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What is Cytomegalovirus (CMV)?
Cytomegalovirus, commonly abbreviated as CMV, is a virus responsible for a fairly common infection that can affect people of all ages.
In the vast majority of cases, CMV infection causes no symptoms whatsoever, meaning it is a “silent” infection. However, it can lead to serious complications for a developing fetus if contracted during pregnancy, and it can also pose significant risks for patients with a weakened or compromised immune system.
Cytomegalovirus belongs to the herpesvirus family, a group of viruses that also includes those responsible for:
- herpes simplex infections,
- chickenpox (and shingles),
- infectious mononucleosis (caused by the Epstein-Barr virus).
Just like these related infections, once CMV enters the body, it remains there permanently, kept in a dormant, or “latent”, state by the body’s immune system for the rest of a person’s life.
Diagnosis is made through blood tests capable of detecting the presence of IgM and IgG antibodies in the bloodstream, which allow doctors to determine whether:
- an infection is currently active,
- or whether, on the other hand, the patient has already developed the necessary immune defenses following a previous infection.
There is currently no specific antiviral cure that eliminates CMV from the body entirely, and in the majority of patients, no treatment is actually necessary at all, since the immune system manages the infection effectively on its own.
Transmission
Anyone can contract a cytomegalovirus infection, but in most infected adults and children, any symptoms that do occur tend to be mild. The groups of people at greatest risk for serious complications include:
- unborn babies (fetuses), who become infected while their mother is pregnant,
- individuals with a weakened immune system (immunodeficiency).
It is possible to reduce the risk of CMV infection by paying close attention to personal hygiene, such as washing your hands frequently and thoroughly.
Transmission of CMV can occur through:
- direct personal contact, such as kissing, sexual contact, or contact with infected saliva or urine followed by touching the eyes or the inside of the nose,
- breastfeeding by a mother who is infected with the virus,
- transmission from an infected mother to her baby during pregnancy,
- blood transfusions and organ transplants.
When CMV is actively replicating in the body, the virus can be detected in various bodily secretions and fluids, including:
- urine,
- saliva,
- breast milk,
- blood,
- tears,
- semen,
- and vaginal secretions.
A person can become infected through contact with an infected bodily fluid. However, people who were infected with CMV in the past and have since recovered are generally unable to transmit the virus to others under normal circumstances. This means that the risk of catching CMV through brief, casual contact is essentially negligible for the general population.
Contact with the saliva or urine of young children is, however, one of the leading causes of CMV infection among pregnant women, since young children shed the virus much more frequently and for much longer periods than older children or adults.
Anyone who is pregnant, or who is planning to become pregnant, should follow simple hygiene practices, such as frequent handwashing, to help avoid CMV infection. Because young children are considerably more likely to shed CMV in their urine or saliva compared to older children or adults, pregnant women who have young children at home, or who work closely with young children (for example, in childcare settings), should be especially careful.
Symptoms
Most healthy children and adults who become infected with cytomegalovirus experience no symptoms at all, meaning the infection can pass completely unnoticed. Some patients, however, may develop a mild, generally flu-like illness characterized by:
- fever,
- sore throat,
- fatigue,
- swollen lymph nodes.
Because these symptoms closely resemble those of many other common illnesses, most people who are infected with CMV never realize they have contracted the virus.
Congenital and Perinatal Infection
Many babies born with congenital CMV, meaning they were infected with the virus before birth, show no symptoms and have no disabilities at all. In babies who do experience symptoms or complications, these can be either temporary or permanent.
A newborn with congenital CMV infection may:
- show signs of intrauterine growth restriction, resulting in a lower birth weight than expected,
- be born prematurely.
Examples of symptoms or disabilities associated with congenital CMV include:
Temporary symptoms:
- enlargement of the liver (hepatomegaly) along with liver inflammation (hepatitis),
- enlargement of the spleen,
- jaundice (a yellowish discoloration of the skin and eyes),
- small red or purple spots on the skin (petechiae),
- pneumonia,
- seizures.
Permanent problems or disabilities:
- hearing loss,
- vision loss,
- intellectual disability,
- microcephaly (an abnormally small head size),
- lack of coordination,
- seizures,
- and, in severe cases, death.
Babies born with congenital cytomegalovirus infection face a higher risk of developing permanent disabilities and of experiencing worsening of the symptoms present at birth. Some babies who appear perfectly healthy at birth may later develop hearing or vision problems related to CMV only months or even years afterward. For this reason, if you know that your child was infected with cytomegalovirus before birth, regular follow-up hearing and vision screenings are essential throughout early childhood.
