World's Largest Virus Discovered

The largest-known virus — both in terms of physical size and its genome — has been discovered and named, French researchers recently reported in the journal Science. It's one micrometer long, more than twice the size of the Megavirus, previously thought to be the largest virus at 440 nanometers. Most viruses are about 100 nanometers.

The new virus is called Pandoravirus — a chilling name because in mythology, Pandora's Box is the source of the world's evil. But the virus doesn't pose an immediate threat to human health, researchers said. "This is not going to cause any kind of widespread and acute illness or epidemic or anything," Eugene Koonin, an evolutionary biologist at the National Institutes of Health who specializes in viruses, told NPR Health.

Instead, this particular virus opens questions about the origins of life on earth. It's believed to have emerged from a type of cell that no longer exists, indicating that "the tree of life may need to be redrawn to account for these new viruses," researchers said in a Science press release.

Because Pandoraviruses seem completely like anything else currently on the planet, they could have originally come from another planet, like Mars, researchers told NPR. "At this point we cannot actually disprove or disregard this type of extreme scenario," he says.

So far, two different Pandoraviruses have been discovered. One, off the coast of Chile, and the other from a freshwater pond near Melbourne, Australia. The fact that this virus can live in salt or fresh water makes it even more fascinating, researchers said in the paper. Next, they're examining how the virus acts in the wild to understand how it affects ecosystems. Researchers also predicted that more and more giant viruses will be soon discovered.

Their massive size makes them first appear to be small bacteria. Bacteria are single-cell organisms that reproduce on their own, NPR Health explained, whereas viruses have to inject themselves into a larger cell to reproduce. Viruses are also typically too small to be seen with an ordinary microscope, whereas the "enormous" Pandoravirus can.

- weather.com