Why Bats Don't Get Sick- But We Do

Ebola, rabies, SARS, and COVID-19 are not just viral diseases — they are zoonotic diseases, meaning they’re caused by viruses transmitted from animals to humans. While many animals can be carriers, one stands out as a viral “super host”: bats.

So what makes these creatures of the night the perfect breeding ground for viruses? Bats harbor significantly more zoonotic viruses than other mammals. Researchers have identified over 60 different types circulating in bat populations, and on average, each bat hosts nearly two of these viruses. Some of them are linked to major outbreaks like MERS, SARS, and Ebola — diseases that spread to humans either directly from bats or through intermediate animals.

Scientists have also suggested that bats may be connected to the coronavirus responsible for COVID-19. But with such a heavy viral load, how do bats manage to stay healthy?

The secret seems to lie in their ability to fly. Flying requires intense physical effort — flapping their wings hundreds of times per minute causes significant cellular damage, the kind that usually triggers a strong immune response. In humans, this would result in inflammation, fever, or mucus production. While these symptoms are meant to protect the body, an overreaction of the immune system can lead to severe conditions like pneumonia, as seen in serious COVID-19 cases.

However, bats have evolved to avoid this. Their immune systems have adapted to minimize inflammation, producing only a mild response that allows them to fly without overwhelming their bodies. This balance gives them a unique advantage: the ability to live with many viruses without getting sick.

And there’s more — unlike other mammals, which must “turn off” their antiviral defenses to avoid excessive inflammation, some bat species keep their antiviral response constantly active. In other words, their immune system is always on alert, ready to fight off invading viruses. They don’t necessarily kill the virus, but they protect their cells, making them perfect viral incubators — coexisting with viruses just enough to survive.

Bats make up about 20% of all mammal species, and they’re very social animals, which helps viruses spread easily among them. They can also travel great distances in short periods of time, extending their geographic reach — and with it, their viral transmission range. Through their saliva, feces, or urine, viruses can spread to other animals and humans, especially when bats are handled, hunted, butchered, or eaten.

That’s exactly what happened in 2002, when a horseshoe bat infected a civet, which then passed the SARS virus to humans.

But before we start blaming bats, we need to remember their value. Bats play a vital role in ecosystems: they control insect populations, pollinate crops, and even inspired sonar technology. Without bats, we wouldn’t have tropical rainforests as we know them.

So while it’s true that bats may carry viruses capable of infecting humans, the real issue lies in human behavior. Most zoonotic outbreaks are not the fault of animals, but of how humans interact with wildlife. Expanding cities and farms into wild areas, cutting down forests, and capturing or trading wild animals all increase the chances of viruses jumping to humans.

COVID-19 wasn’t the first — and it won’t be the last — pandemic caused by a zoonotic disease. But it can serve as a warning. We need to keep investing in public health measures, strengthen healthcare systems in vulnerable countries, and continue researching what viruses pose risks to humans. We must also identify the behaviors and activities that increase our exposure, so we can work with local communities and governments — including in the U.S. — to reduce those high-risk actions.