Cytomegalovirus

Definition

Cytomegalovirus (CMV) is a virus related to the group of herpes viruses. Infection with CMV can cause no symptoms, or can be the source of serious illness in people with weak immune systems. CMV infection is also an important cause of birth defects.

Description

CMV is an extremely common organism worldwide. It is believed that about 85% of the adult population in the United States have been infected by CMV at some point in their lives. CMV is found in almost all of the body's organs. It is also found in body fluids, including semen, saliva, urine, feces, breast milk, blood, and secretions of the cervix (the narrow, lower section of the uterus).

CMV is also able to cross the placenta (the organ that provides oxygen and nutrients to the unborn baby in the uterus). Because CMV can cross the placental barrier, initial infection in a pregnant woman can lead to infection of the developing baby.

Causes & symptoms

CMV is passed between people through contact with body fluids. CMV can also be passed on through sexual contact. Babies can be born infected with CMV, either becoming infected in the uterus (congenital infection) or during birth (from infected cervical secretions).

Like other herpes viruses, CMV remains inactive (dormant) within the body for life after the initial infection. Some of the more serious types of CMV infections occur in people who have been harboring the dormant virus, only to have it reactivate when their immune system is stressed. Immune systems may be weakened because of cancer chemotherapy, medications given after organ transplantation, or diseases that significantly lower immune resistance like acquired immunodeficiency syndrome (AIDS).

In a healthy person, initial CMV infection often occurs without symptoms and is rarely noticed. Occasionally, a first-time infection with CMV may cause a mild illness called mononucleosis. Symptoms include swollen glands, liver, and spleen; fever; increased white blood cells; headache; fatigue; and sore throat. About 8% of all mononucleosis cases are due to CMV infection. A similar infection, though slightly more serious, may occur two to four weeks after receiving a blood transfusion containing CMV.

In people with weakened immune systems, CMV infection can cause more serious and potentially life-threatening illnesses. These illnesses include pneumonia, and inflammations of the liver (hepatitis), brain (encephalitis), esophagus (esophagitis), large intestine (colitis), and retina of the eye (retinitis).

Babies who contract CMV from their mothers during birth rarely develop any illness from these infections. Infants born prematurely who become CMV infected during birth have a greater chance of complications, including pneumonia, hepatitis, and decreased blood platelets.

However, an unborn baby is at great risk for serious problems when the mother becomes infected with CMV for the first time while pregnant. About 10% of these babies will be born with obvious problems, including prematurity, lung problems, an enlarged liver and spleen, jaundice, anemia, low birth weight, small head size, and inflammation of the retina. About 90% of these babies may appear perfectly normal at birth. Unfortunately, about 20% of these babies will later develop severe hearing impairments and mental retardation.

Diagnosis

Body fluids or tissues can be tested to reveal CMV infection. However, this information is not always particularly helpful because CMV stays dormant in the cells for life. Tests to look for special immune cells (antibodies) directed specifically against CMV are useful in proving that a person has been infected with CMV. However, these tests do not give any information regarding when the CMV infection first occurred.

Treatment

Ganciclovir and foscarnet are both antiviral medications that have been used to treat patients with weak immune systems who develop a serious illness from CMV (including retinitis). As of 1998, research is still being done to try to find useful drugs to treat newborn babies suffering from congenital infection with CMV. Antiviral drugs are not used to treat CMV infection in otherwise healthy patients because the drugs have significant side effects that outweigh their benefits.

Prognosis

Prognosis in healthy people with CMV infection is excellent. About 0.1% of all newborn babies will have serious damage from CMV infection occurring while they were developing in the uterus. About 50% of all transplant patients will develop severe illnesses due to reactivation of dormant CMV infection. These illnesses have a high rate of serious complications and death.

Prevention

Prevention of CMV infection in the normal, healthy person involves good handwashing. Blood products can be screened or treated to insure that they do not contain CMV.

Key Terms

Cervix

The narrowed, lowest part of the uterus through which a baby must pass in order to enter the birth canal.

Congenital

A condition that exists before birth and at birth.

Placenta

The organ that provides oxygen and nutrition from the mother to the unborn baby during pregnancy. The placenta is attached to the wall of the uterus and leads to the unborn baby via the umbilical cord.

Further Reading

For Your Information

Books

• Corey, Lawrence. "Herpesviruses." In Sherris Medical Microbiology: An Introduction to Infectious Diseases, edited by Kenneth J. Ryan. Norwalk, CT: Appleton & Lange, 1994.
• Hirsch, Martin S. "Cytomegalovirus and Human Herpesvirus Types 6, 7, and 8." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.

  Periodicals

• Arribas, J. R., et al. "Cytomegalovirus Encephalitis." AIDS Weekly Plus (November 4, 1996): 30.
• Plis, Michael A., and Henry Masur. "Promising New Treatments for Cytomegalovirus Retinitis." Journal of the American Medical Association 273 (no. 18)(May 10, 1995): 1457+.
• Shelton, Brenda K. "Understanding Cytomegalovirus Infection." Nursing 25 (no. 1)(January 1995): 32.

  Organizations

• Centers for Disease Control and Prevention. (404) 332-4559. http://www.cdc.gov/ html.
• March of Dimes Birth Defects Foundation, National Office. 1275 Mamaroneck Ave., White Plains, NY 10605. http://222.modimes.org.
• National Congenital CMV Disease Registry. Texas Children's Hospital. MC 3-2371, 6621 Fannin St., Houston, TX 77030-2399. (713) 770-4387.

Gale Encyclopedia of Medicine. Gale Research, 1999.