CMV, or Cytomegalovirus, is a common virus that can infect people of all ages. Once CMV is in a person’s body, it stays there for life. Most healthy adults and children who become infected will have no signs or symptoms and no long term effects from CMV. It can however pose serious risks to unborn babies if a pregnant woman catches it for the first time. Congenital CMV is when a baby has been infected before birth. It is one of the leading causes of hearing loss in children and one of the main causes of childhood disability.
This section gives some basic information about what CMV is, who is at risk and the difference between CMV and congenital CMV.
Who is at risk of CMV?
Contracting CMV infection during pregnancy poses a risk to the developing baby, as some of these babies are born with permanent health problems. Others at risk include people with low immune systems, for example, people on chemotherapy, or who have had a transplant or who are HIV-positive.
Is congenital CMV a rare condition?
CMV is the most common infection passed from mother to unborn baby.
The majority of babies born with congenital CMV will not have any symptoms at birth and will not suffer any long term problems. However, two or three babies are affected by the CMV virus every day in the UK – almost 1000 babies every year. Congenital CMV is more common than Down's Syndrome and causes more birth defects and childhood deaths than Toxoplasmosis (from cat poo) or Listeriosis (from soft cheese).
What is the difference between CMV & congenital CMV?
Anyone can become infected with CMV. However, most healthy adults and children coming into contact with the virus will have few, if any, symptoms or long-term health problems. Congenital CMV is when CMV infection is transferred from the mother to the unborn baby during pregnancy. Some babies infected in this way will be born with birth defects.
The main ways of catching CMV are:
- Person-to-person contact - CMV is spread from one person to another by close and prolonged contact with bodily fluids such as urine, saliva, blood, faeces, tears, breast milk, semen and cervical secretions. You can catch CMV by kissing, sexual intercourse, sharing eating and drinking utensils, and sharing mouthed toys. You cannot catch CMV by merely being in the same room with someone who is infected.
- Mother to unborn baby - CMV can be transmitted to the developing baby across the placenta, causing congenital CMV.
- Mother to newborn baby - CMV can be transmitted to newborns through the mother’s breast milk or the process of giving birth. It is rare for full-term babies who catch CMV in this way to have problems. However, premature babies or very low birth weight babies can be affected.
- Transplants - CMV may be spread to those receiving organ and bone marrow transplants. The virus can be a particular risk to these patients as their immune system is compromised or weakened.
- Transfusions - Patients who receive a blood transfusion from a donor with CMV infection may acquire CMV themselves. However, donor blood is routinely treated in the UK to reduce these risks and CMV negative blood is recommended for some at-risk groups. People who have a normal immune system are unlikely to have health problems as a result of CMV infection.
What happens in the body during a CMV infection?
When CMV causes an infection for the first time it is called a primary infection. Just as with all infections, the body begins to fight CMV by producing antibodies (protective proteins) and immune cells. While there is an active infection in the body, CMV will be excreted or shed in bodily fluids. However, after infection the virus remains in the body in an inactive state, usually for life. CMV antibodies will be present for life as well.
There are many different strains of CMV. Even if a woman has antibodies against one strain of CMV, she can still get re-infected with a different strain. The body will fight the virus and produce new antibodies just as with a primary infection.
It is possible for any strain of CMV to reactivate or act like a new infection. This type of infection is a recurrent infection and may occur at any time, but especially when the immune system becomes altered or weakened. When reactivation occurs, CMV antibody levels may increase and active CMV will be present in bodily fluids (viral shedding).
Are some people immune to CMV?
If you have had CMV before then you will be immune to that strain of the virus. However, there are lots of different strains of CMV and you will not have natural protection against all of these.