Infectious erythema: antibodies to parvovirus B19 in blood

Infectious erythema is a disease caused by parvovirus B19 (B19V). This infection is also called "fifth disease" in addition to the four well-known TORCH infections ( toxoplasma, others, rubella, cytomegalovirus, herpes simplex - toxoplasma infection, rubella, cytomegalovirus infection, herpes infection). Depending on the age of the patient, infectious erythema is characterized by various symptoms: from erythematous rash and fever to severe forms of arthritis and lymphadenopathy. The infection is transmitted by airborne droplets (the incubation period is about 7 days), but infection can occur during blood transfusion or through the placenta from a pregnant woman to the fetus. Children aged 4-11 years are most often affected; in adults, infectious erythema is severe (especially in women over 30 years old). In pregnant women, parvovirus infection in the first and second trimesters of pregnancy causes hydrops fetalis (in 5-10% of cases) and leads to miscarriages and intrauterine fetal death (in 9-13% of cases). The greatest risk of developing these complications occurs when infection occurs between the 10th and 26th weeks of pregnancy.

Parvovirus B19 is a single-stranded DNA virus with a diameter of 18-24 nm that does not have an envelope. When a person is infected, the receptor for parvovirus B19 is the P-antigen, which is expressed on erythrocytes, erythrocytes, megakaryocytes, endothelial cells, placental cells, liver and fetal heart. Organs and tissues containing cells with the P-receptor become a target for parvovirus, which largely determines the specificity of the clinical manifestations of the infection. The frequency of P-antigen among native Europeans is 70-80%. Replication of parvovirus B19 occurs in erythrocytes of the bone marrow for 21 days. In the absence of P-antigen in humans, invasion and replication of the virus do not occur.

In all cases of parvovirus B19 infection, partial red cell aplasia of the bone marrow develops. Bone marrow aplasia leads to a decrease in the number of erythrocytes and the concentration of Hb in the blood, reticulocytopenia and anemia, the severity of which depends on the degree of aplasia. Usually, hematological blood parameters normalize within 10 days after the disappearance of fever, in some cases, signs of anemia can persist for up to 4 weeks. The number of platelets, lymphocytes and granulocytes also decreases. Subsequently, anemia is completely compensated for by the formation of new erythrocytes. After the infection, persistent lifelong immunity is formed, due to IgG antibodies. In individuals with immunodeficiency, regardless of its cause, persistence of the virus (the constant presence of viral DNA in tissues or blood) is most often noted, since the synthesis of antibodies to the B19 virus is impaired in them.

To diagnose parvovirus infection, IgM and IgG class antibodies are determined in the blood serum using the ELISA method.

IgM antibodies to parvovirus B19 are detected in 90% of patients 4-7 days after the clinical manifestations of the disease. The amount of antibodies gradually increases, reaching a maximum by the 4th-5th week, and then decreases. IgM antibodies to parvovirus B19 can persist in the blood for 4-6 months after the disease. Detection of IgM antibodies to parvovirus B19 in the blood serum during the acute period of the disease, and especially an increase in the antibody titer (as well as its decrease in the early stages after the infection) in the study of paired sera, confirm the diagnosis of infectious erythema (sensitivity - 97.6%, specificity - 97%). Pregnant women at risk of parvovirus B19 infection are shown periodic blood tests for IgM antibodies and AFP, as well as ultrasound scanning for the timely detection of fetal hydrops.

IgG antibodies to parvovirus B19 are detected in the blood 7-10 days after the onset of symptoms of the disease, their titer reaches a maximum after 4-5 weeks and remains elevated for many years. When studying IgG antibodies, only an increase in the antibody titer by at least 4 times indicates parvovirus infection (diagnostic sensitivity - 94%, specificity - 86%), since antibodies of this class can be detected in 50-70% of healthy adults. The presence of IgG antibodies to parvovirus B19 indicates immunity to the infection. When using recombinant VP2 capsid antigen in diagnostic kits, the diagnostic sensitivity of determining IgG antibodies to parvovirus B19 is 98.9%, specificity - 100%.

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