One world, one medicine, One Health: an integrated approach to the health of our ecosystem

The World Health Organization (WHO) defines health as “a state of complete physical, mental and social well-being, and not simply the absence of disease or infirmity”. This statement clearly refers to human health conditions, but if we dwell on the adjectives that define well-being we can broaden their meaning by identifying a close relationship with the environment that surrounds us: our fellow men, animals and the natural context that we share with them. The social environment can be defined as a network of human relations regulated by respect for fundamental human rights (housing, food, education, health protection, decent and justly paid work). The WHO declaration has the merit of statements of principle: their meaning can be extended while remaining always open to the novelties of the times.


In recent years, a new vision has emerged regarding the topic of global health which has taken the name of One Health. The health of people is intimately linked to that of animals and the environment. According to this perspective, the approach to public health must be interdisciplinary, that is, make use of professionals in the field of human (medical) and animal (veterinary) medicine who work together with biologists, agronomists, ecologists, sociologists and economists. By now the whole scientific community is in agreement and the pandemic underway is a confirmation of this need.


The origins of the One Health vision

For centuries we have witnessed the close relationship between humans, animals and the environment. The first is represented by the fundamental treatise “De bovilla peste”, published in 1715 by Giovanni Maria Lancisi (1654-1720). Physician and archiatrist to Pope Clement XI, Lancisi is known for his important contribution to veterinary medicine during the rinderpest epidemic that struck Europe in the eighteenth century. In "De bovilla peste" Lancisi reports the main clinical characteristics of the 1711 rinderpest and discusses the control measures. Among these, one of the most important was the introduction of stumping out - the killing of infected animals - for which special practical recommendations are given: from how to conduct it, up to indications about the burial and the prohibition to move infected animals, as well as the description of the hygiene measures and policies appropriate to manage it. It also highlights the relationships between the livestock epidemic, famine and poverty in the human population, suggesting the necessary policy measures to be taken to address this social scourge.


Another example of the One Health approach is provided by the discovery of the smallpox vaccine by British physician Edward Jenner in the late XNUMXth century. The doctor had observed that cow milkers did not contract the disease and guessed that their immunity was due to contact with the cowpox virus (cowpoxvirus), belonging to the same family as that of human smallpox (smallpoxvirus). This observation allowed the formulation of a smallpox vaccine from smallpox pustules in cows. As a result, the disease has been eradicated around the world.


From zoonoses to the One Health concept

When we talk about One Health it is impossible not to refer to "zoonoses". This term was coined by Rudolph Virchow at the end of the XNUMXth century to indicate any infectious or parasitic disease that can be transmitted from animals to humans either directly (in contact with skin, hair, eggs, blood and secretions) or indirectly (through other vector organisms or ingestion of infected food).


In the same years an important contribution to zoonoses was made by William Osler, Canadian doctor considered the father of modern medicine and founder of the first medical clinic worthy of the name in the English-speaking world (Johns Hopkins Hospital in Baltimore), where, ahead of his time, he taught his students the value of empathy with the patient. This "master" was in fact the author of a fundamental treatise on internal medicine updated to the revolutionary discoveries of modern bacteriology and was among the first to support the importance of veterinary medicine as an indispensable discipline of public health, underlining the need for a broader vision for the study and health protection.


Today it is estimated that in the last thirty years about 70% of emerging human infectious diseases are zoonoses, or vector-borne diseases. The term emerging indicates the increased risk of animal-human transmission due to ongoing climate change.


The examples of zoonoses that endanger human health are numerous: yellow fever, brucellosis, rickettsiosis; then there is a significant number of parasites such as amoebiasis, schistosomiasis, trypanosomiasis, teniasis, toxoplasmosis, leishmaniasis, fascioliasis, trichinellosis (to mention only the most widespread) which maintain animal reservoirs and are increasingly capable of affecting humans. Among the most historically known zoonoses we remember the bubonic plague, salmonellosis, malaria, rabies. It is impossible not to mention the H5N1 avian flu, which first spread among poultry and later to humans, and the influenza pandemic caused by the H1N1 strain which, starting from a pig farm in Mexico, spread to the United States. Europe, Asia and Africa.


At the same time, the warming of the climate has facilitated the spread of some vectors and therefore of the diseases they transmit in areas where they were not originally present. The most studied case is that of the mosquitoes of the genus Aedes which transmit diseases once present only in tropical and subtropical areas but which are now widespread all over the world except the Poles. The best known is the Aedes albopictus (tiger mosquito), now present also in Italy and in the USA, which caused the emergence of West Nile and Chikungunya fever. We also remember the increase in tick-borne rickettsiosis in Europe.


The latest example in chronological order is the COVID-19 pandemic that we are now fighting. It is known that the virus originally infected bats and that (in ways not yet fully understood) it passed on to pangolin, civet or other wild animals sold in Asian market food stalls. Often these animals are kept alive (due to lack of the cold chain) and slaughtered at the time of sale: the inevitable contact of human hands with the blood, urine and feces of these animals is the factor responsible for the propagation of the virus that with the passage of time has made the "leap of species" animal-man.


From theory to action: One Health conferences and projects

The final recognition by the world scientific community of the One Health project came in 2004 with the presentation of the list of twelve principles, “The Manhattan Principles On One World, One Health” (Wildlife Conservatory Society, 29 September 2004, Rockefeller University). The close link between human health, animal health and ecosystem health was affirmed and the rules of interdisciplinary behavior were defined. Legislative guidelines were also suggested to make this approach operational: surveillance of the areas of close animal-human interface, potentially causing epidemics and pandemics, was recommended.


Since then, the implementation of various One Health projects around the world has begun, monitored and discussed in periodic conferences (World One Health Conferences). The last one was held online at the end of October 2020. More than 1700 participants, divided into 40 round tables and numerous master classes, brought their contribution. An important scientific contribution was given by low-income countries, especially in sub-Saharan Africa, where there are numerous health projects, such as the one in support of nomadic shepherds of Northern Kenya (Marsabit), managed by the friends of the Medical Collaboration Committee. of Turin.


In these projects, local communities play a central role: traditional knowledge on human health and animal care is enhanced and integrated by cooperating experts in these sectors. An example is brucellosis (a disease of a certain spread among shepherds and their families), caused by a bacterium present in the secretions of mammals (goats, cows, camels, sheep) to defeat which the simple boiling of milk is sufficient. before consuming it. But this is not enough: the other measure is the sensitization of shepherds to have their animals vaccinated: this is the only way to break the chain of transmission of the disease.


The conclusion is that there is no dividing line between human, animal and environmental health. The ambitious One Health project affirms an idea supported by over two centuries of medical and empirical practice: the absolute need for a transversal collaboration that brings together and draws on different professional skills in order to promote a unique and shared health. To achieve this goal it is necessary to deepen the knowledge of the interaction with the environment, promoting at the same time its protection and monitoring the most sensitive situations, such as the areas of close animal-human interface, hotbed of potential epidemics or pandemics. Nonetheless, population dynamics must be considered, making epidemiology an effective tool for the surveillance and control of common problems. An overall view, which evaluates all those biological, chemical and physical, but also social and economic factors that regulate the interaction between man and the environment; an integrated approach for preventive medicine that today more than ever must be the prevailing goal in Healthcare.




Article by Dr. Antonio Melotto

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