CYTOMEGALOVIRUS (CMV)

Original Source: CENTERS FOR DISEASE CONTROL AND PREVENTION
WWW page: http://www.cdc.gov/dncidod/diseases/herpes/herpes.htm
Original Date: March 9, 1995
Copyright Restriction: Public Domain

GENERAL INFORMATION

Cytomegalovirus, or CMV, is found universally throughout all geographic locations and socioeconomic groups, and infects between 50 and 85% of adults in the United States by the age of 40. CMV is also the virus most frequently transmitted to a developing child before birth. CMV infection is more widespread in the developing countries and in areas of lower socioeconomic conditions. For most healthy persons who acquire CMV after birth there are few symptoms and no long term health consequences. Some persons with symptoms experience a mononucleosis-like syndrome with prolonged fever, and a mild hepatitis. Once a person becomes infected, the virus remains alive, but usually dormant within that person's body for life. Rarely does it cause recurrent disease unless the person's immune system is suppressed due to therapeutic drugs or disease. Therefore, for the vast majority of people, CMV infection is not a serious problem.

However, CMV infection is important to certain, high-risk groups. Major areas of concern are: (1) the risk of infection to the unborn baby during pregnancy, (2) the risk of infection to people who work with children, and (3) the risk of infection to the immunocompromised person, (meaning) organ transplant recipients, and HIV infected patients.

CHARACTERISTICS OF THE VIRUS

Cytomegalovirus is a member of the herpesvirus group, which includes herpes simplex virus type I and II, Varicella-Zoster virus, which is the virus that causes chicken pox, and Epstein-Barr virus which causes infectious mononucleosis. These viruses share a characteristic ability to remain dormant within the body over a long period of time. The initial infection, which is usually without symptoms, is always followed by a prolonged, inapparent infection during which the virus resides in cells without causing detectable damage or clinical illness. Although the factors controlling latency and reactivation are not completely understood, impairment of the body's immune system by medication or disease can consistently reactivate the virus.

Infectious CMV virus may be shed in the body fluids of any previously infected person, and is most likely to be found in urine, blood, saliva, tears, semen, and breast milk. The shedding of virus may take place intermittently, without any detectable signs, and without causing symptoms. Close or prolonged contact with a person shedding CMV is usually needed to acquire infection.

TRANSMISSION/PREVENTION

The modes of transmission of Cytomegalovirus from person to person are not completely understood. Infection appears to require close and intimate contact with a person excreting the virus in their saliva, urine, or other body fluids. CMV infection can be sexually transmitted, and can also be transmitted via breast milk, blood transfusions, and transplanted organs.

Although the virus is not highly contagious it has been shown to spread in households and day care centers. Transmission of the virus is often preventable, because it is most often transmitted through infected body fluids that come in contact with hands and then are absorbed through the nose or mouth of a susceptible person. Therefore, care should be taken when handling children and items like diapers. Simple hand washing is effective in removing the virus from the hands.

CMV infection without symptoms is common in infants and young children; therefore, infection during the early childhood years makes exclusion from schools or institutions unjustified and unnecessary. Similarly, hospitalized patients do not need separate or elaborate isolation precautions.

Screening children and patients for CMV is of questionable value. The cost and management of such procedures are impractical. Children known to have CMV should not be singled out for exclusion, isolation, or special handling. Instead, staff education and effective hygiene practices are advised in caring for all children.

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CIRCUMSTANCES WHEN CMV INFECTION COULD BE A PROBLEM

PREGNANCY

The incidence of primary (or first) CMV infection in pregnant women in the United States varies from 1% to 3%. Healthy pregnant women are not at special risk for disease from CMV infection. When infected with CMV, most women are without symptoms and only a few have a disease resembling mononucleosis. It is their developing unborn babies that may be at risk of developing congenital CMV disease. CMV remains the most important cause of congenital (meaning from birth) viral infection in the United States. For infants who are infected by their mothers before birth, two potential problems exist:

  1. Generalized infection may occur in the infant and symptoms may range from moderate enlargement of the liver and spleen (with jaundice) to fatal illness. With supportive treatment most infants with CMV disease usually survive. However, from 80% to 90% will have complications within the first few years of life that include hearing loss, vision impairment, and varying degrees of mental retardation.
  2. Another 5% to 10% of infants who are infected but without symptoms at birth will subsequently have varying degrees of hearing, visual, and mental or coordination problems.

However, these risks appear to be almost exclusively associated with women who have never been infected with CMV, and who are having their first infection with the virus. Even in this case two thirds of the babies will escape infection, and only 10% to 15% of the remaining third will have symptoms at the time of birth.

There appears to be little risk of CMV-related complications for women who have been infected at least six months prior to conception. For this group, which makes up 50% to 80% of the women of child bearing age, the rate of newborn CMV infection is 1% and these infants appear to have no significant illness or abnormalities.

The virus can also be transmitted to the infant at delivery from contact with genital secretions or later in infancy through breast milk. However, these infections usually result in little or no clinical illness in the infant.

To summarize, during a pregnancy when a woman who has never had CMV becomes infected with CMV, there is a potential risk that after birth the infant may have complications, the most common of which are associated with hearing loss, visual impairment, or diminished mental capabilities. On the other hand, infants and children who acquire CMV after birth have few, if any, symptoms or complications.

