Let’s start with the punch line: the bats didn’t give us the latest coronavirus. Its notorious cousins SARS-1 or MERS, or even the Ebola virus, have not been transmitted from bats to humans. So what happened?
A distant relative of the current coronavirus, SARS-CoV-2, was isolated from a bat in China. Genetic analyzes that looked for the similarity between the virus in bats and SARS-CoV-2, and took into account the theoretical rate at which the virus mutates, estimated that the two viruses separated five to five years ago. 50 years. In other words, one possibility is that about five years ago, the bat coronavirus succeeded in infecting another different animal – we don’t know which one right now. In this next animal, the coronavirus lived and mutated during those five years, and one day infected a human for the first time. There are also other hypotheses.
Science does not yet know where the coronavirus was hiding in recent years, when it became dangerous to people, or when the first person was infected, and we do not know which animal infected this first human. The only thing that science knows for sure is that the isolated Chinese bat coronavirus cannot have infected humans and is not harmful to humans.
This fact was published two months ago, based on the genetic sequences of the bat and human viruses. This is also true for SARS, MERS and ebola – despite repeated efforts to locate these viruses in bats, all the researchers found were similar viruses, or evidence of a previous exposure which does not mean that they routinely carried the virus and certainly not that they transmitted it to humans, despite information published in the general press (including in the Haaretz edition in Hebrew, April 19 ).
Bat Out of Hell
Why do bats get such bad press because of viruses? In recent years there have been growing claims that bats are carriers of zoonotic viruses, which can infect humans. But there are serious scientists who disagree with this and argue that bats are no different from other mammals in the number of zoonotic viruses they carry, certainly if you consider the large number of species of the bat family. About a fifth of all mammals in the world are bats.
There are several slim features that make them “suspicious” when it comes to viruses. Their ability to fly, their presence in all parts of the world, their large colonies and the overcrowding in which they live; their long life; and their proximity to humans makes them all conspicuously adapted to the transmission of diseases.
The fact that they are mammals increases the chances that they are transmitters. This is why the search for new viruses in bats has become almost a fashion among researchers; and the deeper the search, the more likely it is that something will be found.
In addition, the accumulated results show that the bat’s immune system is unique in mammals and competent in the fight against viruses. This immune system allows bats to repel viruses, including deadly viruses, by means of a moderate inflammatory response that leads to immunity. As a result, many studies find antibodies in bats – proof that they have been exposed to viruses – without finding the virus itself.
Without the living virus itself, the bat cannot be a carrier and certainly cannot be a transmitter. This means that the important link in the chain of zoonotic transmission to humans is still missing.
Eating a bat when sick can cause infection, just like any other sick animal could, and is not recommended. As a general rule, to reduce the risks of zoonotic transmission of viruses from bats or any other animal, it is preferable to eat them rarely and in general to minimize encounters with them; to let them live in their natural environment and stop invading their habitats.
Interestingly, the incredible immune system of the bats has apparently developed to support its unusual lifestyle. Bats live longer than almost all other mammals. In 2006, a Brandt bat (Myotis brandtii), weighing just 7 grams and the size of your finger, was recovered after being tagged by scientists in Siberia 41 years ago! A mouse of similar size would not live more than two years. Such extreme longevity requires an optimal immune system.
The flight ability of bats, unique in mammals, also seems to have contributed to the development of its immune system. In our studies, we have found that little bats weighing no more than 30 grams can cover a distance of more than 250 kilometers overnight. The energy requirements and the acceleration of the metabolism in flight are accompanied by oxidative damage which requires an appropriate immune system. Some believe that this immune system is the reason why bats very rarely develop cancer.
In addition, a bat that leaves its cave in the evening increases its body temperature by a few degrees in a minute. This elevated body temperature, which reaches 40 degrees Celsius or higher, apparently helps kill unwanted viruses and bacteria.
It is important to emphasize that our love for bats did not blind us (bats are not blind either). There are zoonotic viruses that are transmitted by bats like Marburg, Hendra, Nipah and bat rabies, none of which is found in Israel. Bat viruses should be given the respect they deserve, but there is no reason to attribute bats to viruses that are not their own.
Professor Yovel and Dr Weinberg teach in the Department of Zoology in the Faculty of Life Sciences at Tel Aviv University.