The more bats are under stress, the greater is the risk from viruses

Bats have turned out to be the source of most zoonotic diseases that can infect human beings. The only flying mammals can host many different viruses without getting sick.

Be it the Nipah, Sars, Ebola, the Marburg virus or the recent novel coronavirus outbreak — all originated from bats. But why them?

A recent study at the University of California tried to find the reason behind bats being carriers of different viruses.

Bats are the only mammals that can fly. They need double the energy to cover the same distance that a rodent needs on ground. So bats have a high heart rate and metabolism.

This can lead to an accumulation of free radicals, a reactive molecule that can damage tissues. To prevent this reactive waste from damaging their cells and accelerate the ageing process, bats have evolved sophisticated defence mechanisms.

That is why some bats can live 40 years, whereas a rodent of the same size may live for two years. The same defensive mechanism helps the bats to defend themselves from deadly viruses and diseases. Whenever a virus starts attacking the cells of a bat, it produces a molecule called interferon-alpha. This molecule signals other cells to scale up their defence mechanism.

To overcome this defence, the virus starts to reproduce quickly and highly transmissible without harming the host bat. Although the bats can tolerate these viruses, it can be deadly to other mammals like humans.

Unlike bats, humans lack a fast-response immune system and the viral load becomes deadly. Also, the pathology of these viruses is new to the human immune system. That is why the death rates in zoonotic viral diseases are higher.

But bats can’t be blamed for the zoonotic disease outbreaks. Disturbing the natural habitat of bats and capturing them for meat can stress them. This increases the virus count in their saliva, urine and faeces, researchers said.