Rhadinoviruses are a genus of herpesviruses that include the Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), which causes Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman's disease. Other names for the Rhadinovirus genus include Rhadinoviridae and gamma-2 herpesviruses. The term rhadino comes from the Latin fragile, referring to the tendency of the viral genome to break apart when it is isolated. They are large double-stranded viruses that possess up to 100 genes in a single long chromosome which is flanked by repetitive DNA sequences called terminal repeats. Rhadinoviruses generally infect B lymphocytes and fibroblasts and once infection occurs, it is generally life-long. Rhadinoviruses have been found in New World monkeys such as the squirrel monkeys (herpesvirus saimiri) and in mice (murine gammaherpesvirus-68). More recently, both KSHV-like viruses and a new form of rhadinovirus called rhesus rhadinovirus have been discovered in Old World monkeys. These findings suggest that an additional human tumor virus related to KSHV may be found in humans.
Rhadinoviruses are unique because they have mastered the ability to pirate cellular genes from their host cells and incorporate them into their genomes. For example, most rhadinoviruses have a copy of the cyclin gene which regulates the ability of the cell to divide. These viruses tend to cause tumors when infection occurs outside of their native hosts or in the case of KSHV, in humans when the host is immunosuppressed due to AIDS, old age, or in the setting of organ transplantation.