What if our way of life causes other epidemics?


Zoonoses, these diseases that are transmitted from animals to humans, are on the rise. Science and the future re-examines the role of human activities in their emergence and spread.

According to’WHO (World Health Organization), “zoonoses (Greek zoon, “animals” and nose, “disease”), are a group of infectious diseases that are naturally transmitted from animals to humans. The greatest risk of transmission is at the interface between humans and animals through direct or indirect exposure to the animal, its products (eg meat, milk, eggs, etc.) and / or the environment.“. Lzoonoses, also called anthropozoonoses, can be viral (rabies, encephalitis), bacterial (salmonellosis, pasteurellosis, brucellosis), parasitic (toxoplasmosis, scabies) and mycotic – associated with fungi, editor’s note – (ringworm) “. Severity can range from a simple local reaction to a fatal disease.

OneHealth: when human health depends on animal health and the environment

In the reportInserm on zoonoses, Bernadette Murgue, director of research in the department for new viruses in Marseille, explains that “several agents of animal origin could cause epidemics with important consequences like Covid-19, or even more“These diseases are considered a major public health problem. Gilles Salvat, scientific director for animal health and welfare at ANSES, says that.”60% of current infectious diseases in humans are zoonoses. ” Adds: “We cannot treat human health without caring for animal health and vice versa“In the early 2000s, that awareness enabled the emergence of the movement. OneHealth (one health, in French), promoting the interdependence between human health, animal health and the ecosystem in which they coexist.

Diagram of the interdependence of human, animal and environmental health (OneHealth). Click here to see a larger image. © Inrae / computer graphics design: Michaël Lebourlout / July 2020

Environmental crisis responsible for animal diseases

The emergence and spread of zoonoses are major problems. They are strongly conditioned by modern human activities (associated with environmental degradation). Here are the most important activities.

  • Deforestation, by destroying or humiliating the habitat of a good number of animals, it creates the closeness of the latter with Man. This increases the risk of disease transmission. Virus Ebola in West Africa it is a glaring example. Wild primates – with their genetics close to human – have served as secondary hosts in the transmission of this virus, according to FRB (basis for biodiversity research).
  • Intensification of agriculture notrequires space, therefore it is established in new areas to the detriment of the land on which the flora and fauna initially lived. For example, 40% of the world’s arable land is taken up by food crops for livestock. This anthropogenic pressure on ecosystems has brought people into contact with new geographical areas and the wild species found there, the FRB expresses. It can lead to viral transmission from animals to humans, as would be the case with the Nipah virus (which can cause acute respiratory syndrome or even lead to death), which according to the WHO first appeared in Malaysia in 1998.
  • Globalization, through animal and food trafficking, thanks to international trade, have enabled global zoonotic epidemics. The increase in travel, for example, has allowed the circulation of infected people and mosquitoes, which can be carriers of diseases such as dengue, chikungunya or Zika. Fact, “some diseases on the WHO list have already spread in recent years. Like Zika, which has long remained confined to Asia and Africa and appeared in Latin America in 2015“, concludes the Inserm report on zoonoses.
  • Climatic and meteorological disturbances : speaking in Inserm file on zoonoses, Yannick Simonin, a virology researcher at the University of Montpellier, believes that “due to global warming and other factors mentioned above, the risk of developing these infections in our latitudes is not equal to zero. In this same report, Claire Lajaunie, a Marseille environmental law researcher, explains this “Global warming associated with greenhouse gas emissions could alter the area of ​​presence of wild species and vector insects, such as mosquitoesEarlier, various mosquitoes were closed in certain parts of the world. As temperatures rise, they are now able to colonize other warmer parts of the world than they have in the past. Another result of global warming is the melting of ice, which eternal frost, which would release viruses normally trapped in these ice sheets into the atmosphere.
  • Biodiversity loss : according toGOOSE (World Organization for Animal Health), “the great diversity of species allows pathogens to be diluted in a multitude of hosts or even stopped without ever reaching humansThis is known as the “dilution effect,” suggesting that natural biodiversity (and species diversity in particular) can reduce the risk of disease, including zoonoses. Lyme disease (transmitted by the mediator of an infected tick bite) is an example of a zoonosis, the spread of which would be affected by the loss of biodiversity.
  • Intensification of animal husbandry involves animal selection, which reduces species diversity (low genetic diversity) and thus increases the risk of spreading pathogens. In addition, these selections sometimes keep animals very susceptible to certain zoonotic diseases. According to a study published in the journal National Medical Library in 2010, “in this case the number of domestic animals serving as host reservoirs increases, the strength of the infection increases as well as the risk of human infectionIn the article from CNRS Journal, evolutionary biology researcher François Renaud specifies that: “until Originally, H5N1 is an extremely virulent bird virus, but it is not very effective in the wild: it kills its host, the bird, very quickly, resulting in limited transmission to other hosts. Factory breeding created the conditions for its success, thanks to the exceptional concentration of birds and the promiscuity of the birds, favoring the transmission of the virus. The passage to humans, despite among the species, ended due to the concentration of poultry in one place and deteriorating sanitary conditions. It is a game of trial and error: in theory, the bird virus is not transmissible to humans, but by trying to pass …“If we also take into account the stressful conditions on these farms, which weaken the immune system of animals, it seems that there are all the conditions for the appearance, proliferation and mutation of zoonoses.
  • Industrialization and food processing : “Foodborne infections are among the most important zoonoses in the world. ” declaresEuropean Food Safety Authority (EFSA) in the 2017 Zoonoses Report. Observations that would be exacerbated by our modern industrial processes. Food industrialization and processing increase food contamination by pathogens such as Salmonella spp (in the origin of salmonellosis, editor’s note) and some strains of Escherichia coli (responsible for gastroenteritis and potential kidney problems that can be fatal, editor’s note) “, points out a study published in 2010 in the journal National Medical Library.

Read alsoCompost, prevention against foodborne illness?

  • Domestication of animals onit also increases the risk of zoonoses. Poorly dewormed, dogs can transmit parasitic diseases to their owners. This is the case with the intestinal worm so called no ascaris (nematode Toxocara canis),, according to a study published in the journal National Medical Library in 2013
  • Intensive urbanization,, in origin destruction of certain habitats, drives animals towards cities. This is the case with rats that serve as a reservoir for certain diseases, such as leptospirosis (can lead to kidney failure or even death), for example, which is then transmitted to humans, the FRB states.

When the intensification of human activities rhymes with global epidemics

Therefore, as the FRB points out, “the constantly growing global human population and the exponential need for resources, the geographical expansion of human activities and the associated pressures are accelerating (agriculture, urbanization, industrial activities). There is currently very little space without anthropogenic footprints. It is the result of both the mass extinction of wildlife populations and the increased contact of Man with fauna whose habitat has been reduced. As this unprecedented anthropogenic pressure on ecosystems, in the context of global environmental change, is constantly increasing, zoonotic diseases will continue to emerge in the future.. “

Intergovernmental platform IPBESin his latest report he warns of the beginning of future epidemics stating this “Pandemics will occur more often, spread faster, kill more people and affect the global economy with a more devastating impact than ever before.Therefore, scientists specializing in infectious diseases have set up a platform to prevent future zoonoses. SpillOver, enabling the identification of the virus with the highest zoonotic risk. However, that probably wouldn’t be enough. It would also include changing our daily habits and a systemic approach to the ecosystem (taking into account the interdependence of humans, animals and the environment) to limit the risks of pandemics of a global nature.



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