CMV (Cytomegalovirus) Infection
CMV (Cytomegalovirus) Infection
Cytomegalovirus (si-to-MEG-a-lo-vi-rus), or CMV, is one of the most common viruses infecting human beings. In healthy people, it rarely causes any symptoms. CMV infection is mainly of concern in persons who have weakened immunity, such as organ transplant recipients and those with HIV/AIDS. Some babies born with CMV infection, transmitted in the womb, may go on to suffer from severe health problems.
CMV belongs to the herpes family of viruses, all of which exist as viral particles of diameter around 200 nm, consisting of a protein exterior enclosing a molecule of double-stranded DNA. Other significant herpes viruses include the herpes simplex viruses, varicella-zoster virus (which causes chicken pox), and Epstein-Barr virus. CMV may lie dormant in white blood cells for many years, but the infection can be re-activated at any time. CMV cannot be eliminated, but symptoms of active infection can be treated with antiviral drugs, and there is also research on a preventive vaccine.
CMV infects cells called fibroblasts, which are found in skin and connective tissue, and white blood cells. In most people, the infection lies dormant. Some people may experience symptoms similar to those of mononucleosis— fever, swollen glands, fatigue, and sore throat. These symptoms occur in many other conditions, however, so it is difficult to determine that CMV is responsible.
For people with weakened immunity, CMV can become a serious problem because the virus is no longer held in check. Those with HIV/AIDS may experience complications such as retinitis, an eye infection that can lead to blindness. CMV may also cause potentially fatal pneumonia among organ transplant recipients because they take immunosuppressant drugs to protect the new organ. Another group at risk of CMV infection includes newborns, who may become infected in the womb. Congenital (present at birth) CMV infection can lead to many problems, including deafness and mental retardation, some of which may not become apparent until the child gets older.
Transmission of CMV is by contact with infected body fluids such as blood, semen, vaginal fluid, tears, urine, and saliva, although the infection is not spread by casual contact. A woman can transmit CMV to her baby through the placenta, while still in the womb, by exposure to cervical fluids during childbirth, or through breast milk. Infected children shed the virus in urine and other fluids for years and may transmit the infection horizontally to other children and adult caregivers in a nursery group setting.
WORDS TO KNOW
ANTIBODY: Antibodies, or Y-shaped immunoglobulins, are proteins found in the blood that help to fight against foreign substances called antigens. Antigens, which are usually proteins or polysaccharides, stimulate the immune system to produce antibodies. The antibodies inactivate the antigen and help to remove it from the body. While antigens can be the source of infections from pathogenic bacteria and viruses, organic molecules detrimental to the body from internal or environmental sources also act as antigens. Genetic engineering and the use of various mutational mechanisms allow the construction of a vast array of anti-bodies (each with a unique genetic sequence).
CONGENITAL: Existing at the time of birth.
FIBROBLAST: A cell type that gives rise to connective tissue.
HORIZONTAL TRANSMISSION: Horizontal transmission refers to the transmission of a diseasecausing microorganism from one person to another, unrelated person by direct or indirect contact.
IMMUNOSUPPRESSED: A reduction of the ability of the immune system to recognize and respond to the presence of foreign material.
SHED: To shed is to cast off or release. In medicine, the release of eggs or live organisms from an individual infected with parasites is often referred to as shedding.
The prevalence of CMV worldwide is between 40% and 100% of all people infected, with those in less developed countries and of lower socioeconomic status being more at risk. In the United States, 50–80% of adults are infected with CMV by the time they are 40 years of age. One percent of newborns shed CMV in their urine, which indicates they have been infected, but 90% of them remain healthy. The rest may develop serious ongoing health problems.
CMV infection is widespread, but is generally contained by the immune system. If this begins to break down, then infection will take hold, which is why HIV/AIDS patients and organ transplant recipients are also at risk of infection, as they are from many other normally harmless microbes, such as Candida.
CMV does not respond to the antiviral drug acyclovir, but is sensitive to a closely related drug called ganciclovir, which has been shown to reduce the complications of CMV-induced mortality among immunosuppressed persons (persons with weakened immune systems, either through disease or deliberate medical treatment). Foscarnet is another antiviral drug that is used in the treatment of CMV retinitis in HIV/AIDS. Cidofovir, the other drug for CMV infection, can be used to protect people with HIV/AIDS and organ transplant recipients from episodes of infection.
Normal hygiene and precautions are currently the best way of preventing CMV infection; the drugs are too toxic to give to pregnant women. Vaccines for CMV are being developed and these could play a vital role in reducing infection among newborns.
Congenital CMV infection is more common than other well-known congenital conditions such as Down syndrome, fetal alcohol syndrome, and neural tube defects. But only around 20% of those born with CMV will develop complications such as deafness, blindness, liver failure, and seizures. Those whose mothers become infected for the first time during pregnancy are most at risk of having babies with health problems. Scientists assume this is because there are no CMV antibodies present in the maternal blood supply to protect the fetus.
In the United States, 1–4% of women develop such primary infections during pregnancy and one-third of these pass on the infection in the womb. Pregnant women and babies could benefit most from a vaccine against CMV.
IN CONTEXT: EFFECTIVE RULES AND REGULATIONS
With regard to CMV infection, the Division of Viral and Rickettsial Diseases at Centers for Disease Control and Prevention (CDC), states the following:
- “CMV infection is very common in day care settings, but CMV usually does not harm the children who become infected. Adults who have not had CMV and who work with children in day care, especially children 1 to 2 years of age, are at high risk for CMV infection. Such adults face little risk of getting seriously sick from CMV infection. However, pregnant women who become infected with CMV are at high risk of passing the infection to their fetuses.”
- “Pregnant mothers who have young children in day care or who work in day care centers can help prevent getting infected with CMV by practicing good hygiene (such as handwashing). They should also avoid direct contact with saliva through behaviors such as kissing young children on the lips.”
- “Since CMV is spread through contact with infected body fluids, including urine and saliva, child care providers (meaning day care workers, special education teachers, therapists, and mothers) should be educated about the risks of CMV infection and the precautions they can take. Day care workers appear to be at a greater risk of becoming infected with CMV than hospital and other health care providers, and this may be due in part to the increased emphasis on personal hygiene (such as handwashing) and the lower amount of personal contact in the health care setting.”
- “Non-pregnant women of childbearing age who have never been infected with CMV and who are working with infants and children should not be routinely moved to other work situations to avoid CMV infection.”
- “Pregnant women working with infants and children should be informed of the risk of getting CMV infection, the possible effects on the unborn child, and appropriate prevention strategies.”
- “Routine laboratory testing for CMV antibody (immune protein) in female workers is not currently recommended. However, female workers who are pregnant or planning a pregnancy should be informed that a CMV antibody test can help them assess their risk. Whenever possible, CMV seronegative (without CMV antiobodies) pregnant women should consider working in a setting with less exposure to young children.”
Tan, James S. Expert Guide to Infectious Diseases. Philadelphia: American College of Physicians, 2002.
Centers for Disease Control and Prevention (CDC). “Cytomegalovirus (CMV).” February 6, 2006 <http://www.cdc.gov/cmv/> (accessed May 1, 2007).