- What is cytomegalovirus (CMV)?
CMV is a common virus from the family of herpes viruses. It is often the cause ofmononucleosis, pneumonia and other types of viral infections. Over 80% of the adult population has already been exposed to the CMV virus. CMV can be of clinical significance, especially in immunocompromised individuals, such as those who have had organ transplants, or who have had leukemia or HIV/AIDs. Most healthy people who are infected by CMV after birth have no symptoms, although some may develop symptoms of mononucleosis, the flu or a sore throat. Most CMV infections exhibit minimal or no symptoms, and thus go undetected.
The active CMV virus may be shed in bodily fluids of any infected individual, including urine, saliva, blood and semen. The shedding of the virus from cells into bodily fluids can occur intermittently, without any signs or symptoms of CMV infection.
A number of laboratory tests have been developed which can detect the presence of CMV antibodies. These antibodies develop following infection with CMV. Increase in the level of the IgM antibody is indicative of an active CMV infection. The IgG antibody develops after an active CMV infection. However, shedding of the virus and increase in IgM can occur at any time. Therefore, testing of total antibodies, as well as IgG and IgM separately, is done for blood and tissue donors. Persons who have been infected with CMV produce IgG antibodies to the virus which persist in that person’s body for their lifetime.
The testing of tissue donors, including semen donors, for CMV involves testing of the blood for total CMV antibodies, which include both IgG and IgM antibodies. The total antibody test only indicates that the person has been exposed to the CMV virus. An additional test is done for IgM antibodies and, if elevated, suggests and active infection.
- Interpretation of CMV status test results
A positive CMV IgG test shows that the person has had a past CMV infection or has been exposed to the virus. An IgM test that is positive indicates a current/active CMV infection. If the CMV IgG test is positive and the CMV IgM test is negative, it merely means that the person had been previously exposed to CMV. Note that once a person has had a CMV infection, the IgG test will always show positive, but if the IgM test is also positive, the person is actively shedding the virus and is once again positive.
- Significance of CMV and pregnancy
CMV can be transmitted from the mother to the fetus and can lead to congenital anomalies. It can be transmitted in semen to the female, and then to an embryo, fetus or a baby during pregnancy. Congenital CMV is the leading infectious cause of deafness, learning disabilities and intellectual disability in children.