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.
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.
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.
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.
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.
Cells infected with cytomegalovirus (CMV)
Symptoms of cytomegalovirus (CMV)
Most cases of CMV don't cause any symptoms and you may not even realise you're infected.
If you do experience symptoms, they'll be similar to flu symptoms or symptoms of glandular fever. They can include:
a high temperature of 38C (100.4F) or above
muscle and joint pain
loss of appetite
hepatitis (inflammation of the liver)
These symptoms will usually last for a couple of weeks.
If CMV recurs in someone who's otherwise healthy, including during pregnancy, it will cause few, if any, symptoms.
Weakened immune system
Active CMV infection in someone with a weakened immune system can cause a wide range of symptoms, including:
a high temperature
shortness of breath
visual problems – such as blind spots, blurring and floaters
pneumonia (inflammation of the tissue in the lungs)
retinitis – inflammation of the retina (the light-sensitive layer of tissue at the back of the eye)
hepatitis – inflammation of the liver
These symptoms occur because the virus can quickly spread throughout the body, damaging one or more organs, particularly the digestive system, lungs and eyes.
Contact your GP or treatment team immediately if you have one or more of the above symptoms and your immune system is weakened by HIV or organ transplantation.
Around 13% of babies born with congenital CMV will have symptoms at birth. A similar number of babies who don't have symptoms at birth will develop problems at a later stage.
Symptoms at birth
Symptoms of congenital CMV at birth can include:
jaundice (yellowing of the skin and whites of the eyes)
pneumonia (lung infection)
a rash consisting of small, purplish spots
an enlarged liver and spleen
low birth weight
Some of these symptoms can be treated, but some babies will develop long-term conditions as a result of the infection.
A small proportion of babies with congenital CMV (including those with no symptoms at birth) will develop one or more physical or mental problems at a later stage. These can include:
hearing loss (see below)
visual impairment or blindness
dyspraxia (lack of physical co-ordination)
epilepsy (a condition that affects the brain and causes repeated seizures)
CMV infection is responsible for around 25% of cases of hearing loss during childhood.
Hearing loss caused by congenital CMV may develop during the first few years of life. This usually gets worse over time. It can also be permanent and range from mild to total.
The hearing problems can affect either one or both ears. Children with hearing loss in both ears are also likely to experience difficulties with speech and communication as they get older.
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:
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.
CMV can be a problem in 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 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.
Treating cytomegalovirus (CMV)
Cytomegalovirus (CMV) infections only usually require treatment if there's a risk of serious complications.
Most CMV infections don't cause any symptoms and don't need to be treated.
If you have symptoms after being infected with CMV for the first time, over-the-counter painkillers such as paracetamol or ibuprofen can help relieve the symptoms of pain and fever (however, children younger than 16 shouldn't take aspirin).
Drinking plenty of water will help relieve the symptoms of a fever and sore throat, and will prevent dehydration.
Antiviral medicine may be needed to treat congenital CMV or active CMV in someone with a weakened immune system.
This medicine can't cure the infection, but it can slow its progress and limit the possibility of serious damage.
Ganciclovir (Cymevene) is an antiviral medicine often used to treat CMV. An oral form called valganciclovir (Valcyte) is often used. However, it can't be prescribed during pregnancy.
Ganciclovir can cause several side effects, the main one being bone marrow suppression. Bone marrow is the spongy material at the centre of some bones. It produces the stem cells that produce blood cells and platelets.
Suppressed bone marrow can lead to a low white blood cell count, which increases the risk of serious bacterial infection. Low levels of platelets can cause increased bleeding, and a lack of red blood cells can cause anaemia, which may lead to severe tiredness.
Other possible antiviral medicines include foscarnet (Foscavir) and cidofovir (Vistide).
A course of antiviral medicine will usually be prescribed for a minimum of 14 days.
A baby born with congenital CMV may need to stay in hospital until their normal organ function returns. They will also need to stay in hospital if they're being treated with the antiviral medicine ganciclovir, at least when treatment is first started.
Once the baby is well enough to go home, the course of treatment can be completed with valganciclovir. In many cases, valganciclovir can be given from the start of the treatment.
Your baby should also have regular hearing and eye tests to check for any problems.
Adults with a weakened immune system and organ damage from CMV may need to be admitted to hospital for treatment.
Preventing cytomegalovirus (CMV)
It's not always possible to prevent a cytomegalovirus (CMV) infection, but there are steps you can take to reduce the risk.
Most people don't worry about preventing CMV, because it doesn't often cause symptoms. However, you should be careful if you're at increased risk of developing more serious problems or if you're planning a pregnancy.
Newborn babies, pregnant women, people receiving an organ transplant and people with a weakened immune system have an increased risk of developing serious problems.
A person donating an organ will be screened for CMV before or at the time of the organ transplant.
Maintaining high levels of hygiene is a simple measure that may help prevent a CMV infection spreading. For example, always wash your hands with soap and warm water:
before preparing, serving or eating food
after going to the toilet
after changing a baby’s nappy
after coming into contact with bodily fluids, such as semen or urine
You should clean any surfaces that have come into contact with bodily fluids, and wear disposable gloves while doing this.
CMV infections are common in young children. If you're pregnant, you can reduce your risk of becoming infected by taking some simple measures, such as:
regularly washing your hands with soap and hot water, particularly if you've been changing nappies, or you work in a nursery or day care centre
not kissing young children on the face; it's better to kiss them on the head or give them a hug
not sharing food or eating utensils with young children, or drinking from the same glass as them
These precautions are particularly important if your job brings you into close contact with young children. If it does, you can have a blood test to find out whether you've previously been infected with CMV.
CMV is particularly dangerous to the baby if the pregnant mother hasn't had a previous CMV infection. However, all pregnant women should follow the hygiene precautions above to reduce their risk of infection, even if they've had CMV before, because they could be infected with a different strain of the virus.
CMV used to be one of the main causes of illness and death during the first six months after having an organ transplant. However, antiviral medicines have proved very effective in preventing CMV infections in people who've received transplants.
Therefore, it's likely that you'll be given antiviral medicines to help prevent a CMV infection developing into a problem if you're having an organ transplant.
Weakened immune system
Your immune system may be weakened if you have HIV, or you're taking medication to prevent a transplanted organ being rejected. The immune system is the body's natural defence against illness and infection. If it's weakened, you'll be more vulnerable to infections, including CMV.
As well as maintaining a high level of hygiene, you can help prevent infections developing by:
having daily showers or baths, and washing your clothes, towels and bed linen regularly
avoiding contact with people who have serious infections, such as chickenpox or flu
taking extra care not to cut or graze your skin (if you do, clean the area thoroughly with warm water, dry it and cover it with a sterile dressing)
eating a healthy, balanced diet that includes plenty of fresh fruit and vegetables
resting when you need to
asking your friends and relatives to make sure their flu vaccines, MMR vaccines and chickenpox vaccines are up-to-date before they visit you
Contact your GP if you have a weakened immune system and you think you may have an infection – for example, if you have a high temperature of 38C (100.4F) or above.
Research is currently underway to find vaccines for CMV.
One possible vaccine is aimed at young women. The theory is that vaccinating women before they become pregnant could reduce the risk of congenital CMV.
Another possible vaccine is aimed at toddlers. By reducing their chance of getting active CMV, their mothers may be protected from CMV during pregnancy.
A third possible vaccine is aimed at people having organ transplants. The aim is to prevent the donated organ causing a new CMV infection or reactivating an existing CMV infection in the person receiving the transplant.
However, because of the stringent safety checks that all new medicines and vaccinations have to go through, it's likely to be several years before routine vaccinations against CMV are available.