A recent article in the Proceedings of the National Academy of Sciences discussed the discovery of a bacteria whose only diet is viruses; hence the name virovore. Actually, the scientific one is Halteria ciliate.
These bacteria were first discovered in fresh water ponds. In the lab, each Halteria organism consumed 1 million viruses daily, but when studied in their natural element they consumed 1 quadrillion viruses daily. Since Halteria do not seem to be pathogenic to humans there is ongoing research to see if there might be a way to use Halteria as a treatment for human viral infections.