Think about the type of animal that would make an ideal host for a virus. It would gather in large dense groups, making it easier for the virus to jump into fresh hosts. It should have a relatively long lifespan, so any single individual has many chances of becoming infected. It would certainly travel over long distances to spread the infection far and wide. Humans certainly fit the bill. So do bats.

At least one in every five mammal species is a bat. These diverse fliers—all 1,200 species of them—are reservoirs for an equally diverse group of viruses, including many deadly celebrities that can jump into humans. Bats carry rabies. They harbour SARS and other coronaviruses. They’ve got Nipah virus