The exact origin of the new coronavirus, which has already infected nearly four million people worldwide, is not yet known with certainty. But most scientists agree that it is an animal virus. Bats, for example, are a natural reservoir for many coronaviruses. Captured and sold alive on a market in the Wuhan region, they could have directly infected patient zero in the epidemic.
The case of the coronavirus is not isolated. The MERS virus in the Middle East, Ebola, HIV, etc. There are many examples of epidemics from an animal that have ravaged human populations. A better knowledge of these infections could facilitate the prevention and the fight against these diseases. Overview of these « zoonoses » in four questions by CQFD, the educational format of « Echoes ».
. What is a zoonosis?
The definition is apparently simple: it is an infectious agent of animal origin which is transmitted to humans, and which can make them sick. In reality, the definition evolves over time, or according to the research fields, explains Antoine Gessain, virologist at the Pasteur Institute, to the « Echoes ». It includes viruses, such as the new coronavirus, but also infections of bacterial or parasitic origin.
Scientists estimate that about two-thirds of the emerging viruses are of animal origin. It is especially mammals, which are closer to humans, who are at risk of transmitting these infectious agents to it. And it is generally wild animals which are at the origin of these epidemics.
. Besides the coronavirus, what other examples of zoonoses?
The new coronavirus, which paralyzes much of the global economy, is only the latest in a long history. It is not even, for the moment, the most deadly virus. Certain diseases of zoonotic origin thus persist in several regions of the world, even if they are transmitted very little from human to human. This is the case, for example, of rabies, which has emerged in wild carnivores and is transmitted each year to millions of people around the world, most often by stray dogs.
Two other coronaviruses have marked recent history. The first version of SARS (which stands for « severe acute respiratory syndrome ») emerged in China in late 2002 and killed nearly 800 people. And the MERS virus, which appeared in 2012 in the Middle East, continues to spread slowly in the region. The first comes from a bat and undoubtedly contaminated the man via a civet, sold on the markets of live animals in China. The second is probably transmitted to humans by dromedary.
This is also the case with Ebola, a virus which appeared in the 1970s in Sudan and the Democratic Republic of the Congo, and which continues to wreak havoc in Central Africa. Its natural reservoir is the bat. Particularly deadly, it was probably transmitted to hunters, before spreading to local populations.
Finally, the HIV epidemic, which has killed tens of millions of people around the world, also has a zoonotic origin. It is « probably blood contact between a hunter and a monkey », followed by a diffusion within human populations, which caused this pandemic, notes Antoine Gessain.
. Are these epidemics more and more frequent?
This is « probably » the case, notes the specialist from the Institut Pasteur. « Knowledge of these epidemics and the dissemination of information are much better, which leads to observation bias, » he observes. « But humans also have more and more contact with wildlife, » which increases the chances of contamination. « The data show that the number of epidemics is increasing despite this bias. »
Deforestation, for example to produce palm oil, leads to a loss of the natural habitat of animals such as bats, which serve as reservoirs for many viruses. Hunting and the consumption of bushmeat are all opportunities to come into contact with contaminated animals. Finally, large gatherings of people such as refugee camps are ideal grounds for the spread of an epidemic.
4. How to avoid them?
It is particularly difficult to anticipate the emergence of a new epidemic. What to do to protect yourself? For Etienne Decroly, a CNRS researcher specializing in emerging viruses, the fight against new epidemics requires, above all, better long-term funding for scientific research. “Veterinary surveillance”, in particular, provides a better understanding of new diseases. The risk is that interest will drop as soon as an epidemic is brought under control, as was the case for the coronavirus after the reflux of MERS and SARS-Cov-1.
The current epidemic has nevertheless shown the responsiveness of the scientific community, which has made it possible to sequence the virus in record time, nuance Antoine Gessain. “Better knowledge of the infectious agent promotes control of the epidemic. Screening tests have made it possible to slow down its dissemination ”.
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