Causes of cytomegalovirus

Acquired cytomegalovirus

The cytomegalovirus (CMV) is spread through bodily fluids. These include:

  • saliva,
  • semen,
  • blood,
  • urine,
  • vaginal fluids, and
  • breast milk.

Close physical contact

CMV infection can be spread through close physical contact. For example, when small droplets of infected saliva are transmitted from one person to another when an infected person coughs or sneezes.

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

Most CMV infections occur in early childhood. In places where young children spend a lot of time in close contact with other children, such as daycare centres and nurseries, a rapid spread of a CMV infection can occur.

However, do not avoid sending your child to daycare or nursery because by the time they're old enough to attend, their immune system should be strong enough to deal with an infection.

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

CMV will only 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're taking immunosuppressant medication because you've had an organ transplant,
  • you have HIV,
  • you are receiving chemotherapy,
  • you have been taking steroid tablets (oral steroids) for more than three months.

CMV and breastfeeding

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

The one exception to this is if a child is born prematurely. The immune systems of premature babies are often not strong enough to control a CMV infection. If your baby is born prematurely, your treatment team will be able to advise you about the best option for feeding your baby.

Congenital CMV

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 some cases, a previously dormant CMV infection can recur during pregnancy as a result of the mother having a weakened immune system. If this happens, the CMV virus can then be transmitted from the mother to the unborn baby.

In the majority of cases where CMV is transmitted from a mother to her unborn baby, the virus doesn't cause any damage to the baby. But if a large number of virus cells (high viral load) is spread to the baby, it can interfere with the baby’s normal development, resulting in the symptoms and associated disabilities of congenital CMV.


Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.  
The uterus (also known as the womb) is a hollow, pear-shaped organ in a woman where a baby grows during pregnancy.
Chemotherapy is a treatment of an illness or disease with a chemical substance, e.g. in the treatment of cancer.
Sneezing is an involuntary expulsion of air and bacteria from the nose and mouth.
Stool (also known as faeces) is the solid waste matter that is passed from the body as a bowel movement.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Bone marrow donation
Bone marrow donation is volunteering to give some of the tissue from the inside of your bones, to help someone else who’s bone marrow has been damaged
Last updated: 04 October 2011

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