This is why bats can carry deadly disease with little effect on their health

By Angela Heathcote 6 April 2020
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Understanding a bat’s immune system and replicating it in humans may just prevent disease outbreaks in the future.

BATS ARE BEHIND some of the worst disease outbreaks in human history, including the Ebola outbreak that still has West Africa in its grips and the SARS outbreak of 2003, another type of coronavirus, preceding COVID-19. 

Similar to the circumstances behind the SARS outbreak, it’s believed that COVID-19 began in a Chinese wildlife market, where it may have transferred from a host bat to an intermediary, suspected to be a pangolin, then onto humans. 

That bats are capable of hosting such deadly diseases with little effect on their health is of great interest to scientists such as Michelle Baker, a comparative immunologist who has led the bat immunology team at the CSIRO since 2008.

Bats may be a maligned species, especially in times like these, but understanding their incredibly robust immune systems may just be the key to fighting diseases like COVID-19 in the future. 

Michelle’s sequencing of the Australian black flying-fox genome in 2016 provided a major breakthrough, paving the way for a better understanding of their immune systems and how they differ from that of humans.  

Michelle’s sequencing of the Australian black flying-fox genome provided a major breakthrough. (Image credit: CSIRO)

“Whenever our body encounters a foreign organism, like bacteria or a virus, a complicated set of immune responses are set in motion, one of which is the defence mechanism known as innate immunity,” Michelle explains.

“We focused on the innate immunity of bats, in particular the role of interferons, which comes from their role in interfering with viral infections. They’re integral for innate immune responses in mammals, which helped us understand what’s special about how bats respond to invading viruses.”

Humans don’t have interferons switched on all the time because they can become toxic. They’re switched on when you become infected and turn off immediately after an infection has been dealt with. This process, however, is markedly different in bats. 

“In some species of bats, the interferons are switched on all the time, which allows them to respond quickly, with no delay between infection and activation, allowing them to maintain a comfy host-pathogen relationship,” Michelle says.

(Image credit: Jesse Hawley/CSIRO)

Michelle’s research also suggests that a bat’s immune system may have something to do with the evolution of flight. 

“As you can imagine, flight is highly metabolically costly” causing damage to DNA and proteins. Michelle believes that bats have made changes in their DNA damage and repair pathways to cope with the demands associated with flight.

‘We discovered that these pathways intersect with a number of innate immune genes which have also undergone some changes…so we think there have been inadvertent changes to the innate immune systems as a consequence of the evolution of flight.”

How exactly their immune system copes with the toxicity of the interferons is the subject of Michelle’s current research projects, however she says it might have something to do with the genes the interferons trigger.

“If switching on interferons is the first step, then the Interferons switch on hundreds of ‘interferon stimulated genes’ prompting various antiviral responses.”

While this research was published in 2016, it’s even more relevant now, during the COVID-19 outbreak. The endgame is to understand how we might redirect the immune system of humans and other animals susceptible to disease so they can have a similar response to bats. 

“If we can develop treatments for humans that make us respond like a bat… it would be groundbreaking.”