Five things to know about cytomegalovirus (CMV)
Even though cytomegalovirus, or CMV, is the most common infectious disease in the United States that causes disability in children, most people have never heard of it. It’s a member of the herpes family of viruses.
One in three children is infected with CMV by the time they’re 5. Half of adults are infected by age 40, according to the Centers for Disease Control and Prevention. Once a person has the virus, they will carry it for life.
It’s not well known because most people experience only mild symptoms like sore throat, fever, or muscle aches when they’re first infected. In more serious cases, CMV can lead to mononucleosis (mono) or hepatitis, which is inflammation of the liver.
The biggest risk comes when a person gets infected during pregnancy. Pregnant people can pass the virus to their babies both before and after birth. Babies are particularly vulnerable to CMV, because their immune system isn’t fully developed yet.
“It's an illness of no real importance – unless you're pregnant. Then it can be absolutely devastating,” said Mark Schleiss, MD, a pediatric infectious diseases provider with M Health Fairview and a professor at the University of Minnesota Medical School.
Schleiss shares five things to know about CMV.
CMV infection during pregnancy can cause birth defects
Maternal CMV infections acquired during the first trimester of pregnancy are more likely to cause complications in the newborn than infections late in pregnancy. The most common issue is hearing loss. About 20% of babies born with CMV will develop hearing loss. Up to half of infants who eventually have CMV-associated hearing loss will pass their initial newborn hearing screen.
Babies born with CMV are often small for gestational age, or premature. They might also have liver, spleen, lung, and growth problems that get better with time. Brain injuries, though less common, do not improve with age.
Signs of CMV include:
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A small head size
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Smaller body than expected for age
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Skin rash
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Jaundice, which is yellowing of skin and whites of eyes
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Enlarged liver and spleen
CMV is passed through person-to-person contact
CMV spreads easily through bodily fluids, like saliva, urine, blood, tears, and semen. Babies can become infected after birth through breast milk. CMV is also spread through saliva in settings like daycare centers. Infected children can also spread it to their caregivers through kisses, shared utensils, or diaper changes.
Unless a person is pregnant or has a compromised immune system, getting infected with CMV is generally uneventful.
There’s no way of knowing when CMV will be problematic
About 1 in 200 babies is born with congenital CMV, according to the CDC. Of those, about 1 in 5 will have birth defects or long-term health problems.
“One of the interesting features of CMV is that it's not uniformly devastating to every pregnant person who gets it,” Schleiss said. “There’s no way of knowing who will become infected and which of them will have affected children.”
During pregnancy, the body’s immune defenses are lowered, increasing the chances of getting an infection like CMV. Even people who were already infected and carry the virus can get re-infected. It’s similar to how people can get infected with a new strain of COVID-19, Schleiss said.
Minnesota tests for CMV at birth
In 2023, Minnesota became the first state to test newborn babies for CMV, thanks in part to the advocacy of doctors like Schleiss and families who have experienced the disease. Screening is done as part of a heel prick blood test. If a child has congenital CMV, healthcare providers can monitor for hearing loss and neurological development to provide therapies early. In some cases, infants might benefit from antiviral medication that can lessen damage to brain and ear development.
There’s a vaccine in the works
Rather than treating the effects of CMV, Schleiss is passionate about preventing pregnant people from getting infected in the first place. “The best way to do that is a vaccine,” Schleiss said.
Schleiss and his research team are looking for volunteers to test a CMV vaccination.
“Vaccines exist to protect communities and protect the people you love,” Schleiss said. “There's value in talking about a vaccine that presumably would be given to everybody to protect 15% of the population."
He cites rubella as being a similar virus that is typically asymptomatic unless a person is infected during pregnancy. Then it can cause low birth weight, hearing loss, and liver or brain damage in the newborn. To prevent rubella infections in pregnant people, we started vaccinating children when they’re toddlers. This provides “herd” immunity that protects against transmission of infection in the community. While congenital rubella is still a global issue, it’s rare in the United States and the vaccine is considered to be a major success for public health.
