Cytomegalovirus, IgG antibody avidity

Why this test?

For diagnosis of CMVIII;

to determine the term of primary infection with cytomegalovirus;

to obtain data on the history of cytomegalovirus infection;

for differential diagnosis of primary infection from the chronic form and the active form of CMVI in the period of reactivation (exacerbation) of persistent infection; to confirm or exclude recent cytomegalovirus infection of pregnant women or women planning to become pregnant in the complex laboratory diagnosis of CMVI.

In what cases is it prescribed?

• In case of suspicion of CMVI and its clinical manifestations; if necessary, estimate the duration of CMVI and the history of cytomegalovirus infection;
• when determining the date of primary infection and obtaining data on the history of cytomegalovirus infection;
• if CMVI is suspected in pregnant women;
• when planning a pregnancy - to prevent infection of the fetus;
• when examining children born to mothers with CMVI (it is recommended to conduct research in children older than six months of age);
  with positive results of determination of antibodies to cytomegalovirus classes IgM and IgG.

Test information

Cytomegalovirus (Cytomegalovirus) belongs to the family of human herpes viruses, genus Cytomegalovirus, and is the causative agent of cytomegalovirus infection.

This is a widespread human infection, characterized by a mild, asymptomatic course in people under normal conditions, with a normally functioning immune system.

It acquires special clinical significance in persons with pathology of the immune system, immunodeficiency states and in pregnant women due to the risk of intrauterine infection of the fetus. The cytomegalovirus carrier is determined in 60-90% of the adult population. CMVI belongs to the group of TORCH-infections (translation of the first letters of the Latin Toxoplasma - Toxoplasma, rubella - Rubella, cytomegalovirus - Cytomegalovirus, herpes - Herpes), which are potentially dangerous for the development of the fetus and cause severe organ damage in newborn children.

Cytomegalovirus can be detected in 0.2-2.2% of newborns and is the leading cause of congenital infections worldwide. Approximately 10% of such children develop clinical signs of the disease from birth, in part - during the first ten years of life.

Cytomegalovirus belongs to DNA-containing viruses. It has the ability to slowly spread in the culture of infected cells, changing and increasing the size of cells (the phenomenon of cytomegaly). The source of infection is a person who sheds the virus through various biological fluids.
These include blood, saliva, urine, breast milk, cervical and vaginal secretions, seminal fluid, cerebrospinal fluid, contents of the gastrointestinal tract, and other secretions.

The infection is transmitted by airborne, contact, sexual means, as a result of a blood transfusion from an infected donor.
Infection during organ transplantation and a vertical route of transmission, from an infected woman to a child during pregnancy or childbirth, are also possible. The duration of the incubation period of the disease is often impossible to establish, since most clinical cases are not recognized and proceed in a latent, asymptomatic form. It should be noted that CMVI is characterized by long-term persistence of the pathogen in the human body.
This leads to the fact that many people are carriers of this type of infection for many years and possibly for a lifetime. When the immune system is weakened, a severe course of the disease may be noted. Acquired and congenital forms of CMVI are distinguished.

The acquired form of infection occurs as an acute localized process, similar in clinical symptoms to acute respiratory viral infection or infectious mononucleosis. There is an increase in body temperature, weakness, general malaise, sore throat, myalgia, and an increase in cervical lymph nodes.
In rare cases, complications in the form of arthralgias, arthritis, pneumonia, and cytomegalovirus hepatitis are noted. In children up to three months of age, as well as in persons with immune system pathology (immunodeficiency states, HIV infection, after organ transplantation, treatment with immunosuppressive drugs, with malignant diseases), CMVI can proceed in a severe form with the development of serious complications.

At the same time, severe damage to the lungs, kidneys, liver, gastrointestinal tract, nervous system with the development of viral encephalitis develops. The congenital form of CMVI can occur as a result of transplacental transmission of infection from the mother to the fetus when a woman is infected in the early stages of pregnancy, immediately before pregnancy.
There is a special danger of infection in case of primary infection of a woman during pregnancy. At the same time, the woman lacks immunity to cytomegalovirus and, therefore, the child's health is not protected. Acute congenital CMVI develops, which leads to spontaneous abortion or death of the embryo.

When the fetus is damaged in the later stages of pregnancy, a hemorrhagic syndrome develops with hemorrhages in the skin, internal organs, and brain. Encephalomalacia, cerebral calcification, enlargement of the spleen, liver, and hepatitis are noted. It is also possible to infect the child during childbirth when passing through the birth canal.

Chronic congenital CMVI causes fibrosis of internal organs and malformations: hydrocephalus, microcephaly, uveitis, blindness, heart defects, sensorineural hearing loss, and other neurological disorders.

There is also a delay in neurological and mental development. The diagnosis of CMVI is complex and is based on a combination of anamnestic, clinical data and the results of laboratory tests.

Due to the fact that clinical diagnosis of CMVI is difficult in most cases, laboratory diagnostic methods are of great importance. Antibodies of the IgG class to cytomegalovirus appear 2-4 weeks after infection, their level in the blood persists for several years and can serve as a sign of a transferred disease. This class of antibodies can be detected during primary infection, exacerbation of the chronic form of infection, and persistent and latent forms of CMVI.

Determination of the avidity of IgG class antibodies to cytomegalovirus antigens is important in the diagnosis of CMVI. The avidity of antibodies characterizes the strength of binding of specific antibodies to pathogen antigens.

Determining the avidity of antibodies of the IgG class is necessary to obtain data on the history of infection, possible determination of the duration of the course of CMVI and the term of primary infection. This is due to the fact that in the first three to four months after infection, antibodies with low avidity are synthesized, that is, they have a weak antigen binding strength.

Then the production of antibodies with borderline (medium) avidity and high-avidity antibodies begins. Low-avid antibodies indicate primary infection and infection within the last three to four months. Detection of antibodies with medium avidity indicates the presence of antibodies with both low and high avidity.

The determination of antibodies with high avidity indicates the antiquity of the transferred infection at least three to four months back before the time of the study.

Antibodies with high avidity are also determined in the case of an active form of CMVI during the period of reactivation (exacerbation) of persistent infection. It is important that in newborn children in the first six months of life, it is possible to detect maternal antibodies of the IgG class in the blood, which makes it difficult and in some cases impractical to conduct this test for avidity.

In people with pathology of the immune system, immunodeficiency states, HIV infection, the test result may be unreliable due to a low level of IgG class antibodies. In this case, it is recommended to carry out additional tests to detect CMVI.
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