For a while now, we haven’t known why bats are able to inhabit some of the most lethal viruses known, including everything from Ebola to SARS. But, new research suggests that it all comes down to the fact that flying is such hard work.

The revelation came after Peng Zhou, from the Wuhan Institution of Virology in China and his colleagues studied the immune systems of bats and flightless mammals. In doing so, they focused on free-floating DNA within cells. This can be a result of a viral infection, as the viruses hijack the cells’ DNA replication apparatus to copy their own genetic material. In addition, this can also happen during strenuous exercise, which in turn creates chemicals called free radicals that build up in cells and damage the DNA, releasing fragments of it. 

Most mammals don’t carry out such strenuous exercise, so their DNA rarely leaks out into their cells. As a result, if their immune system detects any free DNA, it interprets it as an emerging viral threat and begins fighting back. The trigger for action is a sensor molecule called STING, which swamps the viral infection with anti-viral substances called interferons. 

However, when bats fly it is extremely strenuous on their bodies which means their DNA often leaks out. This could eventually lead to the bat’s immune system to mistakenly attack the animal’s own tissues. In order to avoid this, bats appear to have evolved milder reactions to viral infections, allowing the bats and the viruses to be able to tolerate each other. 

In the study, Zhou’s team mimicked infections in the white blood cells of mice and of Chinese rufous horseshoe bats. It is worth noting that this is the species that harboured the SARS virus, which killed almost 600 and infected 7,700 during the 2003 outbreak. The mouse cells produced at least 10 times more interferon. The findings of which can be found in the journal Cell Host & Microbe

They then went on to compare the gene for STING in 30 bat species and 10 flightless mammal species, including humans. In all the bats, STING had lost the amino acid serine at one site, but in all the other mammals STING had kept it. The presence or absence of serine at that site dictated how the cells responded to fake viral infections. Therefore, by losing the serine, bats tolerate viruses that other mammals would fight off. 

Zhou explained, “Wild bats carry viruses for a long time at a low level, less like control and more like coexistence. A milder response to viral infection is not always a bad thing.

“Because some of these viruses may potentially lead to new global pandemics, it’s essential we begin to learn how the bats remain well and unaffected.”

 

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