CMV: the most common infectious cause of birth defects

Montreal - Although cytomegalovirus is a virus that is completely unknown to the general public and under-recognized by physicians, it is nevertheless the most common infectious cause of fetal birth defects in the Canadian population. An entire month is dedicated to raising awareness among pregnant and childbearing patients and perinatal care providers.

Cytomegalovirus (CMV) is a member of the herpes family and can infect anyone. The virus remains dormant in the body for life following an infection, but it can be reactivated, especially in people who are immunocompromised by certain therapies, for example. It is also possible to be re-infected multiple times, as several strains of CMV exist. Most people are unaware that they have been infected, as the virus rarely causes symptoms or problems in healthy people. However, pregnant women should be aware that CMV infection can be transmitted to their fetus.

In fact, CMV is the most common cause of in utero infections, occurring in 0.2% to 2.2% of all live births. One in 200 babies in Canada is infected with CMV during pregnancy, and 20% of children with a diagnosis of congenital CMV will have permanent neurological sequelae, such as deafness, intellectual retardation, complete or partial blindness and developmental disabilities. However, in 80% of cases, infected children are asymptomatic and will not develop long-term health problems. 

In Canada, 40% to 60% of pregnant women have had CMV, but in the majority of cases, the virus will not pose a problem during pregnancy. It is at the time of infection that the virus is most dangerous, whether it is a primary infection, an infection with a new strain, or when reactivation is significant enough that the virus is circulating in the bloodstream. 

How can women be protected? 
CMV can have serious consequences on the health of the fetus, which demonstrates the importance of educating pregnant women about prevention, especially since the steps to take are very simple. 

The virus is transmitted through contact with body fluids, mainly urine and saliva. To protect themselves, CMV Canada recommends that pregnant women wash their hands frequently, avoid sharing utensils, drinks and food with young children, avoid putting their baby's pacifier in their mouth, avoid kissing their child on the mouth, and clean all surfaces and toys that may have come in contact with the child's fluids often. 

"Prevention methods are not well explained to women," explained Dr. Isabelle Boucoiran, an obstetrician-gynecologist at CHU Sainte-Justine. "I often see women whose babies have been diagnosed, but who have never heard of the virus. And that's a big problem. Educating women about CMV and how to protect themselves from it has been shown to reduce the risk of infection. Women rely on their primary care physician to give them this kind of message. With the new guidelines, which I co-authored, and the SOGC's communications on this topic, healthcare professionals will be more alert." 

CMV screening is not routine
The SOGC's latest recommendation states that screening can be offered to women at highest risk, including those who are pregnant and living with a child under the age of three, as well as women who are considering pregnancy and have repeated contact with young people of that age. A pregnant woman living with an infected child has a one in four chance of becoming infected, as young people excrete the virus a lot without necessarily showing symptoms.

"One of the issues with CMV testing," continued Dr. Boucoiran, who is also a member of the SOGC's infectious disease committee, "is that our tests are able to detect primary infection with IgG and IgM serologies and an avidity test, but not reinfection with a new strain or reactivation of the old strain." 

However, she tells us, avidity testing is available in several provinces, including Quebec, but not across the country. "It's a real issue: you can't screen if you don't have that test, because IgG and IgM alone are not reliable enough to identify primary infections." 

Most diagnoses of CMV in pregnancy have been made because the physician screened or because antenatal ultrasound abnormalities were detected, but which do not necessarily indicate severe involvement. 

The earlier the infection is detected in pregnancy, the greater the benefit to the fetus. 

"The woman can undergo treatments to try to minimize the severity of the damage to the fetus, although they are still experimental," Dr. Boucoiran reminded. "If there is a suspicion or confirmed infection during pregnancy, we can confirm it at birth and put in place treatments such as specific antiretrovirals and strategies for hearing development, for example. That kind of intervention changes everything for the child's long-term development. In Ontario, they have been routinely screening all newborns for congenital CMV infection for about a year." 

Originally ran on our sister brand in Quebec, Profession Santé. Translated from French.