Viruses are world champion parasites—think of all the trouble they give us, from Ebola to HIV. Now French researchers have discovered a viral first … a virus that infects another virus.

A virus that scientists are calling Sputnik was found in a newly discovered strain of so-called mimivirus, which is the  world's largest known virus. Virologist Jean-Michel Claverie, of France's National Center for Scientific Research and a team from the University of the Mediterranean in Marseille, happened upon the strain of mimivirus swimming in the water of a Parisian cooling tower. When they peeked inside the viral particle, they discovered Sputnik, which consists of only 21 genes.

They found that mimiviruses infected with Sputnik are less effective at infecting amoebae, which is what they normally do.

The researchers believe that Sputnik is the first of a yet-to-be-discovered family of viruses that they suspect may plague large viruses that attack ocean plankton. The French team reported their findings in the new issue of Nature, out yesterday.

The finding may answer a long-standing debate posed upon a 2004 cover of Scientific American: Are viruses alive?

It’s a seemingly simple question, but actually not: On the one hand, viruses can copy themselves and affect the health and behavior of other organisms. But, they require the machinery of other organisms to do any of that.

But, according to Claverie, if mimivirus can both pirate another organism's DNA-copying machinery and fall prey to another virus that does the same to it, then mimivirus is most certainly alive.

"There’s no doubt this is a living organism," he told Nature News. "The fact that it can get sick makes it more alive."

(Photo: iStockphoto/Henrik Jonsson)