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.