Rubella, IgG antibody avidity
Why this test?
To confirm or exclude a recent primary infection with the rubella virus;
to obtain data on the history of virus infection;
for differential diagnosis of recent cases of infection from previously transmitted forms or reinfection in people with an increased titer of IgG class antibodies in the blood;
to assess the risk of transmission of herpes infection to the fetus or newborn;
for differential diagnosis with contact dermatitis, erythema multiforme, measles, skin manifestations of syphilis, scarlet fever.
In what cases is it prescribed?
- If necessary, to assess the age of infection with the rubella virus; with positive and doubtful results of determination of IgM and IgG antibodies to the rubella virus;
- when examining pregnant women with suspicion of primary rubella virus infection;
- when planning a pregnancy - for the purpose of preventing infection of the fetus;
- in case of contact of a pregnant woman with a rubella patient.
Rubella is a viral anthroponotic disease characterized by fever, generalized lymphadenopathy and rashes on the skin (exanthema). The causative agent of the infection is the RNA-containing rubella virus of the family Togaviridae, genus Rubivirus.
The virus belongs to the group of causative agents 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.
The source of infection is a person suffering from a manifest or subclinical form of the disease, as well as a newborn with a congenital form of rubella within 1-6 months. The way of transmission of the virus from person to person is airborne. The incubation period of the disease is on average 12-18 days, but it can increase to 23 days. The main clinical manifestations of rubella include fever, generalized lymphadenopathy, especially involving the posterior cervical and occipital lymph nodes, small-spotted rash, conjunctivitis, rhinitis, pharyngitis.
The rash or rubella rash usually appears in the first three days of the illness on the face and neck, and then spreads over the whole body in a chaotic sequence within a few hours. When adults are affected, the disease proceeds in a more severe form.
Myalgia and arthralgia can be noted, often the disease can be complicated by pneumonia, otitis, encephalitis, meningoencephalitis. It is important to note the dangerous infection of rubella virus in pregnant women, especially in the first trimester of pregnancy. In this case, it can cause miscarriage, stillbirth and/or the development of the clinical picture of congenital rubella - a group of serious developmental defects that can cause deafness, cataracts, heart defects, hepatitis, microcephaly, signs of progressive impairment of the central nervous system.
Diagnosis of rubella is based on a comprehensive approach, taking into account clinical, epidemiological data and the results of laboratory examination. Laboratory serological diagnosis of rubella is based on the detection of antibodies to virus antigens. In the first days from the beginning of the infection, the production of antibodies of the IgM class begins, then their number increases during the first two to three weeks, and they can be detected more than seven months after an acute infection.
The production of antibodies of the IgG class begins 2-4 weeks after infection, increases for several weeks, then falls to a certain level. After the disease, IgG class antibodies to the rubella virus remain in a person for the rest of his life. Detection of IgG class antibodies may indicate the presence of transferred or current rubella, the presence of an immune response to the rubella virus, which was formed after the transferred disease, as a result of vaccination or when antibodies are transferred from the mother to the fetus during pregnancy.
An additional study in the diagnosis of rubella is the determination of the avidity of IgG class antibodies to virus antigens. Avidity of antibodies characterizes the strength of binding of specific antibodies to antigens of the pathogen. This makes it possible to determine the degree of effectiveness of the specific interaction between molecules of antibodies and antigens, the rate of formation of immune complexes and the completeness of neutralization of antigens.
Determination of the avidity of IgG class antibodies is necessary for obtaining data on the history of primary infection and differential diagnosis of recent cases of infection from previously transferred forms or reinfection in people with an increased titer of IgG class antibodies in the blood. 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-affinity 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 during the period of reactivation (exacerbation) of the infection.
It is important to note that the study is carried out with positive results of detection of antibodies to the rubella virus of the IgG class. In newborn babies, 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 a test for avidity.