Recommendations for pregnant women with regard to CMV infection are as follows:

  1. Throughout the pregnancy, practice good personal hygiene, especially hand washing, after contact with diapers or oral secretions.
  2. Women who develop a mononucleosis-like illness during pregnancy should be evaluated for CMV infection and counseled about the possible risks to the unborn child.
  3. Recovery of CMV from the cervix or urine of women at or before the time of delivery does not warrant a cesarean section.
  4. Laboratory testing for antibody to CMV can be performed to determine if a women has already had CMV infection.
  5. The demonstrated benefits of breast-feeding outweigh the risk of acquiring CMV from the breast feeding mother.
  6. There is no need to either screen for CMV, or exclude children excreting CMV from schools or institutions, because the virus is frequently found in many healthy children and adults.

PEOPLE WHO WORK WITH INFANTS AND CHILDREN

For most healthy people working with infants and children there is no special risk from Cytomegalovirus infection. However, for women of childbearing age who previously have not been infected with CMV, there is a potential risk to the developing unborn child. (A thorough explanation of this risk is provided under the topic entitled pregnancy in this service.) Since CMV is transmitted through contact with infected body fluids, including urine and saliva, child care providers (meaning day care workers, special education teachers, therapists, as well as mothers) should be educated about the risks of CMV and the precautions they can take. Day care workers appear to be at a greater risk than hospital and other health care providers, and this may be due in part to the increased emphasis on personal hygiene in the health care setting.

Recommendations for individuals providing care for infants and children are as follows:

  1. Female employees should be educated concerning CMV, its transmission, and hygienic practices, such as hand washing, which minimize the risk of infection.
  2. Routine laboratory testing for CMV antibody in female workers is not recommended, but can be performed to determine her immune status.
  3. Susceptible nonpregnant women working with infants and children should not routinely be transferred to other work situations.
  4. Pregnant women working with infants and children should be informed of the risk of acquiring CMV infection, and the possible effects on the unborn child.

IMMUNOCOMPROMISED PATIENTS

While initial Cytomegalovirus infection can cause serious disease in the immunocompromised patient, the more common problem is the reactivation of the dormant virus. Infections by CMV are a major cause of disease and death in immunocompromised patients, including organ transplants recipients, patients undergoing hemodialysis, patients with cancer, patients receiving immunosuppressive drugs, and HIV-infected patients. Pneumonia, and an infection of the eyes called retinitis, appear to be the common manifestation of the disease. Due to the significant risk, the exposure of immunosuppressed patients to outside sources of CMV should be minimized. Whenever possible, patients who have never had CMV should be given organs and/or blood products that are free of the virus.

DIAGNOSIS

Most infections with Cytomegalovirus are not diagnosed because it usually produces few if any symptoms, and tends to reactivate intermittently without symptoms. However, persons who have been infected with CMV develop antibodies to the virus, and these antibodies persist in the body for the lifetime of that individual. A number of laboratory tests, which detect these antibodies to CMV, have been developed to determine infection, and are widely available from commercial laboratories. In addition, the virus can be cultured from specimens obtained from urine or throat swabs.

For diagnosing CMV, the following process may be helpful.

If a patient:
 
(1) has symptoms of infectious mononucleosis but has negative test results for mononucleosis and Epstein Barr virus, or,
(2) shows signs of hepatitis, but has negative test results for hepatitis A, B, and C,

then suspect and test for CMV.

For best diagnostic results, laboratory tests for CMV antibody should be paired. One should be taken upon suspicion of CMV, and another one taken within 2 weeks. A virus culture can be performed at any time the patient is symptomatic.

Laboratory testing for antibody to CMV can be performed to determine if a women has already had CMV infection. However, routine laboratory testing of all pregnant women is costly and the need for testing should therefore be evaluated on a case by case basis.

SEROLOGIC TESTING

To measure CMV antibody the enzyme immuno assay (or ELISA) is the most commonly available serologic test. The result can be used to establish acute infection, prior infection, or passively acquired maternal antibody in an infant.

Other tests include various fluorescence assays, indirect hemagglutination, latex agglutination, and complement fixation.

An ELISA technique for CMV-specific IgM is available, but may give false positive results unless steps are taken to remove rheumatoid factor or most of the IgG before testing the serum sample. Because CMV-specific IgM may be produced in low levels in reactivated CMV infection, its presence is not always indicative of primary infection. Only virus recovered from a target organ such as the lung provides unequivocal evidence that the disease is caused by acquired CMV infection. However, if paired tests show a demonstration of a fourfold rise in IgG antibody and a significant level of IgM, meaning equal to at least 30% of the IgG value, and/or virus excretion from a urine or throat specimen, then conclude that an active CMV infection is present.

CLINICAL DIAGNOSIS

For diagnosing CMV, the following process may be helpful.

If a patient:
 
(1) has symptoms of infectious mononucleosis, and has negative test results for mononucleosis and Epstein Barr virus, or
(2) shows signs of hepatitis, but has a negative test result for hepatitis A, B, and C,

then suspect and test for CMV by either virus culture or serologic test.

If serologic tests indicate a positive or high titer of IgG, do not automatically conclude that active CMV infection is present. However, if paired tests show either a rising titer of IgG or a significant level of IgM, meaning equal to at least 30% of the IgG value, then conclude that an active CMV infection is present.

TREATMENT

At the present time there is no treatment for CMV infection in the healthy individual. Potential antiviral drug therapy is now being evaluated in infants and in patients with depressed immunity, who have either sight or life-threatening illnesses. Vaccines are still in the research and development stage and are years away from widespread use.

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ADDITIONAL INFORMATION

The Biomedical Research Institute at the Children's Hospital in St. Paul Minnesota, has published a brochure titled CMV, Diagnosis, Prevention, and Treatment, 2nd Edition. This publication has been made available to CDC, and you may receive a copy by writing to:

Viral Exanthems and Herpes Virus Branch
M/S G18
CDC
Atlanta, GA 30333

or by calling (404) 639-3532.

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