What Is Cytomegalovirus? Symptoms, Infection and Treatment Explained

The U.S. Centers for Disease Control and Prevention (CDC) has advised people to be wary of cytomegalovirus (CMV) during the holiday season.

CMV is a common virus for people of all ages that is usually not harmful, though it is associated with birth defects in babies that are born with it.

Nearly one in three children in the U.S. are already infected with it by the time they are 5 years old, and over half of adults have it by the time they're 40, the CDC states.

Once someone is infected with CMV they have the virus for life. Most people with CMV don't get any symptoms and may not even be aware they have the virus at all. A healthy person's immune system usually keeps the virus from causing illness, the CDC states.

When symptoms do appear, healthy people may experience a fever, sore throat, fatigue, swollen glands or muscle ache, according to the CDC and Mayo Clinic.

However, in people with weakened immune systems, CMV may cause more serious symptoms which can affect the eyes, lungs, liver, esophagus, stomach, and intestines.

In addition, babies born with CMV can experience brain, liver, spleen, lung, and growth problems with a common issue being hearing loss. The CDC states that CMV is the most common infectious cause of birth defects in the U.S. and one out of five babies born with it will have birth defects or other long-term health problems.

CMV is transmitted via bodily fluids such as saliva, urine, blood, tears, semen and breast milk. As such it can be transferred between people through contact with saliva or urine, sexual contact, breastfeeding or through an organ transplant or blood transfusion. It can be diagnosed via a blood, urine, or saliva test.

According to the U.K.'s National Health Service (NHS), CMV is passed on when it's "active," such as when someone gets it for the first time—children often get it in nurseries—or when they are reinfected with a different variant, or when it gets re-activated in the body due to a weakened immune system. Pregnant women can pass an "active" CMV infection onto their unborn baby.

CMV may sometimes cycle between an active and dormant stage, though in healthy people it usually stays dormant, according to the Mayo Clinic.

In a tweet posted on Wednesday the CDC said that people can avoid CMV by not sharing cups or other items that may have saliva on them.

In addition, the Mayo Clinic states people should take care with their hygiene, such as avoiding kissing a child on the lips—"especially important if you're pregnant." Washing hands often and well with soap and water for 15 to 20 seconds is also advised.

More information on prevention can be found on the CDC and Mayo Clinic websites.

Treatments are available for people with CMV, though healthy people do not usually require them.

Babies with CMV at birth, for example, may benefit from antiviral medications like valganciclovir that may improve developmental outcomes, the CDC states—though this can have serious side effects.

Research is ongoing to characterize the impact of CMV on various populations and assess the long-term outcomes in children who are born with it.

Moderna CEO Stéphane Bancel has previously told Newsweek that Moderna has looked into developing a CMV vaccine.

Washing hands
A stock photo shows someone washing their hands. The Mayo Clinic states that careful personal hygiene like washing hands well with soap and water and avoiding contact with saliva may help reduce the risk of spreading CMV. AlexRaths/Getty