The virus named for giant cells carries one of the longest human-virus genomes
Cytomegalovirus takes its name from Greek words for a big container, after the swollen cells a German pathologist spotted in an infant in 1881. Its human strain packs roughly 235,000 DNA letters coding for at least 208 proteins, and like every herpesvirus it can hide in the body for years.
Hugo Ribbert noticed those oversized cells, with enlarged nuclei, in 1881. Isolating the culprit took until 1956 and 1957, when Thomas Huckle Weller and, separately, Smith and Rowe grew the virus and gave it the name that stuck. In 1990 a first draft of the human strain's genome appeared, then the largest continuous genome ever sequenced.
The genus belongs to the herpesvirus order and contains 11 species, most infecting primates: chimpanzees, orangutans and macaques each have their own. The one that infects people, human cytomegalovirus, is also catalogued as human herpesvirus 5, and it sits in the same subfamily as the viruses behind roseola, while cousins further out include herpes simplex, chickenpox and Epstein–Barr. Viral particles are enveloped and roughly 150 to 200 nanometres across. Wild-type human strains have a double-stranded DNA genome longer than any other human herpesvirus, organised into long and short unique stretches flanked by inverted repeats.
Spread depends on contact with bodily fluids such as saliva and urine. Once inside, the virus can lie latent for long periods, and infections often centre on the salivary glands. In humans it is associated with mononucleosis and pneumonia, and infection passed on before birth can cause defects affecting the eyes, ears, liver and spleen. A review of four years of antibody tests at Bhutan's national referral hospital found cytomegalovirus and herpes simplex the most frequently detected of a group of pregnancy-related infections.
The virus has also become a laboratory tool. A stretch of its DNA called the CMV promoter strongly and continuously switches on whatever gene follows it, so genetic engineers routinely build it into vectors for work in mammalian cells.
Source: Cytomegalovirus
