Causes of cytomegalovirus (CMV) 

Infection with cytomegalovirus (CMV) is mainly caused by close physical contact.

CMV is a common virus that is related to the viruses that cause chickenpox and glandular fever

How CMV is spread

CMV is primarily spread through bodily fluids, including:

  • saliva
  • semen
  • blood
  • urine
  • vaginal fluids
  • breast milk

You can become infected by touching surfaces that are contaminated with saliva or urine, and then touching the inside of your nose or mouth. CMV can also be spread during kissing or sexual intercourse.

Most CMV infections occur in early childhood. The infection can spread rapidly in places where young children spend time in close contact with each other, such as day care centres and nurseries.

By the time a child is old enough to attend, their immune system should be strong enough to deal with an infection. However, they can take CMV home to their mother, who may be pregnant.

If you experience symptoms of a CMV infection, they should pass quickly. If you're healthy, the virus will lie dormant (inactive) in your body's cells for the rest of your life.

Active CMV

CMV can be a problem for people who have a severely weakened immune system, leading to the virus infecting the body's organs.

Your immune system may become weakened if you:

  • have HIV that's not currently being treated 
  • have been taking oral steroid tablets for more than three months, or other types of high-dose steroids or immunosuppressants
  • are taking medication needed for a transplant 

Active CMV frequently occurs after a person has had an organ transplant or a bone marrow transplant.

CMV and breastfeeding

CMV can be passed from a mother to her child through breast milk. However, the benefits of breastfeeding your baby far outweigh any risk from CMV.

The one exception is if a child is born prematurely. The immune system of premature babies is often not strong enough to deal with a CMV infection. Your treatment team will advise you on the best way to feed your premature baby.

Congenital CMV

Congenital CMV is where a mother passes a CMV infection on to her unborn baby.

Some cases occur when a pregnant woman is infected by CMV for the first time during, or shortly before, pregnancy (a primary infection). In around 3 out of 10 cases, the baby will also be infected.

In some cases, a previously inactive CMV infection can recur during pregnancy. The mother could also be reinfected with another strain of the CMV virus, which can be passed to her unborn baby.

In the majority of cases, the virus doesn't harm the baby. However, in severe cases, it can interfere with the baby’s normal development, resulting in the associated disabilities and symptoms of congenital CMV.


Page last reviewed: 17/11/2014

Next review due: 17/11/2016