How do bats transmit so many viruses without getting sick?


  • Bats can carry many viruses, including rabies.
  • But according to an Israeli study, bats are not the cause of the Covid-19 pandemic. For Ebola, as for Covid, the responsibility of bats could not be proven, for lack of relevant scientific arguments.

During recent epidemics, bats have often been singled out. Indeed, it is, despite itself, the relay of many viruses which can then be transmitted to humans and thus become a zoonosis : an infectious disease passed from animals to humans. Nipah virus, Marburg virus, certain coronaviruses… many are the pathogens that choose it as their preferred host.

But while they are capable of causing sometimes severe symptoms when they infect other animal species such as humans, why do they remain silent in the bodies of bats? Why do they have the power to never get sick from these deadly viruses? This question, a French team of researchers from the CNRS, the University Claude Bernard Lyon 1 and the ENS Lyon tried to answer. The results of their study were published on November 24 in the journal Science Advances.

Certain genes of the bat allow it not to get sick

For this study, the researchers gathered a variety of data from different scientific disciplines: virology, molecular and cellular biology, eco-epidemiology and genetics. They analyzed the evolution of genes in several species of bats and observed, at the molecular level, how the organism of these flying mammals had adapted during epidemics. Result: this bat superpower is due to special genetics.

“The answer lies, among other things, in the number of copies of the PKR gene, which participates in the immune response against viruses, can we read in the Press release relating to the study. While the majority of mammals have only one copy of this gene, some bats have several. So many copies that allowed the animal to diversify its antiviral repertoire, and thus to deal with a diversity of viruses.” But why, among mammals, is it only bats that have this particularity? “This characteristic was made possible by duplications of the PKR gene, and the ‘positive natural selection’ of these, during the evolution of the animal”the statement said.

Bats also have a different immune system than ours.

Another study, published in the magazine Immunity on November 8, adds one more element to this explanation. Scientists at Duke-NUS Medical School investigated the immunity of bats, focusing on one species in particular: the lesser aeonyctera (Eonycteris spelaea) that lives in Southeast Asia.

In this research, the scientists studied the immune responses of these bats to the Melaka virus which uses them as a natural reservoir. This virus causes mild respiratory disease in humans. Through their analyses, they discovered that a type of white blood cells, called neutrophils, showed very high expression of a gene called IDO1. According to them, this gene could play an important role in limiting inflammation after infection.

“We also found marked antiviral genetic signatures in white blood cells, called monocytes and alveolar macrophages, which in a sense consume viral particles and then teach T cells how to recognize the virus. This observation is interesting because it shows that bats clearly activate an immune response following infection despite few outward symptoms or pathology”explains Dr. Feng Zhu, co-author of the study, in a communiqué.

Studying bats could help us fight viral infections

The team also identified an unusual diversity and abundance of T cells and “natural killer cells” – named for their ability to kill tumor cells and virus-infected cells – in this bat that are widely activated. to respond to infection.

“We hope that by understanding how bats’ immune responses protect them from infections, we can find clues that will help humans better fight off viral infections.”, says Dr. Akshamal Gamage, another author of the study. His Duke-NUS Medical School colleague, Wharton Chan, adds: “And knowing how to better fight viral infections can aid in the development of treatments that will help us look more like bats, get sick less and age better.”

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