Ebola. TORSO. Rabies. MERS. Most likely even the new coronavirus, CORVID-19. There is one animal that innocently and unwittingly gives all these evil scourges to humanity. The bats.
Why? Bats could be the ultimate incubator, according to new research, thanks to an incredibly efficient and robust immune system that essentially trains viral strains to adapt and evolve, becoming as adaptable and infectious as possible.
This is an unfortunate side effect of what is otherwise an amazing survival mechanism. This is not a misfortune for bats – that is, of course, for other species – because when viruses manage to pass from bats to other species of animals, including humans, the immune responses of the recipients are not able to withstand these attuned, effective and highly transmissible disease-causing microorganisms.
“The bottom line is that bats are special when it comes to placing viruses,” says pathologist Mike Boots at the University of California, Berkeley.
“It's no coincidence that many epidemics come from bats.”
In a new study, Boots and colleagues investigated viral infection in bat cell lines, including cultures of the Egyptian fruit bat (Rousettus aegyptiacus) and the Australian black flying fox (Pteropus alecto).
Cells called Vero cells from monkey (African green monkey, Chlorocebus) were also used as controls.
This is due to the fact that one of the molecular mechanisms in the immune system of bats is the lightning-fast production of a signaling molecule called interferon-alpha, which is triggered in response to virus infection. When interferon proteins are secreted by virus-infected cells, neighboring cells enter a protective, antiviral state.
The African green monkey cell line does not offer these benefits. In experiments when cell cultures were exposed to viruses that mimic the Ebola and Marburg viruses, the monkey cells died quickly. In contrast, bat cells resisted the viral onslaught thanks to their rapid signaling by interferon.
The paradox, however, is that interferon ultimately benefits viruses, even if it interferes with their ability to kill cells. While the signaling system prevents cell death, the infection nevertheless remains, and the virus begins to adapt to a defensive mode, at least according to the scientists' computer simulation.
“This suggests that having a really powerful interferon system will help these viruses persist inside the host,” says biologist and study author, Kara Brook.
“When you have a higher immune response, you get cells that are protected from infection, so the virus can actually increase its replication rate without harming the host.” But when it is transmitted to humans, we do not have such an antiviral mechanism, and we can face many pathologies. '
It's important to note that humans do have interferon alpha, but bats seem to carry viruses much more easily than we do.
Even when bats are infected with pathogens that can kill humans, they do not show obvious symptoms of the disease, but instead carry viruses as a long-term infection.
More research is needed to understand why bats' interferon systems appear to be more reliable and faster than ours.
“Critically, we found that the bat cell lines showed signs of an enhanced interferon-mediated immune response … which allowed for a rapid rate of cell-to-cell transmission of the virus,” the authors explain in their study.
The takeaway, the team says, is that the viruses that evolved inside the bats would cause increased danger if they passed on to subsequent hosts, including humans.
Sometimes an intermediary is involved, such as pigs, camels or horses. Whichever animal is lucky enough to become a carrier, it is unlikely that it will be ready for the fate that awaits them.
However, knowing how and why this happens is vital to fighting viruses.
“It is very important to understand the path of infection in order to be able to predict the occurrence, spread and transmission,” says Brook.
The results are reported to eLife.
