Some bacteriophages do not cause lysis or death of the host cell when they multiply. Instead, the phage DNA upon penetration into an E. coli cell gets integrated into the circular bacterial DNA. This becomes part of it and remains latent or inactive. The inserted phage DNA is now called a prophage.

ICTV-International Committee on Taxonomy of Viruses. It regulates the norms of classification and nomenclature of viruses. The ICTV scheme has only three hierarchical levels: The Family (including subfamilies), Genus and Species. The family names end with the suffix “viridae” while the genus names with “virus” and the species names are common English expressions describing their nature.