It is important to keep in mind that the majority of babies born with congenital cytomegalovirus infection, however, show no symptoms at all and are otherwise perfectly healthy.
Pregnancy
The risk of a baby developing congenital cytomegalovirus infection is highest when the mother is infected with CMV for the very first time during pregnancy. This situation is referred to as primary cytomegalovirus infection.
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Primary infection occurs in an estimated 1 to 4 percent of pregnant women who are seronegative, meaning they have no prior antibodies against cytomegalovirus, and the fetus becomes infected in approximately one third of these pregnancies.
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In women who were already infected with CMV before becoming pregnant (meaning they are seropositive for cytomegalovirus), reactivation of the virus or reinfection with a different strain results in transmission to the fetus in less than 1 percent of cases.
Among babies born with congenital CMV infection, approximately 1 in 10 shows symptoms already at the time of birth. Among the remaining nine, only a variable percentage, estimated at between 10 and 15 percent, will go on to develop symptoms in the months or years that follow.
Nearly all women who have had a child with congenital cytomegalovirus infection are protected against future infections, since they have developed lasting immunity to the virus. A small number of cases have been documented in which a mother had more than one child affected by congenital CMV, but this remains an extremely rare occurrence.
It is worth noting that, following current guidelines on physiological pregnancy, screening for cytomegalovirus infection is now offered to all pregnant women. This recommendation reflects the availability of effective preventive drug protocols capable of reducing the risk of transmission to the fetus:
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Screening blood tests are offered to all pregnant women whose CMV immune status is unknown or who test negative (meaning both IgG and IgM antibodies are negative):
- at the first prenatal visit, and in any case within the first trimester,
- and repeated every 4 to 6 weeks if the first test is negative (both IgG and IgM negative), continuing up to 24 weeks of pregnancy.
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Testing should also be offered whenever an obstetric ultrasound reveals findings suggestive of fetal infection, or when the mother experiences symptoms suggestive of CMV infection.
It is worth noting that recommendations regarding universal CMV screening in pregnancy vary somewhat between countries. In the United States, for example, major professional organizations such as the American College of Obstetricians and Gynecologists (ACOG) have historically not recommended universal screening for all pregnant women, due in part to ongoing debate about testing accuracy and the overall balance of benefits and risks. Practices continue to evolve as new evidence and treatment protocols become available, so pregnant women should discuss the most current, locally appropriate recommendations with their own healthcare provider.
Diagnosis and Monitoring
The diagnosis of cytomegalovirus infection relies primarily on detecting specific antibodies in the blood, although the diagnostic process has evolved considerably to include molecular biology techniques and advanced imaging, particularly for protecting the fetus and other vulnerable patients.
Interpreting Blood Test Results
The first step involves testing for IgG and IgM immunoglobulins (antibodies). IgM antibodies are the first to appear following infection and generally indicate a recent or currently active infection. IgG antibodies appear somewhat later and remain present in the blood for life, providing long-term immune memory.
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IgG negative and IgM negative: The individual is susceptible to infection, meaning they have never previously come into contact with the virus.
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IgG positive and IgM negative: This indicates a past infection. The individual is generally protected, although reactivation of the virus remains possible (this is generally considered less risky for the fetus than a new, primary infection).
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IgG negative and IgM positive: This pattern suggests a very recent infection, likely in its earliest stage.
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IgG positive and IgM positive: This indicates either an active infection or one that occurred relatively recently.
When both IgG and IgM are found to be positive at the same time during pregnancy, it becomes essential to perform an IgG avidity test. High avidity indicates that the infection occurred at least 3 to 4 months before the blood sample was taken, which is generally reassuring for the health of the fetus if conception occurred after this window. Low avidity, on the other hand, suggests a recent primary infection, which requires close monitoring throughout the remainder of the pregnancy.
Prenatal Diagnosis and Imaging
If a primary maternal infection during pregnancy is confirmed, the next step is to determine whether the virus has actually crossed the placenta and infected the fetus. The preferred diagnostic technique for this purpose is amniocentesis, which involves testing the amniotic fluid for viral DNA using a technique called PCR (polymerase chain reaction). For this test to be reliable, it must be performed after the 20th to 21st week of pregnancy, and at least 6 to 8 weeks after the estimated date of maternal infection.
