ONE HEALTH

With globalisation and climate change, the One Health concept wants to find a comprehensive approach to health, which includes human health, animal health and the health of the planet itself. 


There is a theory that if a butterfly flaps its wings on one side of the world, it could end up causing an earthquake on the other. This theory, involving endless coincidences, could simultaneously show us a surprising level of connection.


On the other hand, it is a fact that in recent years we have normalized diseases such as Ebola, Zika, Covid or Monkey pox; and that we have been passive observers to the appearance of new infections that reach us from anywhere in the world in record time. 

A situation without precedents in history, but that we have accepted with resignation and composure. Could it be true that today we are living in a world that is much more connected than we might believe at first sight? Or does what happens in one part of the world have immediate consequences on the other part?

A zoonotic disease is the name we give to the diseases transmitted from animals to humans, either directly or indirectly, through vectors such as arthropods. Covid-19 was one of these zoonotic diseases with all its inherent repercussions, along with the morbidity and mortality it caused. It is estimated that over 75% of new infections will also be zoonotic diseases. Moreover, there are up to 1.7 million viruses that could leap to the human species over the next few years. The fact is that we do not know the name of the next virus that could appear, nor do we want to know it, but we do know that it is our responsibility as human beings to look after the planet on which we live. The protection and love of nature that come naturally to indigenous peoples are not only compulsory today, both as respect for the world that is our home and as a legacy to our descendants, but ra- ther they are imperative to be able to turn around the situation we are living in.

The world is, as we have seen, a unit in which we are closely connected; and in which people, animals and the ecosystem are very closely linked. Therefore, global health involves animal, environ- mental and human health.

The One Health concept is paving the way as a necessary world strategy to approach this problem as a whole and including the planet as a priority factor for global health. A concept that allows us to delve into globalisation, into the importance of sustainable development, animal trade or the possible zoonotic diseases to which we are still exposed.

At the beginning of the year 2000 the World Health Organisation (WHO) introduced this con- cept to tackle the risks of public health that had increased due to globalisation and climate change. However, over the past few years, in the aftermath of the pandemic, this approach has become a top priority for all international health organisations.

The situation must be approached from a comprehensive, unitary point of view, which allows us to get ahead of future threats and tackle this problem from a pre- vention perspective, and not as a response to a disease.

We live in a world that is designed with a perfect balance; however, we are continuously altering this balance, generating many threats against ourselves and against the rest of the planet. It is alarming to think that 75% of the land surface area has already been significantly transformed by humankind, for its benefit.


Deforestation and changes in land use, trade and international transport, agriculture or industrial livestock farming are the three main determinants for the risk of zoonotic diseases over the next few years. But, how do climate change, or the conser- vation of ecosystems, increase the risk of zoonotic diseases? Climate factors play an important role in the incidence of diseases transmitted by vectors such as mosquitoes or ticks. World temperatures have increased significantly in recent years, with an accelerating trend to global warming. Mathematical models suggest that this situation will also speed up the transmission of diseases caused by mosquitoes and it will extend their geographi- cal distribution.

Global warming also has an important effect on the cycle of the ‘El Niño’ weather phenomenon, linked to a greater risk of diseases transmitted by different mosquitoes, such as Dengue or Rift Valley Fever. And the fact is that in dry climates, torrential rainfall provides ideal conditions for mosquito reproduction. Added to this, every year over 4,000 million people travel from one part of the world to another, with the consequent risk of disease transmission beyond the borders; as well as the continuous transport of animals from their habitats to urban markets and greater contact with wild and domestic animals, all mean that we have the perfect cocktail to increase the transmission of diseases from animals to people and, subsequently between countries, both quickly and globally.

Observing population movements, the current situation of the planet and the use we make of animals, is it surprising that what happened in Wuhan reached us, or that if there are no vaccines in Africa, a new omicron strain of SARS -CoV2 appeared in South Africa and moved from there onto the rest of the world; or that if a child eats monkey meat in the Congo and develops monkey pox, this infection ends up reaching us?

