What is cytomegalovirus?
Cytomegalovirus, often known as CMV, is a member of the chickenpox family of viruses. It is extremely ubiquitous in the population and affects people of all ages. In the U.S. 1/3 of children have been infected by age 5 and over 50% of adults have been infected by age 40. Most people infected with the virus have no symptoms and are not aware they have been infected. Some people develop mild illness that may include fever, sore throat, fatigue, and swollen glands. People with weakened immune systems may develop more serious symptoms.
Once in the body, the virus stays for life and can reactivate at a later time. On occasion, a person can also become infected with a different strain of the virus.
Unlike chickenpox (varicella), there is no vaccine for CMV. Since most infections have no or very mild symptoms, treatment for an infection is not required. Treatment with antiviral medications is only approved for by the FDA for patients with immunodeficiency or who have had organ transplants.
How is CMV transmitted?
- By direct contact with an infected person’s urine or saliva (most commonly from an infant or young child)
- Across the placenta in pregnancy
- From mother’s vaginal secretions at time of birth of an infant
- Through breast milk (note: women who are infected with CMV can breastfeed healthy infants born at full term since healthy infants and children who acquire CMV after birth generally have few, if any, symptoms from the infection)
- From infected transplanted organs and blood transfusions
What is Congenital CMV?
This refers to a CMV infection acquired by the fetus in pregnancy. The mother transmits the virus to the fetus via the placenta during pregnancy or to the newborn via vaginal secretions at delivery.
Approximately one of 150 infants are born with congenital CMV infection. The risk of transmission of CMV to a fetus is highest when the mother’s first ever CMV infection (primary infection) occurs during a pregnancy.
In the U.S., 1 to 4% of women will have their primary infection during pregnancy. In this situation, the risk of transmission of CMV to the fetus is 30 to 40%, with the highest chance of transmission in the third trimester. However, the most serious consequences to the fetus occur when infection is transmitted in the first trimester. Of the fetuses infected in the uterus after a primary maternal infection, approximately 10% will show symptoms at birth. About half of these children will have longer term problems. Fortunately, the majority of babies will never show symptoms of CMV nor have any health problems.
If a woman has a reactivation of the dormant virus as opposed to a primary infection, the risk of transmission to her fetus is only 0.15 to 2%.
Signs and Symptoms of Congenital CMV Infection at Birth
Birth may occur prematurely.
Signs at birth, even at term, may include:
- Small size of the newborn
- Small head size
- Seizures
- Medical problems with the lungs, liver, and spleen
Diagnosis of congenital CMV can be confirmed by lab testing of the newborn’s saliva, urine, or blood collected within 2 to 3 weeks of birth.
Long Term Problems Associated with Congenital CMV
These may include any or all of the following:
- Small head size
- Hearing loss
- Vision loss
- Lack of coordination
- Muscle weakness
- Seizures
- Delayed development and intellectual disability
Who is at highest risk of transmitting CMV to a fetus?
A pregnant woman who has never been infected with CMV and who already has an infant or small child, or who works with infants and children (e.g. in a day care center) is at high risk of contracting CMV from an infected child’s saliva or urine. Remember, most children with an active CMV infection show no symptoms or may have mild symptoms resembling the common cold. If the pregnant woman contracts the infection, she now has a primary infection and may transmit it to her unborn child.
What can be done to Minimize Transmission of CMV in Pregnancy?
Since there is no vaccine for CMV, and it is so common, there is no guaranteed way of preventing a pregnant woman from contracting it.
A woman can choose to have a blood test for the CMV IgG antibody prior to conception. If this is highly positive, it means she has been exposed to the virus at some point in her life and unless she has a reactivation of this or is infected with another strain of CMV, she is less likely to pass the virus to her fetus.
If on blood testing she is negative for the CMV IgG antibody, it means she has not been exposed and is more susceptible to becoming infected during her pregnancy.
However, all pregnant women should take precautions to reduce their risk of exposure to the virus and to minimize the chance of transmission to the fetus. These precautions include:
- Avoid kissing small children on the mouth to reduce contact with saliva
- Do not share food with a child or eat off a child’s plate or drink from their cup, to reduce contact with saliva
- Wash hands every time after handling a child’s facial tissue to wash off nasal secretions and saliva
- Wash hands every time after changing a child’s diaper to minimize contact with urine
No scientific studies have been done to prove that these precautions reduce the transmission of CMV in pregnancy. However, following them as closely as possible may be of help, and these precautions are recommended by the Centers for Disease Control and Prevention.
References:
CMV, clinical overview and congenital CMV infection. Centers for Disease Control and Prevention.
www.cdc.gov. Page last updated June 17, 2016
Cytomegalovirus, Parvovirus B19, Varicella Zoster, and Toxoplasmosis in Pregnancy. The American College of Obstetricians and Gynecologists. Practice Bulletin Number 151, June 2015.
