The probability that a spillover will occur depends on many biological and social factors, including the rate and severity of animal infections, environmental pressure on the disease to evolve and the amount of close contact between infected animals and people.
WHY SPILLOVER MATTERS
While not all animal viruses or other pathogens are capable of spilling over into people, up to three-quarters of all new human infectious diseases have originated from animals. There’s a good chance the next big pandemic risk will arise from spillover, and the more that’s known about how spillovers occur, the better chance there is at preventing it.
Most spillover research today is focused on learning about and preventing viruses – including coronaviruses, like the one that causes COVID-19 and certain viral lineages of avian influenza – from jumping into humans. These viruses mutate very quickly, and random changes in their genetic code could eventually allow them to infect humans.
Spillover events can be hard to detect, flying under the radar without leading to bigger outbreaks. Sometimes a virus that transfers from animals to humans poses no risk to people if the virus is not well adapted to human biology. But the more often this jump occurs, the higher the chances a dangerous pathogen will adapt and take off.
SPILLOVER IS BECOMING MORE LIKELY
Epidemiologists are projecting that the risk of spillover from wildlife into humans will increase in coming years, in large part because of the destruction of nature and encroachment of humans into previously wild places.
Because of habitat loss, climate change and changes in land use, humanity is collectively jostling the table that is holding up that cup of water. With less stability, spillover becomes more likely as animals are stressed, crowded and on the move.
As development expands into new habitats, wild animals come into closer contact with people – and, importantly, the food supply. The mixing of wildlife and farm animals greatly amplifies the risk that a disease will jump species and spread like wildfire among farm animals.
