Don’t Blame the Bat
The new coronavirus spreading across the globe and the SARS outbreak of 2003 have two things in common: Both are from the coronavirus family and both were likely passed from animals to humans in an animal market.
Since the SARS outbreak 18 years ago, a large number of severe acute respiratory syndrome-related coronaviruses (SARSRCOV) have been discovered in their natural reservoir host: bats. Full-length genome sequences were obtained from five patients at the early stage of the outbreak. They are almost identical to each other and share 79.5% sequence identity to SARS-COV. Furthermore, it was found that SARS-COV-2 is 96% identical at the whole-genome level to a bat coronavirus. The pairwise protein sequence analysis of seven conserved non-structural proteins show that this virus belongs to the species of SARSrelated coronavirus (SARSR-COV). The SARS-COV-2 virus was then isolated from the bronchoalveolar lavage fluid of a critically ill patient, which can be neutralised by sera from several patients. Importantly, it has been confirmed that this novel COV uses the same cell entry receptor, ACE2, as SARS-COV.
This has happened with other coronaviruses. In the case of SARS, a bat coronavirus jumped to civets, a member of the mongoose family, and was sold to people as food at markets. Plus, the bat population from which the SARS virus originated lived in a cave just over a kilometre from the nearest village.
The MERS (Middle East Respiratory Syndrome) outbreak, first detected in 2012, was caused by a coronavirus that jumped from bats to camels to people who most likely drank raw camel milk or ate undercooked meat. Likewise, the novel coronavirus is believed to have jumped from bats to snakes, and then to people.
In Southeast Asia, fruit bats were the original hosts of the deadly Nipah virus, which emerged in Malaysia in 1998 and then again in India in 2001. The bats passed it to farmed pigs, which gave it to people. Patients experienced headaches and vomiting, while many slipped into a coma and died. Fruit bats in Africa have played a major role in Ebola outbreaks since 1976. The worst Ebola outbreak in history, however, came from a population of longfingered bats. More than 11,000 people were killed from 2013 to 2016.
There are over 130 different kinds of viruses found in bats, creatures of community that gather in large, crowded
colonies together. Members of different bat species share caves and hollowed out trees in groups up to the millions, where viruses can pass easily between them through close contact with each other. There are also billions of bats and more than 1,300 different species living on every continent except Antarctica. They have long lifespans relative to their size, and can live for more than 30 years, giving them a long time for them to be persistently infected with the virus and shed it into the environment, whether through urine, faeces, or saliva. They can also fly across large geographical ranges, transporting diseases as they go, which makes them an ideal host.
With this, you might wonder: Why aren’t the bats themselves affected by the viruses? The answer has to do with the bat being the world’s only flying mammal.
During flight, a bat’s body temperature spikes to over 37.7 degrees Celcius, and its heart rate can surge to more than 1,000 beats per minute. For most land mammals, this could trigger death, but bats live it every day, suggesting a developed special immune system to deal with the stress of flying.
Bat’s bodies manufacture molecules that other mammals don’t have, which help repair cell damage. And their systems don’t overreact to infections, which keeps them from falling ill from the many viruses they carry. Thus, it’s not always the virus itself but the body’s response to the virus that can make us sick.
The problem occurs when the viruses jump to new species – and it’s human activity that makes that likely to happen.
In wildlife markets, like the one in Wuhan, animals that rarely mix in Nature come together, and so a bat in a cage could be stacked over a civet. And those animals are then mixed with humans, say by butchers handling animals without gloves.
While the animal in the middle is still a mystery (some reports point to pangolins, while some are sure it is via snakes), it’s easy to imagine how an infected animal could spread the virus to humans. The animal could sneeze or urinate, and when a human touches it and touches their face, they become as good as infected.
Cooking an infected animal likely inactivates the coronavirus through heat. However, the preparation of raw meat carries risk. While it isn’t clear exactly how the virus spreads from animals to people, when an infected animal is killed and then skinned, small pieces of tissue or droplets of blood could spread into the air and transmit the virus.
Researchers stress that bats aren’t just a possible source of viruses – they play a hugely important role in Earth’s ecosystem. Bats eat many insects, pollinate plants and disperse seeds for hundreds of plant species. And they’ve found a way to coexist with the viruses they carry, which means that even though bats may be the source of viruses that affect humans, they could also be the source of a potential remedy if we study their immune systems.