A common asymptomatic infection caused by cytomegalovirus, which can produce life-threatening illnesses in the immature fetus and in immunologically deficient subjects. Cytomegalovirus is a member of the herpesvirus group, which asymptomatically infects 50–100% of the normal adult population. Such infections usually take place during the newborn period when the virus can be transmitted from the mother to the baby if the virus is present in the birth canal or in breast milk. Toddlers may also acquire the infection in nurseries. Later in life, the virus may be transmitted by heterosexual or male homosexual activity. After infection, cytomegalovirus remains latent in the body because it cannot be completely eradicated even by a competent immune system. It may be activated and cause illnesses when there is a breakdown of the immune system. Congenital or transplacental cytomegalovirus infection is also a fairly common event. With rare exceptions, it too is usually asymptomatic. Congenital cytomegalovirus disease results from transplacental transmission of the virus, usually from a mother undergoing initial or primary cytomegalovirus infection, during pregnancy. Its manifestations range from subtle sensory neural hearing loss detectable only later in life, to a fulminating multisystem infection and eventual death of the newborn. This important congenital disease occurs in about 1 in 1000 pregnancies. The only cytomegalovirus illness clearly described in mature, immunologically normal subjects is cytomegalovirus mononucleosis. This is a self-limited illness like infectious mononucleosis, the main manifestation of which is fever.Infectious mononucleosis Otherwise, cytomegalovirus illnesses are usually seen only when cellular immunity is deficient. They constitute the most important infection problem after bone marrow and organ transplantations. Manifestations vary from the self-limited cytomegalovirus mononucleosis to more serious organ involvement such as pneumonia, hepatitis, gastrointestinal ulcerations, and widespread dissemination. The virus causing these illnesses may come from activation of the patient's own latent infection, or it may be transmitted from an outside source, usually from latent cytomegalovirus infecting the graft from a donor. Cytomegalovirus illnesses are also serious, fairly frequent complications of the acquired immunodeficiency syndrome (AIDS). One reason is that most individuals with human immunodeficiency virus (HIV) infection are already infected with cytomegalovirus. Disease manifestations are similar to what is seen in transplant cases, except they may be more severe. Cytomegalovirus retinitis is a typical problem associated with advanced AIDS. Without treatment, the retina is progressively destroyed such that blindness of one or both eyes is inevitable.Acquired immune deficiency syndrome (AIDS) Cytomegalovirus diseases can be treated with two antivirals, ganciclovir or foscarnet, with varying degrees of success. Cytomegalovirus pneumonia in the bone marrow transplant recipient cannot be cured by antivirals alone because it probably has an immunopathologic component. Cytomegalovirus diseases in persons with AIDS can be contained but not cured by specific treatment. For example, ganciclovir treatment of cytomegalovirus retinitis is effective only as long as maintenance therapy is continued.Animal virus | 
