Viruses, generally the most minuscule of parasites, apparently have to contend with vermin of their own. In August, infectious diseases physician Didier Raoult of the Université de la Méditerranée in Marseille, France, reported that he had discovered a tiny virus infecting another, a giant virus called Mamavirus. This unexpected type of attack suggests for the first time that one virus may influence the evolution of other viruses.
Raoult and his colleagues found Mamavirus in water taken from a cooling tower in Paris. The giant virus, a strain of the previously identified and slightly smaller Mimivirus, was found through microscopy to be infected by a 50-nanometer-wide virus. They named it Sputnik, after the first satellite to orbit Earth.
When the scientists cultured Mamavirus and Sputnik with an amoeba, they found that Sputnik forces Mamavirus to produce not just copies of Sputnik but fewer, and deformed, versions of itself. And when they sequenced Sputnik’s genome, they found its small ring of DNA contained genes from three different viral families, including Mamavirus.
The finding suggests that Sputnik infects more than one group of viruses and can shuttle genetic material from one giant virus to another. “This is a completely new way of transmitting genes,” Raoult says, and it could be driving evolution of new species in as-yet-unknown ways.
The discovery may also have practical applications. “We don’t have a good way to treat something like smallpox,” Raoult explains. “If it’s true that this virus is infecting other viruses, and if you are able to make it pathogenic for smallpox viruses—why not?”