Cytomegalovirus is a genus of viruses in the order Herpesvirales, in the family Herpesviridae, in the subfamily Betaherpesvirinae. Humans and monkeys serve as natural hosts. The eightspecies in this genus include the type species, Human betaherpesvirus 5, which is the species that infects humans. Diseases associated with HHV-5 include mononucleosis, and pneumonia. In the medical literature, most mentions of CMV without further specification refer implicitly to human CMV. Human CMV is the most studied of all cytomegaloviruses.
Taxonomy
Within the Herpesviridae, CMV belongs to the Betaherpesvirinae subfamily, which also includes the genera Muromegalovirus and Roseolovirus. It is also related to other herpesviruses within the Alphaherpesvirinae subfamily, which includes herpes simplex viruses 1 and 2 and varicella-zoster virus, and the Gammaherpesvirinae subfamily, which includes Epstein–Barr virus and Kaposi's sarcoma-associated herpesvirus. Several species of Cytomegalovirus have been identified and classified for different mammals. The most studied is human cytomegalovirus, which is also known as human betaherpesvirus 5. Other primate CMV species include chimpanzee cytomegalovirus that infects chimpanzees and orangutans, and simian cytomegalovirus and Rhesus cytomegalovirus that infect macaques; CCMV is known as both panine beta herpesvirus 2 and pongine betaherpesvirus 4. SCCMV is called cercopithecine betaherpesvirus 5 and RhCMV, Cercopithecine betaherpesvirus 8. A further two viruses found in the night monkey are tentatively placed in the genus Cytomegalovirus, and are called herpesvirus aotus 1 and herpesvirus aotus 3. Rodents also have viruses previously called cytomegaloviruses that are now reclassified under the genus Muromegalovirus; this genus contains mouse cytomegalovirus is also known as murid betaherpesvirus 1 and the closely related Murid betaherpesvirus 2 that is found in rats.
Species
The genus consists of these 11 species:
Aotine betaherpesvirus 1
Cebine betaherpesvirus 1
Cercopithecine betaherpesvirus 5
Human betaherpesvirus 5
Macacine betaherpesvirus 3
Macacine betaherpesvirus 8
Mandrilline betaherpesvirus 1
Panine betaherpesvirus 2
Papiine betaherpesvirus 3
Papiine betaherpesvirus 4
Saimiriine betaherpesvirus 4
Structure
Viruses in Cytomegalovirus are enveloped, with icosahedral, spherical to pleomorphic, and round geometries, and T=16 symmetry. The diameter is around 150–200 nm. Genomes are linear and nonsegmented, around 200 kb in length.
All herpesviruses share a characteristic ability to remain latent within the body over long periods. Although they may be found throughout the body, CMV infections are frequently associated with the salivary glands in humans and other mammals.
Cytomegalovirus was first observed by German pathologist Hugo Ribbert in 1881 when he noticed enlarged cells with enlarged nuclei present in the cells of an infant. Years later, between 1956 and 1957, Thomas Huckle Weller together with Smith and Rowe independently isolated the virus, known thereafter as “cytomegalovirus”. In 1990, the first draft of human cytomegalovirus genome was published, the biggest contiguous genome sequenced at that time. In January 2020, scientists at Rockefeller University led by Jean-Laurent Casanova discovered that there may be a link between a deficiency in nitric oxide synthase 2 and fatal cases of CMV. This finding may lead to new treatments for patients with CMV and new genetic screening approaches to discover those who are vulnerable to the virus due to a deficiency in NOS2.
