Bats’ immune systems are so efficient that viruses that infect animals have no choice but to reproduce at full steam to try to survive, researchers at the University of California at Berkeley have found. .
This ferocious immune response keeps bats from getting sick, but it also prepares viruses to wreak havoc if they jump to a species – like humans – whose immune systems aren’t as good, they add. they in the scientific journal eLife. This could explain why health problems like severe acute respiratory syndrome, Middle East respiratory syndrome, Ebola, Marburg disease and now Covid-19 often seem to go through the bat before they get to human.
“For some time now, we have realized that the bat has a natural resistance to several viral infections,” explained Carl Gagnon, a specialist in animal viral diseases who teaches at the university’s faculty of veterinary medicine. from Montreal. It is (…) an animal species which can harbor several viruses without necessarily being infected with it. “
In the presence of an invader, the bats’ immune system almost instantly produces interferon alpha, a molecule that prevents all cells from preparing for battle before they are invaded by a virus.
In laboratory experiments, this early warning enabled certain bat cells to guard against infection with the terrifying Ebola virus. The perverse effect of this protection is that it allows the virus to persist in the body of the bat, and therefore to continue to reproduce, without killing it.
“In the study, they seem to say that the bat is like a superchampion to make interferon,” said Gagnon. If we compare between the different species, this may explain why it is able to fight viral infections more aggressively.
“But interferon is a molecule that all mammals have. Maybe that of the bat is synthesized faster, in larger quantities, but it can also be much more effective, so it sure has an impact on the antiviral response. “
Overgrown environment
American researchers have found that bats in their invaded environment are more stressed and begin to shed more viruses in their saliva and feces, increasing the risk of transmission to another species.
Mr. Gagnon and his colleague Jean-Pierre Vaillancourt _ the deputy director of the Institute of research in public health of the University of Montreal and him also professor at the faculty of veterinary medicine _ agree besides to say that the impact of greater proximity between humans and animals should not be underestimated.
“The emergence of infectious pathogens from wildlife is not a new phenomenon, but it is one that appears to be growing,” said Mr. Vaillancourt. But everything is growing: the world population is growing, the animal population is immense, we are ending up in territories where we did not go before, among other things with climate change. Either voluntarily or involuntarily, we are going to invade ecosystems that we left alone before. “
Mr. Vaillancourt also believes that it is “not surprising” that such hatches occur in China, since “in (Chinese) culture, among others they have a lot of live animal markets, so that plays a role important, large animal densities and spectacular human densities ”.
About 60% of the approximately 1,500 infectious diseases found in humans are zoonoses, said Vaillancourt,
namely diseases shared by animals and humans. In addition, he says, over the past few decades, about 75% of new emerging diseases affecting humans have been of animal origin.
“The fact that we have an emergence of cases which would come from the bat – we did not only have the coronavirus, we had outbreaks of other types of virus _ it is in fact the proximity that we have more and more with bats, directly or indirectly, added Mr. Gagnon. You have to look at the ecosystem as a whole. I don’t think the viruses were there before. It’s just that there is a greater risk of being in contact. “
The world population, in 2020, is not only aging due to advances in medicine, but also more fragile, more mobile and more in touch with nature, recalls Mr. Vaillancourt, which “created opportunities (…) for pathogens like that to express themselves. “
The current coronavirus crisis may therefore be only a glimpse of what lies ahead.
“H5N1 has never been expressed at a pandemic level because it (the virus) has not yet found a way to be easily transmitted between human beings, which is different from the coronavirus,” he warned. . If it had been necessary for this virus, which is still possible, to transform and become easy of transmission between human beings, well it can be spectacular. “
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