpful to understand a few key terms.

A reservoir host is a species that naturally carries a disease without being severely affected by it. These hosts act as long-term carriers, allowing the pathogen to exist and spread over time.

In the case of COVID-19, bats are widely considered the most likely reservoir host. Their immune systems are able to tolerate viruses that would cause severe illness in other species, meaning they don’t become affected in the same way.

Sometimes, diseases don’t pass directly from the reservoir host to humans. Instead, they move through an intermediate host, another species that the disease passes through before infecting humans. In the case of COVID-19 this is where the spread of the virus isn't fully understood. Species such as pangolins from live wild animal markets have been suggested as potential carriers. , although this hasn't been 100% proven.

This highlights how closely human and animal health are connected. Once the virus spread to humans it was able to jump across borders easily influenced by global travel, population density and human interaction with the environment.

This is a clear example of why a One Health approach is so important. Understanding how diseases emerge and spread across species, and how environmental and human factors contribute, is essential in preventing and managing future outbreaks.

Why One Health Matters?

Monitoring animal and environmental health alongside human health makes it possible to detect risks earlier, often before they become widespread problems. By understanding how diseases and environmental changes move across species and ecosystems, we can respond more quickly and effectively.

A One Health approach also helps improve prevention, not just response. By recognising the links between wildlife, ecosystems, and human health, we can reduce the likelihood of outbreaks, protect biodiversity, and support more sustainable health systems overall. Ultimately, One Health shifts the focus from reacting to health crises to preventing them, by recognising that the health of people, animals, and the environment are all part of the same system.

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One Health highlights something that’s often overlooked. The health of people, animals and the environment are not separate but deeply connected. Many of the challenges we face today can only be solved by joining the dots between these areas.

By understanding these connections, we can move away from reacting to problems and towards preventing them. As these challenges continue to grow, approaches like One Health are becoming increasingly important in shaping how we respond, not just in science, but in how we understand and interact with the world around us.

Follow along for clear, accessible breakdowns of research in One Health, conservation, and wildlife health.