Cytomegalovirus (CMV) is a common virus that belongs to the herpes family of viruses. 

It's spread through bodily fluids, such as saliva and urine, and can be passed on through close contact with young children, such as when changing nappies.

CMV can also be passed on through kissing, having sex, or receiving an infected organ during an organ transplant.

Read more about the causes of CMV infections.

Most cases of CMV don't cause symptoms. If you do have symptoms, they're often similar to flu or glandular fever, and include a high temperature (fever), sore throat and swollen glands.

Read more about the symptoms of CMV.

Stages of infection

You can get CMV at any age, but many people are first infected during childhood and are unaware they've been infected. 

When you develop a CMV infection for the first time, it's known as primary CMV. It's thought that 50-80% of adults in the UK are infected with CMV.

Once you've been infected, the CMV virus stays in your body for the rest of your life, but in most cases it remains inactive and doesn't cause further problems.

However, CMV can sometimes be reactivated (recur). This usually only occurs in people who have a weakened immune system  for example, due to untreated HIV or taking immunosuppressant medication to prevent transplanted organs being rejected.

It's also possible to become infected again with a different strain of the CMV virus. This is known as reinfection and usually causes similar symptoms to a primary infection.

“Active CMV” is a term that describes someone who's infectious to another person and can be due to primary infection, reinfection or reactivation.

Congenital CMV

If a pregnant woman has an active CMV infection, the virus can be passed to her unborn baby. When it affects a baby in the womb, it's known as congenital CMV.

In the UK, it's estimated that one to two babies in every 200 will be born with congenital CMV. Of these, about 13% will have problems at birth, such as hearing loss and learning difficulties, with a similar number developing problems later on.

Treating a CMV infection

CMV isn't usually diagnosed because it doesn't cause symptoms for most people. If you're at risk of developing complications, a blood test can help determine whether you've ever had CMV or if you've recently caught it for the first time.

Urine and saliva swab tests can be used to find out whether a newborn baby has congenital CMV.

Most CMV infections are mild, don't cause symptoms and don't need to be treated. If you do have symptoms, painkillers can be used to help reduce any pain or fever.

Active CMV in someone with a weakened immune system is usually treated with antiviral medicines, which slow the spread of the virus. Some cases may need to be treated in hospital. Babies with congenital CMV may also need antiviral treatment.

Read more about treating CMV.

Preventing a CMV infection

It's not always possible to prevent the spread of CMV, but you can reduce your risk by practising good hygiene, such as regularly washing your hands with soap and warm water. This is particularly important after changing nappies. You should also try to avoid coming into contact with the saliva of young children.

Research is currently being carried out to find a possible vaccine for CMV. However, it's unlikely that a vaccine will be available for several years.

Read more about preventing CMV.

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