Cytomegalovirus, usually called CMV, is an extremely common virus that most people carry without ever knowing it. It belongs to the herpesvirus family (officially named human herpesvirus 5) and, like its relatives, it stays in your body for life once you’re infected. For the vast majority of healthy people, CMV causes no symptoms at all. It becomes a serious concern primarily for people with weakened immune systems and for babies infected before birth.
How Common CMV Really Is
CMV is one of the most widespread human infections on the planet. Most adults have been exposed by middle age. Global prevalence varies by region and socioeconomic factors, but in many populations the majority of adults carry the virus. Because it rarely causes noticeable illness in healthy people, most carriers have no idea they’re infected.
How CMV Spreads
CMV travels through body fluids: saliva, urine, blood, tears, semen, and breast milk. The most common routes of transmission include direct contact with saliva or urine (especially from babies and young children, who shed the virus in large amounts), sexual contact, breastfeeding, organ transplants, blood transfusions, and passage from a pregnant person to their baby during pregnancy.
Young children in daycare settings are particularly efficient spreaders. A toddler with CMV can shed the virus in saliva and urine for months or even years, which is why parents and childcare workers face higher exposure.
Symptoms in Healthy Adults
Most healthy people who catch CMV never develop symptoms. When symptoms do appear, they typically resemble a mild case of mono: fatigue, fever, swollen lymph nodes, and body aches. This resolves on its own without treatment and rarely causes lasting problems. Many people mistake it for a lingering cold or flu and never get tested.
Why CMV Is Dangerous for Some People
CMV becomes a different disease entirely in people whose immune systems are compromised, including organ transplant recipients on immunosuppressive drugs, people with advanced HIV, and those undergoing chemotherapy. In these groups, CMV can invade specific organs and cause serious, sometimes life-threatening illness.
The virus can attack the digestive tract, causing painful swallowing, diarrhea, abdominal pain, and weight loss. It can infect the lungs, leading to cough, shortness of breath, and dangerously low oxygen levels. CMV retinitis, an infection of the retina, causes painless vision loss that can become permanent without treatment. In rare cases, the virus reaches the brain, causing confusion, seizures, and altered consciousness.
Congenital CMV: The Risk During Pregnancy
Congenital CMV, meaning infection passed from mother to baby during pregnancy, is the leading infectious cause of birth defects in many countries. About 1 in 5 babies born with congenital CMV will develop birth defects or long-term health problems.
Some infected newborns show signs at birth: a rash, jaundice, an abnormally small head, low birth weight, an enlarged liver and spleen, seizures, or damage to the retina. Others appear healthy at birth but develop problems later, particularly hearing loss, which can emerge months or even years after delivery. Other long-term effects include developmental delays, vision loss, coordination problems, and seizures.
The risk is highest when a pregnant person catches CMV for the first time during pregnancy, rather than experiencing a reactivation of an old infection. This is why prevention matters so much for women who haven’t been previously exposed.
How CMV Hides in Your Body
Once you’re infected, CMV doesn’t leave. The virus embeds itself in blood-forming stem cells in the bone marrow and goes dormant, a state called latency. Your immune system keeps it in check, but the virus is never fully eliminated. It essentially turns off most of its genes and waits.
Reactivation can happen when the immune system is weakened or distracted. Triggers include inflammation, serious infection, physical injury, and the immunosuppressive drugs used after organ transplantation. Even normal biological processes like cellular stress and aging can nudge the virus back into activity. In a healthy person, reactivation is usually controlled quickly and goes unnoticed. In someone with a compromised immune system, it can spiral into active disease.
How CMV Is Diagnosed
Doctors use blood tests to determine whether you’ve been infected and, if so, how recently. The key distinction is between two types of antibodies your body produces in response to the virus.
A positive IgG antibody test means you’ve been infected at some point in the past. A positive IgM antibody test suggests a more recent or active infection, but IgM alone isn’t enough for a definitive diagnosis because it can linger for months and occasionally gives false positives. To pin down whether an infection is truly recent, doctors use an IgG avidity test. Low avidity means the infection likely occurred within the last two to four months. High avidity points to an older infection. This timing distinction matters most during pregnancy, where a new infection carries the greatest risk to the baby.
For immunocompromised patients, doctors often rely on PCR testing, which detects the virus’s genetic material directly in the blood. This allows them to catch reactivation early, sometimes before symptoms even appear, and start treatment quickly.
Treatment Options
Healthy adults with CMV generally don’t need treatment. The infection clears on its own, and rest and fluids are typically enough to manage any symptoms.
For immunocompromised patients, antiviral medications are essential. These drugs work by blocking the virus’s ability to replicate. Treatment is typically used for active CMV disease in transplant recipients and for CMV retinitis in people with AIDS. Antivirals are also given preventively to organ transplant recipients who are at high risk for CMV reactivation. Treatment can last weeks to months depending on the severity of the infection and how well the immune system recovers.
For newborns with symptomatic congenital CMV, antiviral treatment started in the first month of life can improve hearing and developmental outcomes, though it doesn’t reverse all damage.
Reducing Your Risk
There is no approved vaccine for CMV yet, though candidates are in clinical development. Prevention currently relies on practical hygiene measures, which are especially important for pregnant women who haven’t been previously infected.
The strategies are straightforward: wash your hands thoroughly after changing diapers or wiping a child’s nose, avoid kissing young children on the mouth or cheeks, and don’t share utensils, cups, food, or washcloths with toddlers. These precautions are backed by strong evidence. In one study, pregnant women who received counseling on these hygiene behaviors had a CMV infection rate of just 1.2%, compared to 7.6% among women who weren’t counseled. That translates to an 86% reduction in risk, a striking result for such simple interventions.