People rarely hear about cytomegalovirus (CMV) because, even though it's very common, it seldom causes illness. Most people become infected before they reach three years of age. The immune system of a healthy person may not prevent CMV from infecting the body, but it normally does inactivate the virus and confine it to a dormant state throughout a person's life. If CMV is acquired for the first time later in a person's life, it can cause a brief mononucleosis-like illness. CMV's greatest threat is to immune-deficient patients and to babies whose mothers are infected during early pregnancy.

Transmission

CMV is present in nearly all human body fluids, particularly urine, saliva, semen, breast milk, and blood. It is commonly transmitted in day-care centers, where the children and staff members come into contact with infected children's saliva or urine-soaked diapers. The virus then can be carried from unwashed hands or shared toys to the mucosal tissue of the mouth or nose. CMV also can be transmitted from one sexual partner to another. A woman can transmit the virus to her baby before it is born or at delivery, through contact with cervical fluids. In addition, it is possible to acquire CMV from transfused blood or transplanted organs.

Immune-Deficient Patients

A person undergoing organ transplantation or cancer chemotherapy must take drugs that suppress the immune system. If the patient had become infected with CMV earlier in life, the now weakened immune system allows the previously dormant virus to reactivate, resulting in life-threatening illness. In someone who is already taking immune-suppressant drugs when first exposed to the virus, the new infection can cause severe illness. Similarly, in patients with immune-deficiency diseases such as AIDS, CMV can cause pneumonia, hepatitis, encephalitis (brain inflammation), colitis, and a serious eye infection called retinitis.

Effects on Babies

CMV infection is of concern if a woman is in early pregnancy when she is first infected with the virus. Some of the babies born to these women may eventually develop minor impairments affecting hearing, vision, or mental capacity. A small percentage of the babies are born with severe neurological damage, including mental retardation or profound hearing loss. Prenatal tests of amniotic fluid can offer some evidence that fetal infection may have occurred.

CMV Mononucleosis

While CMV infection occurs uneventfully in most people, it can sometimes cause an acute form of mononucleosis. The symptoms include fever that lasts two to three weeks, hepatitis, and occasionally a rash. CMV mono is a self-limiting disease and, for people who do not have a serious immune deficiency, the prognosis is excellent.

Diagnosis

Results of tests for CMV can be misleading. The current tests, which detect immune cells in the blood called antibodies, indicate only that a person has been infected at some point in life. If a patient has symptoms that suggest a recently acquired CMV infection, a doctor may do sequential tests, in which changes in antibody levels may indicate active infection. Since those changes can be hard to distinguish from normal fluctuations, researchers are working to develop tests that will be more specific. However, in immune-deficient patients, the tests can be useful for measuring the effectiveness of therapy, and CMV screening in newborns can identify potential problems, such as a hearing defect. Researchers are now refining rapid and inexpensive tests that screen for CMV in saliva.

Treatment

Two antiviral drugs, ganciclovir and foscarnet, now are available for treating CMV infection (such as retinitis) in immune-deficient patients. Such treatment is not recommended for people with healthy immune systems because the risk from disease is small compared with the side-effects of the drugs.

Prevention

Good hygienic practices such as hand washing, especially in day-care settings, can reduce the risk of transmission. However, intensive infection-control measures generally are not practical in dealing with a virus as common as CMV. A preventive vaccine is in early stages of development.

Information provided by NIH

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