Created: July 15, 2020 02:24 PM
Scientists think the pandemic virus originally arose in bats, which carry many kinds of coronaviruses without apparent harm.
The virus jumped from bats to humans, perhaps with some other animal acting as middleman.
To become a pandemic threat, the virus needed both to infect people and to spread easily between them. Those two abilities don't always coincide. Some flu viruses from birds can infect people but not spread person to person, for example.
The coronavirus gained those abilities through mutations, genetic changes it picked up by chance as it replicated itself. Viruses mutate constantly. Most changes don't help a virus infect its target animal and may even reduce its ability to do that. These hindering mutations are usually weeded out over time.
But in rarer circumstances, a virus happens to mutate in a way that does help it infect its target.
For the pandemic virus, key mutations happened in a spike-like protein the virus uses to attach to cells it infects. Originally, that spike was best suited to grab onto bat cells. But mutations made it more suited to infecting human cells. Those changes didn't necessarily happen after the virus entered the human population. So they may have happened while the virus dealt with some other species after leaving bats.
Scientists don't know when the virus gained the ability to spread easily between people. It may have happened even before it infected its first human victim, so it was able to take off in the human population right away. That's often the case in flu pandemics, at least to some degree.
A less likely possibility is that it wasn't very contagious when it infected that first person. But it picked up additional mutations in that person, or as it inefficiently infected others. Eventually, with the help of natural selection, it would have gained its full collection of changes that gave it pandemic power.
Scientists may never discover whether the coronavirus was already equipped to wreak havoc before it entered the human population. They could find out if they recovered samples from the very first person infected. But that chances of identifying that person and getting samples are very low.
The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute's Department of Science Education. The AP is solely responsible for all content.
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