One Health: How to Achieve Optimal Health for People, Animals and Our Planet

We need a One Health approach, that is to say, one that takes into account that animal and human health are interconnected and linked to ecosystems.

The “One Health” concept, introduced in early 2000, refers to a notion that has been understood for more than a century: human health an animal health are interdependent and linked to the ecosystems where they coexist.

More specifically, One Health is defined as “the collaborative efforts of multiple disciplines”—medical, veterinary and research professionals, etc.—“working locally, nationally and globally, to attain optimal health for people, animals and our environment”.

3 changes that explain why One Health matters

The concept has recently acquired new importance in light of the changing dynamics of interactions between people, animals, plants and our environment.

Three changes stand out in particular:

1. The human population is growing and expanding into new geographical areas

As a result of this trend, many people are now living in close contact with wild and domestic animals. Although these animals play a very important role in our lives, more human-animal contact means a greater likelihood that animal diseases—known as zoonoses—will be passed on to people. Nearly 300 diseases are known to affect both animals and humans. We have long understood that animal health is essential to maintaining public health. According to the World Organisation for Animal Health (OIE), 60% of known human infectious diseases originated in animals (domestic or wild), as did 75% of the pathogens that cause emerging infectious diseases in humans.

2. Our planet is undergoing climate and land-use change, leading to deforestation and more intensive livestock farming

These changes in environmental conditions and habitats can make it easier for diseases to jump from animals to people. Intensive livestock farming has been associated with negative impacts on the environment and global human security. According to the United Nations Food and Agriculture Organisation (FAO), livestock farming generates more greenhouse gases than the global transport sector. The effects of intensive livestock farming include deforestation, high water consumption, and soil contamination via faeces (which release antibiotics and other waste into the soil) as well as ammonia from animal feed. In addition, the overuse of antibiotics in animals and the emergence of zoonoses pose serious problems for human health. Deforestation has many negative effects on the environment. One of the biggest impacts is habitat loss, which affects millions of species. These species are forced to seek out new niches closer and closer to human settlements, bringing them into contact with people and increasing the risk of zoonoses.

3. Global movements of people, animals and food have increased dramatically

International travel has become far more common in recent decades, allowing diseases and vectors of transmission to rapidly spread across borders worldwide. In our increasingly interconnected and interdependent world, the outbreak of an infectious disease in one country can become a health emergency of great concern to the entire world (e.g. COVID-19).

More human-animal contact means a greater likelihood that animal diseases—known as zoonoses—will be passed on to people

In short, these changes have facilitated the transmission of diseases between animals and humans by providing new opportunities for contact between people, animals and the environment.

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The areas in which the One Health approach is especially needed are food safety, zoonosis control and the fight against antimicrobial resistance.

One Health, a comprehensive solution to antimicrobial resistance

On the antimicrobial resistance front, it is well known that most of the antimicrobial agents used in veterinary medicine and human health care belong to the same families and share similar mechanisms of action. This increases the risk of resistant bacteria moving between humans and animals via the food chain or other routes of transmission (faeces, direct contact, etc.). It is highly worrying that some of the antimicrobial agents most commonly used in animals— colistin, for example—are the same ones reserved for the most difficult cases in humans. Transferable resistance mechanisms have been detected in bacteria of human and animal origin found in many different countries across the globe.

It is highly worrying that some of the antimicrobial agents most commonly used in animals—colistin, for example—are the same ones reserved for the most difficult cases in humans

One of the practices that has driven the increase and spread of antimicrobial resistance since the mid-20^th century is the widespread use of antibiotics as “growth promoters” to stimulate weight gain. Antibiotics have also been used in animals to prevent disease. This has led to the selection of resistant bacteria in animals, which reach humans via the food chain.

Water: A key role in the One Health approach

Water, an essential resource for life, plays a key role in the One Health approach. With increasing droughts and industrialisation, protecting this vital resource has become more challenging. Despite efforts, pollution continues to affect water quality, threatening both ecosystems and human health.

Chemicals, organic matter, microplastics and other waste are released into rivers and oceans, causing water pollution that can affect agricultural fields, animals and ultimately humans. This pollution also contributes to the loss of biodiversity, affecting everything from micro-organisms to larger species such as fish.

wastewater treatment plants are considered "hotspots" for the development of resistance. In these plants, bacteria of human and animal origin coexist with environmental bacteria, facilitating the exchange of antibiotic resistance genes

Sewage treatment plants play a fundamental role in this context. These facilities receive water contaminated with a wide range of pollutants, both organic and inorganic. But there is a key question: Are current treatments really effective in removing all contaminants? From a microbiological perspective, treatment plants monitor bacteria such as Escherichia coli, coliforms, Enterococcus, Clostridium perfringens and, in some cases, Pseudomonas aeruginosa. However, a critical factor is overlooked: the presence of bacteria that are resistant to antimicrobial agents. For this reason, wastewater treatment plants are considered "hotspots" for the development of resistance. In these plants, bacteria of human and animal origin coexist with environmental bacteria, facilitating the exchange of antibiotic resistance genes.

It has been observed that even after treatment, water returned to rivers may still contain antibiotic-resistant bacteria that are not part of the monitored groups and have survived the purification process. This water, which may be used to irrigate crops or water animals, can introduce resistant bacteria into the food chain, directly affecting our health.

In view of this situation, it is essential to incorporate the detection of resistant bacteria and resistance genes into wastewater treatment systems. This is the only way to stop their spread, in line with the One Health approach, which recognises the interdependence of human, animal and environmental health.

In conclusion, we urgently need to promote this transdisciplinary approach to improve the health of people, animals and our environment.