Acanthamoeba is a bacteriophage, a class of virus that infects bacteria. In this case, the bacterium is the amoeba. Acanthamoeba embeds itself in the amoeba and takes over the reproductive mechanism of the cell to make more viruses. Sputnik, however, is the first in a new class of viruses named virophages by the authors of the paper. Sputnik embeds itself in the DNA of Acanthamoeba, taking advantage of Acanthamoeba in the same way that virus takes advantage of its amoeba host. Once infected, an Acanthamoeba produces fewer new viruses. In effect, the virus gets sick.