CMV Cheat Sheet

CMV = Cytomegalovirus

CMV is a herpes virus that the majority of people have been infected with. Most immunocompetent people do not know when they were infected due to very mild symptoms or a complete lack of symptoms. But most of us would have been infected as children. CMV is not something a healthy adult needs to worry about...unless they get pregnant.

Some facts:

• 50-85% of people have been infected with CMV
• no vaccine for CMV
• most people are asymptomatic
• CMV is spread through bodily fluids
• CMV lays dormant (like all herpes viruses)

CMV infection during pregnancy

Women who have never been infected with CMV are at risk of getting a primary CMV infection during pregnancy. Most pregnant women are asymptomatic and have no idea an infection has occurred. To combat this, pregnant women are tested for CMV-specific antibodies in the blood. If positive, further testing is usually required to determine if it is a primary infection. Unfortunately, mothers who have primary infections of CMV can vertically transmit the virus to the fetus through the placenta. The fetus has a very high chance of getting infected if the mother gets infected during pregnancy. Additionally, the vertical transmission of CMV to the baby can occur during labor or breastfeeding. Although transplacental transmission rates increase with gestational age, the symptoms and disease outcomes decrease as the pregnancy progresses.

Roughly 10-15% of CMV-infected fetuses have abnormalities at birth. But some babies do not have symptoms at birth, but develop symptoms later on during childhood.

Congenital CMV affects the development of the fetal central nervous system. Of the non-genetic causes of sensorineural hearing loss, congenital CMV is the major contributer.

If you are already CMV+ before pregnancy, your chance of a recurrent infection leading to transmission to the baby is only 1-2%. If you go into pregnancy CMV-, your chance of passing CMV to the baby is 40% if you get a primary infection during the pregnancy (but your chance of getting a primary CMV infection during pregnancy is only 1-4%).

TLDR:

CMV is a virus that is not a concern unless you have a weakened immune system or you are pregnant. Most of us have been infected with CMV previously and were asymptomatic. CMV can be passed from mother to fetus during pregnancy and can lead to fetal abnormalities. Infections that occur during the first trimester have the greatest risk of hearing, vision, and brain abnormalities.

Key phrases:

• Asymptomatic means lacking any symptoms
• Immunocompetent means healthy immune system (opposite of immunocompromised)
• Congenital means a condition or trait present at birth
• Vertical transmission means the virus can pass from mother to child through the placenta, during delivery, or after birth through breastmilk
• Primary infection means the first time the patient got infected
• Sensorineural hearing loss (SNHL) is a fancy way of saying hearing loss caused by a defect in the inner ear