In popular culture, bats are routinely portrayed as vile creatures, the minions of evil forces, such as vampires.
True to form, bats have made headlines again as potentially deadly animals. Namely, they have stood out as the possible host of the new SARS-CoV-2 coronavirus, which jumped to humans in China late last year. The coronavirus causes Covid-19, a disease that has infected millions and killed hundreds of thousands of people around the world.
However, the bad reputation of these flying mammals, which have about 1,200 subspecies and account for about a fifth of all mammalian species on the planet, is not deserved. Bats perform vital ecological functions: they pollinate plants, help disperse seeds in forests, and control insect populations.
Bats, reservoirs of viruses
However, it cannot be denied that they are also possible virus reservoirs. In fact, after examining 36 species of bats from the western part of the Indian Ocean, a team of researchers recently discovered that many of them were hosts to unique strains of coronavirus.
The scientists took swab and blood samples from more than 1,000 bats of three dozen species on the islands of the region, as well as some coastal areas of Mozambique in Africa. According to the scientists, eight percent of the bats they sampled were found to have a coronavirus.
"We discovered that there is a deep evolutionary history between bats and coronaviruses," says Steve Goodman, a biologist at the Field Museum in Chicago who lives in Madagascar and is the author of a new study published in Scientific Reports.
An evolutionary history stretching back millions of years
"We found that, for the most part, each of the different genera of bat families for which coronavirus sequences were available had their own strains," Goodman explains.
"Furthermore, based on the evolutionary history of the different bat groups, it is clear that there is a profound coexistence between bats (at the genus and family level) and their associated coronaviruses."
The expert cites the case of fruit bats in the Pteropodidae family, which can be found on various continents and islands. They live in groups of trees and are hosts to strains of coronavirus that are different from those of other groups of bats that live in the same geographic areas.
“Developing a better understanding of how coronaviruses (in bats) evolved can help us build public health programs in the future,” Goodman emphasizes.
Simultaneously, another team of researchers from the University of Saskatchewan in Canada discovered how bats that carry the coronavirus that cause Middle East Respiratory Syndrome (MERS) can do so without getting sick.
"Bats do not get rid of the virus and yet they do not get sick," says microbiologist Vikram Misra, who worked on a new study, which was also published in Scientific Reports. "We wanted to understand why the MERS virus does not turn off the immune responses of bats as it does in humans."
The key is immunity
An insectivorous brown bat can remain infected with the MERS coronavirus for months because cells in the mammal's body and the virus have come to coexist, the researchers say. "Instead of killing bat cells as the virus does with human cells, the MERS coronavirus enters a long-term relationship with the host, maintained by the unique" super "immune system of the bat," says Misra.
In response to the presence of the MERS coronavirus, the cells of a host bat adapt by maintaining a natural antiviral response rather than producing inflammation-causing proteins that would make the animal sick. At the same time, the MERS virus adapts to bat host cells by rapidly mutating one of its own genes. The result of these mutual adaptations is that the virus remains dormant for long periods in bats unless balance is affected by disease or other stressors, Misra says.
"SARS-CoV-2 is believed to work in the same way," adds the researcher.
Needless to say, humans do not have a defense mechanism similar to the new coronaviruses, which means that pathogens that are relatively harmless in bats can easily make us sick and kill us.