Causes of cytomegalovirus (CMV)


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

CMV is a common virus, related to the viruses that cause chickenpox and glandular fever, which spread in similar ways. 

How CMV is spread

CMV is primarily spread through bodily fluids, including:

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

You can get the CMV virus by touching surfaces infected with contaminated 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. However, by the time a child is old enough to attend, their immune system (the body’s natural defence against infection and illness) should be strong enough to deal with an infection.

If you experience any symptoms of a CMV infection, they should pass quickly and the virus will then remain inactive in your body’s cells for the rest of your life.

Recurring CMV

CMV can become a problem if your immune system becomes severely weakened, leading to the virus "waking up" and re-infecting your body’s organs.

Your immune system may become weakened if you:

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 baby if it is born prematurely.

Congenital CMV

Congenital CMV is when an unborn baby develops a CMV infection from its mother.

Most cases of congenital CMV develop when a pregnant woman is infected by the CMV virus for the first time during, or shortly before, pregnancy. In around 4 out of 10 cases, the baby will be infected as well.

In some cases, a previously inactive CMV infection can recur during pregnancy if the mother has a weakened immune system. The mother could also be re-infected with another strain of the CMV virus, which can also be passed to her unborn baby.

In the majority of cases, the virus does not harm the baby. However, if a large amount of the virus spreads to the baby, it can interfere with the baby’s normal development, resulting in the associated disabilities and symptoms of congenital CMV.