It has spread across the globe in just a few short months, sickening hundreds of thousands, but the new coronavirus has the dubious distinction of not really being a living organism, biologists say.
"Viruses aren't considered alive -- in class, I call them pseudo-alive," said Eric Mendenhall, an associate professor of biological sciences at the University of Alabama in Huntsville.
"They require a host to even begin to function. However, since they use DNA or RNA to pass information to the next round of viruses the cell makes for them, they are subject to some of the same principles of evolution and selection that alive organisms are subject to," he explained in a university news release.
"A virus usually enters the cell through a protein our cells have on their surface. COVID-19 -- and SARS [severe acute respiratory syndrome] before that -- use a protein called ACE2, which is on the surface of the cells in our lung, throat and intestinal tract," Mendenhall said.
Coronaviruses are a category of viruses that typically infect mammals and birds; there were only six that could infect humans before COVID-19 showed up.
"Four cause mild symptoms, like a cold," Mendenhall said. "SARS was quite famous in 2003 but not seen since 2004, I believe, and MERS [Middle East respiratory syndrome], which is also deadly and is found in camels and infects people but doesn't spread very much, so it's not a huge concern. So, COVID-19 is the seventh coronavirus and the most deadly by far."
It's difficult to say why COVID-19 is so highly contagious.
"But being a new virus to us can play a role, as it will be the first time our immune system gets to see it and thus we don't have antibodies already made to defend ourselves," Mendenhall explained.
Viruses can't spread unless people help them, and people can stop the spread by washing hands and social distancing.
"If you don't pass it on, then that virus hits a dead end in its pseudo-life," Mendenhall said.
The World Health Organization has more on the coronavirus pandemic.