35 years ago, the Dalai Lama advanced: “As the world grows smaller, we need each other more than in the past... Now, more than ever, life must be defined by a feeling of universal responsibility, not only from nation to nation and from human to human, but also between humans and other forms of life.” We must look after our planet and all the living beings that inhabit it.


Animal health

Loss of biodiversity
Today, one million species are in danger of extinction; that is to say, one of every eight species could disappear in the near future. The decrease in the biodiversity and the extinction of species, which act as virus hosts, break the contagion chain or the naturally existing firebreak, turning people into direct hosts for these viruses.

Changes in the climate
It is well known that changes in temperature affect the abundance and the lifespan of ticks. Climate changes also affect bird migration patterns, which play an essential role in the propagation of zoonotic diseases. This situation has meant that pathologies such as Lyme disease, transmitted by ticks, have increased in recent years due to global warming. It has also caused cases of Crimean-Congo haemorrhagic fever to appear in Spain over the past few years (Extremadura or Castilla y León), and by direct transmission from ticks in the rural areas where they live.

Intensive livestock farming
Intensive livestock farming also has its effects on deforestation, in the high consumption of water and on soil pollution, through faeces and ammonia from the animal feed.


Human health

Fewer birds
Scientists from the Research Group of Hunting Resources Management and Wildlife at the Institute of Research in Hunting Resources and the Universitat de Lleida have studied the effects of urban expansion on bird migration in Europe and particularly, the migration of the common quail. The results emphasise that quails have not only lost their habitat In urbanised Europe, but that they are seeing their migration hindered by the large amounts of urbanised land and light pollution, which result in the quails colliding with infrastructures. From a ‘One Health’ point of view, this has consequences, as these common birds eat mosquitoes. The absence of the birds encourages the propagation of these insects, which also bite the dead birds and can transmit diseases to humans. Therefore, if the birds collide with infrastructures during their migration, the probability of a bird being bitten by a mosquito and that this insect then transmits a disease to a human increases considerably.

More resistant bacteria
Many of the bacteria that contaminate food have become resistant to antimicrobial agents, which make it more difficult to treat diseases transmitted by food. The correct use of antimicrobial agents in the production of meat, seafood, eggs and milk, as well as fruit and vegetables, can reduce the risk of bacteria resistant to antimicrobial agents in food.

Essential foods
60% of all human infectious diseases have a zoonotic origin and around 75% are transmitted between species. The high impact diseases affect essential foods derived from livestock, which make up 33% of the protein and 17% of calories ingested in food.



The environment

Climate
The variations in weather conditions, such as temperature, rainfall patterns and humidity have caused a direct effect on the length of the lifecycle of the Anopheles mosquito that transmits malaria. As a result, we are experiencing an increase in transmission of malaria in regions where the disease previously did not exist.

Deforestation
The clearing of jungle areas creates an ideal habitat for the reproduction
of the Anopheles mosquito in the Amazon, where the lack of trees means that the water is not absorbed and puddles and stagnant pools are formed, which seem to be the main facilitators for their propagation. It has also been seen that the mosquitoes that transmit malaria bite humans 200 times more in the deforested areas than in untouched jungle.

Agriculture
The deforestation of the Indonesian jungles to provide space for farming has meant that fruit bats have had to find another habitat, transporting a mortal disease along with them, transmitted by the Nipah virus. The consequence of this was the documented appearance of this infection in Malaysian farmers and the subsequent recurrent outbreaks all over South Eastern Asia.



by Dr. Yolanda Meije, 
Head of the Internal Medicine Service and the Unit of Infectious Diseases at the "Hospital de Barcelona". With record time. a doctorate in Medicine and Surgery and a Master in Infectious Diseases. She was employed as a researcher at the Boston General Hospital (USA). She has also worked at the Hospital 12 de Octubre, the Hospital Ramón y Cajal and the Hospital Vall d’Hebron.