• The bat would be the natural reservoir of the Covid-19 epidemic, analyzes a virologist.

  • She could have transmitted the virus directly, or through an intermediate host, possibly the pangolin.

  • However, this should not tarnish the image of the bat, which is no more a carrier of viruses transmissible to humans than other animal species.

  • Cases of virus transmission from bats to humans, in France, are moreover almost impossible.

Responsible, but not guilty… The bat is probably at the origin of the Covid-19 epidemic, confirms the virologist of the Research Institute for Development (IRD) Eric Leroy.

If we do indeed find a lot of coronaviruses in bats, all animal species have however been the cause of diseases and epidemics in humans in the same proportions, insists the scientist.

And in France, there is no risk of transmission of this virus, or another, from bats to humans.

Despite everything, the reputation of this small animal is likely to suffer in France, fear environmental associations.

Yannig Bernard, from the chiroptera group in Aquitaine, wishes to reassure the population on this subject.

The two specialists explain what you need to know about the bat,

What do we know to date about the role of the bat in the origin of the Covid-19 epidemic?

“There has not yet been a specific study on the mechanisms and modalities that led to the appearance of the epidemic, nor on the transmission of the virus from its natural source to humans, explains Eric Leroy, research director, virologist, specialist in viral zoonoses at the Research Institute for Development (IRD).

The only elements currently available are elements of comparison: Sars-CoV-2 is very close to Sars-CoV, responsible for the Sars epidemic in the early 2000s. The horseshoe bat, a kind of bald -mice, being the animal reservoir of Sars-CoV, it is likely also the animal reservoir of Sars-CoV-2.

To support this hypothesis, sequences were found in these bats, very similar to the sequences detected in humans at the start of the Covid-19 epidemic,

in December.

To identify an animal reservoir of a disease, it is necessary to compare the viral sequences found in animals with those characterized in the first patients, because the virus evolves over time, and it will not be the same at the end of the pandemic, from what it was at the start.

All these elements show that bats are probably the natural reservoir of the current virus.

»

Did the bat transmit the virus directly to humans, or was there an intermediary?

In the case of Covid-19, “the bat is the reservoir host, that is to say that it permanently and asymptomatically harbors the virus”, tells us the virologist.

“Several scenarios are envisaged, concerning transmission to humans.

The first is direct transmission, which is what happens, for example, when these animals are eaten by local populations – and this is the case in Asia – when handling the killed animal.

Another scenario reports indirect transmission, with the intervention of an intermediate host, which could be the pangolin - an animal also widely consumed in Asia - but not only.

And another track would be a mix of the two, that is to say a virus which would be a genetic recombination between a pangolin virus, and a bat virus,

and it is this mutant which could have infected the human being.

The range of possibilities is therefore still quite vast.

»

Why do bats have such a bad reputation?

"It's an animal that has always had bad press, admits Yannig Bernard, a volunteer with the Aquitaine chiroptera group, because it lives at night, because there have been more or less baroque superstitions that have persisted for a long time, such as the myth of Dracula, which did not help, and which has long been said to get caught in the hair… However, we have the impression that there has been a change in recent years.

The usefulness of the bat is more highlighted: it is an insectivore that plays an important role in the regulation of pests, such as the corn borer or the mosquito.

The pipistrelle can eat several thousand mosquitoes in one night, but the local mosquito I specify, because the bat is not the good predator of the tiger mosquito which is diurnal.

It is also a consumer of vine predators,

he eats grape worm.

We have a big demand from winegrowers who want to bring bats to their estates.

»

Are bats generally a preferred host for viruses?

“Not at all”, assures Eric Leroy.

A 2017 study did however show a massive and diverse presence of coronaviruses in bats.

“Each animal species has its own particular viruses, and there are indeed a lot of coronaviruses in bats, and only within the horseshoe bat genus, confirms the virologist.

But viruses, there are hundreds and hundreds of them.

Other animal species harbor other types of viruses, and not all viruses are transmissible to humans.

The virologist insists: “It must be understood that all the major epidemics that have swept over populations for millennia have always been diseases caused by pathogenic agents, mostly from animals.

Indeed, bats have a number of physiological characteristics,

biological and ecological, which explain a great viral diversity hosted in them, but all animal species have been the cause of diseases and epidemics in humans in the same proportions.

The idea that circulates, that bats would be privileged reservoirs for human diseases, is therefore false.

»

Are species of bats of the genus horseshoe bat found in France?

Horseshoe bat species are insectivores and live in caves.

"There are different species of horseshoe bat all over the world, including in France, even if some are specific to certain regions of the world", explains Eric Leroy.

The species suspected in the Covid-19 pandemic,

Rhinolophus affinis

, lives only in Asia.

“There are a total of 34 species of bats in France, 26 of which have been identified in the territory of the former Aquitaine, adds Yannig Bernard.

There are three large groups of species in our region: those which are linked to the built space, which live in roofs, cellars, under the tiles, there are arboreal species which live in the holes trees, and there are species linked to underground environments, caves or quarries.

Populations are still significant in Aquitaine, especially in the Bordeaux conurbation where there are many common pipistrelle.

And all species of bats are protected, so it is forbidden to destroy them. 

Is there a danger of transmission from bats to humans in our regions?

“No, assures the virologist, with us the man has never been contaminated by a bat.

Some coronaviruses are hosted by bats living in our regions, but our way of life excludes direct physical contact.

The risk of transmission of a virus from a bat to humans in France is obviously not zero, but it is infinitely low.

At least not directly.

"I have been studying bats for twenty years, and I have never heard of diseases transmitted to humans with this animal in our country", confirms Yannig Bernard.

Even if the risk is almost nil, concerns around bats are likely to increase, and the reputation of the bat should still suffer.

“It's a fear, of course, admits Yannig Bernard.

This comes up every time there is a problem with bats, this had already been the case during the first SARS epidemic.

For the moment, people who are a little worried are calling us, and we are reassuring them.

»

Is it possible to anticipate the transmission of the bat virus to humans?

“We are at the third coronavirus which passes in humans, now we know that it is a virus with high zoonotic potential, that is to say possessing a capacity to pass from animals to humans much more important than other viruses, explains Eric Leroy.

So research must focus mainly on this viral family there.

They must be characterized as completely as possible, to highlight warning signals that tell us when a virus has evolved, and when it is close to being able to be transmitted to humans.

Then, we can put in place strategies to prevent a possible event.

»

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