Beyond : To what extent are livestock activities a cause of virus transmission?
Daniel Mark: An infectious agent is never released from thin air. Whether it was Ebola, HIV in the 20th century or measles a few centuries ago, viruses always come from animals. It may first come from direct contact with the host, for example AIDS with chimpanzees. There are contaminants that are formed by an intermediate host, through which the virus is adapted to humans, which is the case, for example, coronavirus (2003 SARS was thus adapted to Civet). Finally, you can get infected by the bite of a vector, which is a stinging insect like the zika virus transmitted by mosquitoes or yellow fever.
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Therefore, it is logical that some rattles – diseases transmitted between animals and humans – have reached us through farming, but this is far from ideal.
Can we determine the number of epidemics in recent history that come from intensive breeding?
DM: Today, fashionable discourse, which speaks a lot to younger generations, aims to question intensive reproduction. We want to believe that it is the cause of everything, including epidemics.
There are precedents, of course, but they are the exception. I basically see two. For example, the 2009 influenza A (H1N1) influenza pandemic was the result of more than ten years of viral assembling between viral strains of avian origin, pig strains, and a human strain. Formed into pigs. It is in the pig fields that it is able to find a form that suits us and it has spread to the population.
The second is the Nippa virus which killed about 100 people in Malaysia in 1998. It was also transferred from bats to humans through pig fields. In this case, pig fields were built on forested areas that encroached upon the bats’ natural environment.
So will changing our agricultural model have no effect on epidemic risk?
DM: In my opinion, intensive or widespread reproduction, which changes nothing. In both cases, it is the fact of exposure to animals that explain transmission, not their numbers or their reproductive status. We also have a contradiction with the avian flu pandemic right now. It mainly affects the southwest as they practice breeding ducks in the open air and the virus comes from the wild world. On the other hand, intensive poultry farms, which are numerous throughout Europe, are safer than this because they are limited.
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One of the interpretations is that we are seven billion human beings compared to two billion in the early 20th century. We have a very high population density and increase in the flow of goods and people allow infectious agents to spread on all continents in a few days, especially by air transport.
That being said, an epidemic is an extraordinary fact that is difficult to predict, like a volcano that erupts or earthquakes occur. If we believe written historical sources dating back to the twentieth century, we see that there are three to four influenza epidemics per century, and this, before the birth of our agricultural model.
I think we have to live with this risk and respond scientifically. We have already been successful in eradicating the virus, such as smallpox (it was in 1978). This is an extraordinary fact, made possible only by the willingness of all actors concerned and fully confident in science and vaccination.