Bats are amazing creatures. Not only is it the only mammal that can fly consistently, but it also has amazing immunity. Even if they are infected with viruses that are deadly to humans, such as Ebola, Marburg or rabies, they remain unharmed and rarely get sick. This mysterious phenomenon has also fascinated scientists.

Why do bats have this ability? What can we humans learn from them? Let's start with the bats themselves.

A large family in the shadows

Carrying a deadly virus

When we think of bats, we may easily think of "vampire" or the figure that walks through the night of Gotham City. But when asked what bats look like, we may often only have a vague impression of "rats with wings...... This is probably because we don't usually have the opportunity to observe bats up close - after all, bats can fly, and most of them are diurnal and nocturnal, which also gives us the illusion that bats are "niche creatures".

In fact, the bat family is quite large. So far, there are more than 6400 known bat species. There are only more than 0 species of mammals. Bats alone account for more than one-fifth of mammals. And because of their wings, bats can be found all over the world, except for the Arctic, Antarctic, and some remote and isolated islands.

Bats often bear the notoriety of "sucking blood" due to their poor appearance and nocturnal appearance, but in fact, there are very few bats that feed purely on blood, and the feeding habits of most types of bats can be divided into carnivorous and herbivorous. Among them, carnivorous species prey on insects, a few predators on fish, frogs and other vertebrates, and herbivorous bat species feed on nectar, pollen, and fruits. Many of these bat species are capable of destroying insect pests such as mosquitoes in large numbers, while others can help pollinate plants.

And if we look at bats from the perspective of infectious disease risk, bats become living "petri dishes" – bats are known to carry at least 60 viruses and are natural hosts for a large number of zoonotic pathogens, including the smelly rabies, but bats rarely get sick themselves. What's more, these viruses have the opportunity to spread to other animals and even humans, and cross-infection between bats can lead to the emergence of new viruses and more easily break through our immune system.

What kind of "miraculous body",

Only so that the bats are "invulnerable"?

So the question is, why can bats carry so many viruses and be okay themselves?

There is a popular explanation that because bats are flying, the process raises body temperature. There seems to be some truth to this view, because "fever" is a common weapon of our immune system against pathogens - an increase in body temperature can inhibit the multiplication of many pathogens in our bodies.

However, in the case of bats, although the body temperature of bats is indeed relatively high when flying, the large wings of bats are densely vascular, which is an excellent heat dissipation device, which is why bats tend to wrap their wings around their bodies like "cloaks" when resting. And, because flying is quite energy-intensive, bats will also reduce their activity and go into a dormant state, at which point their body temperature may drop to a level similar to that of their environment, in which case won't the virus "take advantage of the situation"? What's more, many viruses are not so afraid of heat, and only rely on high body temperature to explain the "invincibility" of bats, which is not very convincing.

Bat resting hanging from a tree.

Recently, the leading academic journal Nature published an interesting paper that put forward a rather innovative idea: bats may be super immune because they can fly.

In this study, in order to better explain the secrets of bat immunity, a team co-led by Aaron Irving, a comparative immunologist at the University of Edinburgh United College of Zhejiang University, and Michael Hiller, an evolutionary geneticist at the Senckenberg Institute in Germany, used advanced sequencing and analysis techniques to obtain the genomes of 95 bat species. They then further compared the results with the previously completed bat genome data of 0 species, as well as the genomes of another 0 other mammals.

The comparison found that bats not only have more immune-related genes than other mammals, but these genes themselves also have some changes that help them better identify pathogens, regulate inflammatory responses, and respond to viral infections.

A prime example of this is the gene for ISG15, which is present in both bats and humans. The ISG0 gene in humans is a double-edged sword, it helps fight viruses on the one hand, but on the other hand, it can be dangerous if the body has a severe infection, which causes an excessively strong inflammatory response.

But bats have just the right mutations in their ISG15 gene—some of which increase bats' ability to fight viruses, while others make them safer. The study authors note that this allows bats to effectively block the virus without triggering the hyperinflammation that is common in humans.

Hypothesis: If you want to fly, you have to rely on immunity?

In the long journey of evolution, when did bats acquire these immune "superpowers"? Going back in time, researchers have found that the adaptive changes associated with immune genes can be traced back to the common ancestors of bats that learned to fly. This result suggests that there may be a connection between the bat's extraordinary immunity and its ability to fly.

At first glance, this conclusion is puzzling: Do you need strong immunity to take to the skies? That may be the case. Professor Owen thinks this may be because flying places a huge burden on the bat's body.

While flying, the bat's heart rate can be maintained at 1000 beats per minute for a long time. Extreme metabolism produces large amounts of toxic by-products such as reactive oxygen species. In order to cope with these "metabolic garbage", bat ancestors evolved the ability to fly and at the same time evolved a strong immune regulation ability. Inadvertently, these immunity makes them better able to tolerate deadly viral infections.

Of course, there are still some questions left unanswered in this study. For example, some molecular virologists have pointed out that although this theory sounds very reasonable, it is still only in the hypothesis stage after all, and it is difficult to really prove it. In addition, some of the current results still need to be further explained, such as the ability of different bat species selected by the researchers to inhibit the virus, although the ISG15 gene has the same key alteration, but these species still have differences in their ability to suppress the virus, suggesting that there are some other immune functions at work in some bat species that need to be further explored.

It is worth mentioning that the significance of the study is not limited to bats. Since most of the bat species selected by the researchers carry viruses that can be transmitted to humans, understanding how resistant bats are to viruses is not only expected to reduce the occurrence and spread of zoonotic diseases, but also provide valuable insights into the treatment of human diseases, such as helping to develop new drugs or regulating the human immune response. This will also be the future research direction of scientists.