Ongoing monitoring typically continues with a detailed Level II (targeted) ultrasound and, in select cases, fetal MRI (magnetic resonance imaging), usually performed after the 28th week of pregnancy. These imaging studies are aimed at detecting early signs of brain abnormalities or damage to internal organs that may not be visible on standard ultrasound alone.
Diagnosis in the Newborn
To confirm a diagnosis of congenital CMV infection, the virus must be detected in the newborn’s saliva or urine within the first two to three weeks of life. If testing is performed after this window, a positive result may instead indicate an infection acquired during delivery or through breastfeeding, which generally does not carry the same risks for neurological development as a true congenital infection acquired before birth.
Treatment and Clinical Management
The treatment approach for cytomegalovirus infection is highly individualized, depending on the patient’s specific clinical situation. The main treatment goals are to prevent transmission from mother to fetus (known as vertical transmission), to reduce the risk of long-term neurological complications in affected newborns, and to control viral replication in immunocompromised patients.
Treatment During Pregnancy
The medical management of CMV infection during pregnancy has advanced considerably in recent years. When a primary maternal infection is confirmed during the first trimester or early in the second trimester, current clinical protocols in several countries, involve the use of high-dose valacyclovir. This antiviral medication has demonstrated solid effectiveness both in significantly reducing the risk of transmitting the virus to the fetus (referred to as primary prevention) and in improving clinical outcomes when transmission has already occurred (referred to as secondary prevention).
Treatment protocols and drug approvals for CMV in pregnancy can vary between countries. Pregnant women diagnosed with a primary CMV infection should discuss the most appropriate, locally available treatment options with their obstetrician or a maternal-fetal medicine specialist.
Treatment of the Newborn
Newborns diagnosed with symptomatic congenital cytomegalovirus infection, particularly those with evidence of central nervous system involvement or hearing loss, are typically treated with specific antiviral medications, such as valganciclovir (given orally) or ganciclovir (given intravenously). Current scientific consensus recommends a prolonged course of treatment, usually lasting six months, which has been shown to be effective in helping prevent the worsening of hearing loss and in supporting better long-term cognitive development.
Immunocompromised Patients
In transplant recipients or patients with severe immunodeficiency, CMV infection can become life-threatening if not properly managed. In addition to the traditional antiviral medications ganciclovir and foscarnet, newer treatment options are now available, including maribavir, which is specifically indicated for infections that have become resistant to conventional therapies. The choice of medication depends on the patient’s kidney function and their ability to tolerate potential effects on blood cell counts, both of which must be carefully monitored throughout treatment.
Lifestyle and Ongoing Support
For the majority of otherwise healthy individuals who contract the virus, no specific medical treatment is necessary. Rest and adequate hydration are generally sufficient to manage the mild, flu-like symptoms that may occur. For children with lasting effects from congenital infection, ongoing care and support typically includes:
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Regular hearing and vision monitoring throughout the first several years of life, given the possibility of delayed-onset hearing or vision loss.
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Early intervention services, such as speech therapy or physical therapy, when needed to support development.
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Appropriate nutritional support to help promote healthy growth, particularly in children who experienced growth restriction before birth.
Families of children affected by congenital CMV often benefit greatly from coordinated, multidisciplinary care involving pediatricians, audiologists, ophthalmologists, and developmental specialists, working together to identify and address any emerging needs as early as possible.
Prevention
Unfortunately, there is currently no vaccine available to prevent cytomegalovirus infection, although research into potential CMV vaccines is ongoing. In the meantime, expectant mothers can take several simple, practical precautions to reduce their risk of contracting this virus, and other infections that could pose a risk to their baby. If you are pregnant, it is recommended that you:
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Wash your hands frequently with soap and water for 15 to 20 seconds, especially after changing a diaper or coming into contact with a young child’s saliva or nasal secretions.
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Limit contact with the saliva and nasal secretions of young children by taking simple precautions, such as using soap and water or a disinfectant to clean surfaces contaminated with these secretions, avoiding sharing food, drinks, or utensils with young children, and avoiding kissing young children on the mouth.
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Avoid allowing any object that may have been in a child’s mouth, including pacifiers, as well as a child’s hands or feet, to come into contact with your own mouth or oral mucosa, since up to around age three, the virus is present primarily in a young child’s saliva and urine.
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If you work in a childcare setting, try to minimize close contact with children under the age of two and a half, particularly if you have never been infected with CMV before, or if you are unsure of your CMV immune status.
