Varun Landge A single bat may host several species of viruses and still not fall sick. They are the natural reservoir for viruses including the Marburg, Ebola, Nipah Hendra and rabies viruses, which have caused outbreaks in Africa, Malaysia, Bangladesh and Australia. There are over 1,200 species of bats known so far. The present outbreaks of coronavirus spreading from China may eventually be traced back to bats, the Chinese horseshoe bat. But how bats remain healthy while harbouring several viruses inside them which are dangerous to humans and other mammals. It is probably because of the immune system that lets them stay healthy while hosting disease-causing viruses that kill other animals. An international research team has found that bats can harbour such harmful viruses because of their ability to limit inflammation. In humans, the inflammatory response helps in fighting infection but also contribute to the damage caused by infectious diseases. Whereas, bats do not react to infection with such an inflammatory response, leading bats to skip pathological damage that is often seen with humans. The inflammation sensor- NLRP3 in bats hardly reacts in bats when compared to humans and mice. These sensors are usually triggered in fighting off stress and infection — body’s response when a pathogen invades. The natural ability of bats to evade such an inflammatory response caused by stress and infection may play a key role in the mechanism underlying in such a viral reservoir. When researchers compared the responses of immune cells from bats to three different RNA viruses, they found that the inflammation mediated by NLRP3 was significantly decreased in bats compared to mice and humans. Researchers have identified unique variants of NLRP3 which are present only in bats. They also compared transcriptional priming, which is a key step in making NLRP3 proteins, with mice and humans and found to have reduced in bats.
It seems surprising when an unrecognized disease and its causative viruses are discovered that lead us to wonder how such a virus could have evaded detection and whether it is a “new” virus. Ironically, one of the important practices to predict the emergence of zoonotic diseases that have been unnoticed repeatedly is the natural history survey. However, information about the natural history of most viruses in bats is limited.