CMV Virus

Dec 09, 2020

Cytomegalovirus (CMV) is a common virus that occurs widely throughout the population but rarely causes symptoms. In the United States, as many as 50-85% of adults have been infected with CMV. Most people are infected as children or as young adults and do not experience any significant symptoms or health problems.

CMV testing involves either a measurement of CMV antibodies, immune proteins produced in response to CMV exposure, or the detection of the virus itself. The virus can be identified during an active infection by culturing CMV or by detecting the virus’s genetic material (DNA) in a fluid or tissue sample.

CMV is found in many body fluids during an active infection, including saliva, urine, blood, breast milk, semen, vaginal secretions, and cerebrospinal fluid. It is easily transmitted to others through close physical contact or by contact with infected objects, such as diapers or toys. After the initial “primary” infection has resolved, CMV becomes dormant or latent, like other members of the herpes family. Cytomegalovirus remains in a person for the rest of the person’s life without causing any symptoms unless the person’s immune system is significantly weakened. If this happens, the virus can reactivate.

CMV can cause notable health problems in three situations:

  • In young adults, primary CMV infection may cause a flu-like or mononucleosis-type illness. This condition, which causes symptoms such as extreme fatigue, fever, chills, body aches and/or headaches, usually resolves within a few weeks. 

  • In infants, primary CMV infection may cause serious physical and developmental problems. This occurs when a woman is infected for the first time (primary infection) during pregnancy and then passes the infection to her developing baby across the placenta. Most newborns (about 90%) who are infected appear healthy at birth but may develop hearing or vision problems, pneumonia, seizures, and/or delayed mental development a few months later. A few babies may be stillborn, while others may have symptoms at birth such as jaundice, anemia, an enlarged spleen or liver, and a small head.

  • In those with weakened immune systems, CMV could cause serious illness and death. This includes those with HIV/AIDS, those who have had organ or bone marrow transplants, and those undergoing chemotherapy treatment for cancer. People with compromised immune systems who become infected for the first time (primary infection) might experience the most severe symptoms and their CMV infection may remain active. Those who have been exposed to CMV previously may reactivate their infection. This could affect their eyes (causing inflammation of the retina, which can lead to blindness), digestive tract (causing bloody diarrhea and abdominal pain), lungs (causing pneumonia with a non-productive cough and shortness of breath), and brain (causing encephalitis). There can also be spleen and liver involvement, and those who have had organ or bone marrow transplants may experience some degree of rejection. Active CMV also further depresses the immune system, allowing other secondary infections such as fungal infections, to occur.

CMV Viral Test

Cytomegalovirus (CMV) testing is used to determine whether someone with signs and symptoms has an active CMV infection. Sometimes it may be ordered to help determine whether someone had a prior CMV infection.

CMV is a common virus that occurs widely throughout the population but rarely causes noticeable symptoms or significant health problems. However, primary CMV infection may cause serious illness and complications in newborns and people with weakened immune systems, such as transplant recipients, cancer patients, people receiving immunosuppressive drugs, and people with HIV.

There are a few different methods of detecting a CMV infection. The choice of tests and samples collected depends on the age of the person, their general health status and symptoms, and on the health practitioner’s clinical findings and suspicions of organ involvement.

Antibody testing (serology)

Antibody testing is done on blood samples and can be used to determine if someone has had recent or past exposure. There are two types of CMV antibodies that are produced in response to a CMV infection, IgM and IgG, and one or both may be detected in the blood.

  • IgM antibodies are the first to be produced by the body in response to a CMV infection. They are present in most individuals within a week or two after the initial exposure. IgM antibody production rises for a short time period and then declines. After several months, the level of CMV IgM antibody usually falls below detectable levels. Additional IgM antibodies are produced when latent CMV is reactivated.

  • IgG antibodies are produced by the body several weeks after the initial CMV infection and provide protection from primary infections. Levels of IgG rise during the active infection, then stabilize as the CMV infection resolves and the virus becomes inactive. After a person has been exposed to CMV, the person will have some measurable amount of CMV IgG antibody in their blood for the rest of their life. CMV IgG antibody testing can be used, along with IgM testing, to help confirm the presence of a recent or previous CMV infection.

CMV antibody testing may be used to determine immunity to primary CMV infections for people prior to organ or bone marrow transplantation and for a person diagnosed with HIV/AIDS. Since CMV infection is widespread and causes few problems to those with healthy immune systems, general population screening is rarely done.

Antibody testing and viral CMV detection may be used to help diagnose primary CMV infection in young adults, pregnant women, and some immune-compromised people with flu- or mononucleosis-like symptoms. By comparing the absence or presence of IgG and IgM antibodies in the same sample or the amount of antibody present in samples collected on different days, a health practitioner may be able to distinguish between active and latent CMV.

Direct Detection of CMV (CMV Viral Load)

Viral detection involves determining the presence of CMV in a blood, fluid, or tissue sample. This can be done either by culturing the virus or by detecting the virus’s genetic material (CMV DNA). Viral detection is used to diagnose congenital infections in newborns and may be used to detect and/or confirm active infections in others.

Viral culture is the traditional method of virus detection. Presence of the virus (positive cultures) can often be determined in as little as 1 to 2 days, but cultures that are negative for the virus must be held for 3 weeks to confirm the absence of CMV because the virus may be present in very low numbers in the original sample and/or the CMV strain may be slow-growing.

Molecular methods such as polymerase chain reaction (PCR) may be used to detect and measure the amount of viral DNA in a person’s sample. Testing can be qualitative, determining the presence or absence of CMV, or quantitative, measuring the amount of virus present.

Immune-compromised people with active CMV may be monitored using a variety of CMV tests. Often, health practitioners want a quantifiable viral test to be able to track the amount of virus present (viral load). They can use a quantitative test to monitor a person’s response to antiviral therapy.