Beyond these specific measures related to young children, general good hygiene practices, such as not sharing drinking glasses, eating utensils, or toothbrushes with anyone, and practicing safe sex, can also help reduce the overall risk of CMV transmission for people of all ages, not only pregnant women.
Frequently Asked Questions
What is cytomegalovirus?
Cytomegalovirus (CMV) is a virus capable of causing an infection that goes essentially unnoticed in the vast majority of patients. However, it can pose serious health risks for individuals with a weakened immune system, as well as for babies whose mothers become infected during pregnancy.
How is CMV treated?
Unfortunately, there is no specific cure that eliminates the virus from the body entirely. In experimental settings, infusions of immunoglobulins have been used to help support the immune system’s ability to fight the infection, and specific antiviral medications (such as valacyclovir, ganciclovir, and valganciclovir) are used in particular clinical situations, such as pregnancy, congenital infection, or immunocompromised patients, as described above.
How should I interpret my CMV test results?
There are four possible combinations of results:
- IgG and IgM both negative: the infection has never been contracted.
- IgG positive and IgM negative: the infection was contracted in the past, but is not currently active.
- IgG negative and IgM positive: the infection is recent and currently active.
- IgG and IgM both positive: the infection is currently active or occurred relatively recently.
How long do IgM antibodies remain positive?
The length of time that IgM antibodies remain detectable in the blood, indicating an active infection, can vary considerably. Typically, IgM antibodies appear within one to two weeks after initial infection and remain measurable for approximately four months in about three out of every four patients. In the remaining cases, IgM antibodies may persist for up to a year. For this reason, doctors often rely on the IgG avidity test to more accurately estimate when the infection actually occurred, rather than relying on IgM results alone.
How is CMV spread?
CMV spreads primarily through close contact with a person who has an actively replicating infection. The virus is present in various bodily fluids, including saliva, blood, and urine. A person is considered to have an “active” infection:
- when they are infected with the virus for the very first time,
- when a previous, dormant infection reactivates,
- or when they become infected with a different strain of the virus than one they were previously exposed to.
Unfortunately, pregnant women with an active CMV infection can transmit the virus to the developing fetus, which is why understanding transmission routes and practicing preventive hygiene measures is particularly important during pregnancy.
Can CMV be completely cured?
No, there is currently no treatment that completely eliminates CMV from the body. Like other herpesviruses, once a person is infected, the virus remains in the body for life in a dormant state, kept in check by the immune system. Treatment, when necessary, focuses on controlling active viral replication and preventing complications, rather than achieving a complete cure.
Is CMV the same as the flu or a cold?
No, although the mild symptoms of CMV infection, such as fever, sore throat, and fatigue, can resemble those of a common cold or mild flu. CMV is a distinct virus belonging to the herpesvirus family, and unlike the flu, it establishes a lifelong, dormant infection in the body once contracted.
Should everyone be tested for CMV during pregnancy?
Recommendations vary by country and healthcare system. In some countries, universal screening is offered to all pregnant women as part of official prenatal care guidelines. In others, such as the United States, universal screening is not currently recommended by all professional guidelines, and testing decisions are often made based on individual risk factors or specific clinical findings. Pregnant women should discuss the most appropriate approach with their healthcare provider, based on current local guidelines.
Sources and Bibliography
- Centers for Disease Control and Prevention (CDC). “Cytomegalovirus (CMV) and Congenital CMV Infection”. Available at: https://www.cdc.gov/cytomegalovirus/about/index.html
- Istituto Superiore di Sanità (Epicentro). “Citomegalovirus”. Available at: https://www.epicentro.iss.it/problemi/citomegalovirus/citomegalovirus.asp
- Italian National Guideline System (SNLG). “Linee Guida Gravidanza Fisiologica” (Guidelines on Physiological Pregnancy).
- American College of Obstetricians and Gynecologists (ACOG). “Cytomegalovirus, Parvovirus B19, Varicella Zoster, and Toxoplasmosis in Pregnancy”. Available at: https://www.acog.org
- National Institutes of Health (NIH), National Institute on Deafness and Other Communication Disorders (NIDCD). “Cytomegalovirus (CMV) and Hearing Loss”. Available at: https://www.nidcd.nih.gov
- Mayo Clinic. “Cytomegalovirus (CMV) Infection”. Available at: https://www.mayoclinic.org
- MedlinePlus, U.S. National Library of Medicine. “Cytomegalovirus (CMV) Infection”. Available at: https://medlineplus.gov
