A commonly occurring virus of the herpes virus group – the name derived from the swollen appearance of infected cells (‘cytomegalo’ = large cell). The infection is usually asymptomatic (or like mild inﬂuenza), but it can cause an illness similar to infectious MONONUCLEOSIS. Most people (80 per cent) will have had CMV infection by the time they are adults, but the virus can remain latent in the body and cause recurrent infections. During an acute infection the virus is excreted in saliva, breast milk and urine as well as from the vagina, and this may continue for years. CMV is transmitted naturally by saliva or during sexual contact, but blood transfusions and organ transplantations are also infection routes. Although CMV rarely causes its host any problems, when it is passed from an infected mother to her fetus in utero or to an infant during birth (from vaginal secretions) or via breast milk postnatally, the virus causes a generalised severe infection in the infant. This can involve the central nervous system and liver, causing death of the fetus or neonate. If the infant survives it may be mentally retarded, with motor disabilities, deafness and chronic liver disease. In England and Wales about 400 babies a year are born with CMV-induced disabilities. If an adult is immunodeﬁcient (see IMMUNODEFICIENCY) because of HIV infection/AIDS or as a result of immunosuppressive treatment after an organ transplant, he or she may become seriously ill.
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