Definition
Virophages are small, double-stranded DNA viruses that require the co-infection of another virus. The co-infecting viruses are typically giant viruses. Virophages rely on the viral replication factory of the co-infecting giant virus for their own replication. One of the characteristics of virophages is that they have a parasitic relationship with the co-infecting virus. Their dependence upon the giant virus for replication sometimes results in reduced virulence of the giant viruses. Many virophage genomes are integrated into the genomes of single-celled eukaryotes, and they reactivate upon infection of a giant virus, thereby providing a form of inducible antiviral defense. The virophage may improve the recovery and survival of the host organism. Most known virophages are classified within the class Virophaviricetes and are associated with giant viruses of the family Mimiviridae. Virophages are associated with a range of other host viruses, however, including insect poxviruses.
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