Infectious erythema: antibodies to parvovirus B19 in the blood

Infectious erythema is a disease caused by parvovirus B19 (B19V). This infection is also called the "fifth disease" in addition to the four well-known TORCH infections ( toxoplasma, others, rubella, cytomegalovirus, herpes simplex - toxoplasma infection, rubella, cytomegalovirus infection, herpetic 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. Infection is transmitted by airborne droplets (the incubation period is about 7 days), but infection can occur with blood transfusions or through the placenta from pregnant to the fetus. Most often, children 4-11 years old fall ill, in adults infectious erythema is very difficult (especially in women older than 30 years). In pregnant women, parvovirus infection in the first and second trimesters of pregnancy causes fetal hydrops (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 with infection between the 10th and 26th weeks of pregnancy.

Parvovirus B19 is a single-stranded DNA-containing virus with a diameter of 18-24 nm, which does not have a membrane. When a person becomes infected with a receptor for parvovirus B19, the P-antigen becomes apparent, which is expressed on erythrocytes, erythrocaryocytes, megakaryocytes, endothelial cells, placental cells, liver and fetal heart. Organs and tissues containing cells with P-receptor, become a target for parvovirus, which largely determines the specificity of clinical manifestations of infection. The frequency of P-antigen among the indigenous inhabitants of Europe is 70-80%. Parvovirus B19 replication occurs in erythrocarytes of the bone marrow for 21 days. In the absence of a human P-antigen, there is no invasion or replication of the virus.

In all cases of infection with parvovirus B19, partial red cell aplasia of the bone marrow develops. Aplasia of the bone marrow 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 counts are normalized within 10 days after the disappearance of fever, in some cases signs of anemia can persist up to 4 weeks. The number of platelets, lymphocytes and granulocytes also decreases. In the future, anemia is fully compensated for by the formation of new red blood cells. After the transferred infection, a stable lifelong immunity is formed, caused by antibodies of IgG class. In individuals with immunodeficiency, regardless of its cause, the most frequent is the persistence of the virus (the constant presence of DNA of the virus in tissues or blood), as the synthesis of antibodies to the B19 virus is disturbed.

For the diagnosis of parvovirus infection, antibodies of IgM and IgG classes in serum are determined by ELISA.

Antibodies IgM to parvovirus B19 are detected in 90% of patients 4-7 days after clinical manifestations of the disease. The number of antibodies gradually increases reaching a maximum by 4-5 weeks, and then decreases. Antibodies IgM IgM to parvovirus B19 can persist in the blood for 4-6 months after the disease. The detection of IgM antibodies to parvovirus B19 in the blood serum during the acute period of the disease, and especially the increase in the antibody titer (as well as its decrease in the early periods 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 periodic blood tests for IgM and AFP antibodies, as well as ultrasound scanning for the timely detection of fetal dropsy.

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. In the study of IgG antibody, only an increase in antibody titer of at least 4-fold suggests parvovirus infection (diagnostic sensitivity is 94%, specificity is 86%), since 50-70% of an adult healthy population can detect antibodies of this class. The presence of IgG antibodies to parvovirus B19 indicates the presence of immunity to infection. When used in diagnostic kits of recombinant VP2 capsid antigen, the diagnostic sensitivity of the detection of IgG antibodies to parvovirus B19 is 98.9%, specificity is 100%.

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