Pandemics can begin in many ways. A wild animal could infect a hunter, or a farm animal might spread a pathogen to a market worker. Researchers in a lab or in the field could be exposed to viruses and unwittingly pass them to others. Natural spillovers and accidents have been responsible for every historical plague, each of which spread from a single individual to afflict much of humanity. But the devastation from past outbreaks pales in comparison to the catastrophic harm that could be inflicted by malicious individuals intent on causing new pandemics.
Thousands of people can now assemble infectious viruses from a genome sequence and commercially available synthetic DNA, and numerous projects aim to find and publicly identify new viruses that could cause pandemics by characterizing their growth, transmission, and immune evasion capabilities in the laboratory.