How bats can have several dangerous viruses without getting sick……..



Bats are known as hosts for various numerous viruses including Ebola virus, Nipah virus and  corona viruses such as severe acute respiratory syndrome (SARS) AND Middle East respiratory syndrome (MERS) and the latest 2019 novel corona virus (COVID-19) that infected 38 LAKH (approx.) people and killed over 13 LAKH (approx.) all over the world.  Although these viruses also cause harm in humans, But they rarely cause any type of harm in bats.
A study carried out last year and published in the journal Nature Microbiology   revealed the mechanism responsible for bats to harbor numerous viruses without themselves getting affected and also live long. Compared with terrestrial mammals, bats have longer lifespan.

HOW BATS DIFFER FROM OTHERS………

The reason why bats can have these harmful viruses without getting affected is simply because bats can avoid excessive virus-induced inflammation, which often causes severe diseases in animals and people infected with viruses.
When pathogens infect humans and mice, the immune system gets activated and typical inflammatory response to fight the microbes is seen. While controlled inflammatory response to fight infection helps keep humans healthy, it can contribute to the damage caused by infectious diseases, and also age-related diseases when the inflammatory response becomes excessive.
In complete contrast, the researchers found that the inflammatory response is dampened in bats immaterial of the variety of viruses that are present and the viral load. The researchers from Duke-NUS Medical School, Singapore used three different viruses  -Melaka virus, MERS corona virus and influenza A virus – and tested the responses of immune cell and other cells (peripheral blood mononuclear cells and bone-marrow derived macrophages) of bats, mice and humans to these viruses. While inflammation was high in case of humans and mice, it was significantly reduced in bats immune cells.


 Disease tolerance .......

“This supports an enhanced innate immune tolerance rather than an enhanced antiviral defense in bats,” they write. “This may also contribute to our understanding of the role of the inflammation in disease tolerance in bats as reservoir hosts” they say. This is in complete contrast to what is seen in mice and humans for disease-causing zoonotic viruses.
The researchers found that significantly reduced inflammation in bats was because activation of an important protein-NLRP3-that recognizes both cellular stress and viral/bacterial infections was significantly dampened in bat immune cells.
Studying further, the researchers found that reduced activation of the NLRP3 protein was in turn due to impaired production of MRNA (transcript). Since MRNA production is impaired the NLRP3 protein production gets compromised leading to less amount of the protein being produced. But this was not the case with mice and humans- there was no impairment to MRNA production so the NLRP3 protein was unaffected.
FOUR VARIENTS OF NLRP3.........

The NLRP3 protein is found as four variants in bats. The researchers found that the function of all the four variants was dampened compared with human NLRP3. To test if their finding on NLRP3 hold true in evolutionally distant bats, the researchers studied two very distinct species of bats – Pteropus alecto, which is a large fruit bat known as the Black Flying Fox, and Myotics davadii, a tiny vesper bat from China.