Cytomegalovirus, CMV also known by the acronym, is one of the herpes family of viruses, extremely common, capable of causing an infection called cytomegalovirus. In some populations, especially in developing countries, the number of adults who have had contact with the virus approaches 100%. Even in countries such as Finland and the United States, the percentage of adults infected with CMV is greater than 80%.
Despite being a highly contagious virus and with very high rates of infection among the population, the fact is that most people do not even suspect that has been contaminated with cytomegalovirus. This occurs because cytomegalovirus infection is a very soft, virtually asymptomatic, most persons having a healthy immune system.
If the CMV in healthy individuals is practically harmless, the same can not be said for immunosuppressed patients or pregnant women. CMV infection during pregnancy does not usually cause symptoms in the mother, but it is very dangerous to the fetus, because it is associated with an increased risk of congenital malformations or severe infection in early life.
In this article we will explain the consequences of cytomegalovirus infection during pregnancy. We will also address ways of transmitting the virus, which means the IgG and IgM serology for cytomegalovirus and what can be done when a mother is contaminated during pregnancy.
As mentioned in the introduction of the article, the great problem of cytomegalovirus infection during pregnancy is not in relation to the mother's health, but the risk of complications to the fetus.
There are two ways to have cytomegalovirus, the most common is called primary infection, which occurs when an individual who has never had contact with the CMV infects up for the first time. Once infected by CMV, our immune system creates antibodies that can neutralize the virus, preventing their replication. However, as with other herpes family of viruses, the virus is neutralized, but not completely eliminated from the body. If over the years the patient experience a weakening of their immunity, CMV may be able to reactivate, returning to multiply. This reactivation of the virus in someone who already had the disease years ago is the second possible way to have cytomegalovirus.
The risk of fetal infection is much higher in cases of primary infection during pregnancy than in the reactivation of the virus. In fact, while 40% of babies of mothers who had a primary infection during pregnancy are born infected by CMV, only 1% are born infected when the previously infected mother has a reactivation of the virus during pregnancy.
The vast majority of CMV-infected infants are infected during pregnancy, because the virus is able to multiply in the placenta and infect the fetus. There are, however, other forms of baby contamination, for example during vaginal delivery, due to contact with maternal blood and secretions, or during the first days of life by transmission of the virus by maternal milk.
Regarding the mother, contamination of gives like any other individual. Cytomegalovirus can be found in various parts of the body, including urine, blood, airway secretions, vaginal secretions, semen, feces, tears and breast milk. In this way, transmission can occur through sexual intercourse, close contact due to transmission through the airways, blood donation, prepared foods with poorly sanitized hands, etc.
There is evidence that the CMV respiratory secretions can survive in the environment for variable periods depending on the surface. For example, CMV can remain viable for metal and wood for one hour, glass and plastic for three hours, and rubber cloth and cookie for up to six hours.
The symptoms of congenital CMV infection depend on the route of transmission and trimester of pregnancy that occurred contamination. The lower the gestational age, the greater the chances of serious injury of the fetus.
90% of babies infected with CMV during pregnancy are born without any signs or symptoms. However, up to 15% of children who apparently have no problems may have progressive hearing loss, which in most cases is unilateral, but it can also affect both ears. Hearing screening programs in early life can get early identification of some of these newborns infected with CMV. However, the hearing loss associated with congenital cytomegalovirus infection can arise only after several months or years.
Approximately 10% of congenitally infected newborns CMV infection symptoms already present from birth. In addition to the progressive hearing loss, other early manifestations of CMV in newborns are small babies, hepatosplenomegaly (enlargement of the liver and spleen), anemia, petechiae and purpura (small purplish spots on the skin) and jaundice ( yellowing of the skin). At least two thirds of newborns with congenital CMV infection have symptomatic neurologic involvement, including microcephaly, seizures, brain abnormalities and feeding difficulties. Serious eye changes are also very common.
Babies and infected late in pregnancy or childbirth often born healthy, however, can develop the first symptoms of CMV from the 3rd week of life. Some babies, however, take up to six months to show the first signs and symptoms of cytomegalovirus.
As the baby early in life has a very immature immune system, it is very likely to have a severe form of cytomegalovirus. Possible problems are liver lesions, anemia, pneumonia and necrotizing colitis.
Serology examination is the name used to identify the presence of certain antibodies in our blood. Serology is an indirect method of identifying an infection. Since we can only develop antibodies against germs that have infected us, have positive serology against CMV, for example, means the patient has already had CMV infection at some point in life (even though the disease has been completely asymptomatic).
The serological survey two types of antibodies, immunoglobulin G (IgG) and immunoglobulin M (IgM). When we contacted first with any microbes, the immune system produces relatively quickly, within a few days, IgM antibodies. The acute phase IgM is an antibody present during the active phase of the infection. After curing, the immune system will produce another type of antibody, IgG. The IgG antibody is a memory used by the body to prevent the patient from being infected again by the same microbe. Therefore, having IgM circulating in the blood is a sign of disease in the acute phase, while having reagent IgG indicates that the patient has had the disease in the past and now is immune to it.
Most of the infections, the logic of IgM and IgG antibodies is simple, as just explained. In cytomegalovirus, however, the situation is somewhat more complex.
In the case of CMV infection, early IgM antibodies appear within 2 weeks and can take up to 12 months to disappear. This means that a pregnant two months can make serology, find positive IgM antibodies, but not having been infected with CMV during pregnancy, but months earlier. If the mother has not had symptoms, it is difficult to know if CMV infection is recent or occurred several months ago.
The dosage of IgG antibodies help a little to clarify the situation. The first IgG antibodies appear about 3 weeks after infection, increase concentration for a few weeks and then stabilize, to always remain detectable in the blood. So if the mother does two IgG doses 4 weeks apart and the value increases about 4 times from one to another, this is a recent sign of infection. Conversely, if the IgG reagent values are similar 4-week interval, this means an IgG already in steady state, which indicates past infection.
But the confusion is not over yet. In patients with CMV reactivation, the titers of IgM and IgG antibodies can be raised in the same way as occurs in primary infection. So if previous serological status of pregnant women is not known, the fact that she had an IgM reagent does not help much, as this may mean:
1. Old infection, which occurred several months ago, but still have circulating IgM positive.
2. Recent primary infection and, therefore, risk to the fetus problems.
3. Reactivation of an old CMV, a situation that carries a lower risk of complications for the baby than the primary infection.
For the reasons explained above, many obstetricians do not routinely ask against CMV serology, if pregnant women are completely asymptomatic. In fact, despite the serology can create some confusion, especially come to be IgM positive, it can be useful in the opposite situation, ie when the mother has a negative IgM and IgG positive. In this case, it means that the pregnant have had CMV in the past, there is a very low risk of developing it cytomegalovirus during pregnancy.
There is no proven effective treatment to prevent the occurrence of disease in the fetus if the mother CMV-contaminate during pregnancy. Fortunately, in most cases, even when the mother is contaminated in the first quarter, babies are born healthy.
