Scientists have long suspected that the rate of new infectious diseases could accelerate, especially in developing countries where human and animal interaction is increasing.

Changes in the environment are driving displaced species of animals into new habitats, allowing them to mix with other species or potential hosts.

Those shifts, combined with greater human interaction with animals as people move deeper into forests, increases the chances of a virulent virus jumping species.

This kind of spillover, when a pathogen in one species could start circulating in another and potentially create a new disease - is what appears to have happened in China with the virus that causes COVID-19. Like many infectious viruses introduced this way, the outbreak started with bats.

Many deadly viruses in the past have originated from bats including the deadly Ebola outbreaks in Western Africa. Nipah, also carried by bats, has already caused human outbreaks across South and South East Asia and has "serious epidemic potential", according to global health and infectious disease specialists.

The coronavirus family of viruses also includes diseases such as Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). Scientists have discovered that SARS and MERS were caused by viruses that originated in bats, with other animals serving as intermediate hosts.

Why bats?

Bats are a group of flying mammals, with more than 1,300 species in 20 families, according to IUCN. They make up approximately 20% of all mammal species and are found all over the world except for the Arctic, the Antarctic and a few oceanic islands.

Bats first appear in the fossil record roughly 50 million years ago and represent the third group of flying vertebrates in Earth's history, after the flying reptiles called pterosaurs and birds.

The only other group coming close to harbouring as many viruses are rodents, the most diverse group of mammals. There are approximately 2,300 species of rodents in 33 families, making up about 40% of all mammals. Rodents are believed to harbour more viruses as a group but bats harbour more viruses per species.

The diversity of both groups has been seen by scientists as a possible mechanism for driving virus diversity, as the greater number of species can create more potential niches for viruses. [...]

Studies have shown that bats are unique when it comes to hosting zoonotic viruses even when compared to rodents, as bats host more zoonotic viruses per species than rodents do.