Parvovirus is an anthroponotic disease caused by a DNA-containing virus. It is often asymptomatic. It can manifest as a general intoxication syndrome, catarrhal phenomena, dyspeptic symptoms and rash. For adults, the presence of signs of arthritis is characteristic. With transplacental transmission of the pathogen, nonimmune fetal dropsy develops, miscarriages are possible in the early stages. Diagnosis is based on the detection of specific antibodies. PCR is used, and general clinical research methods are additionally prescribed. Specific treatment has not been developed, symptomatic therapy is being carried out.
B34.3 Unspecified parvovirus infection
Human parvovirus B19 was discovered in 1975 during a patient’s blood test on HBsAg. The pathogen was detected in well 19 of panel B of the blood sample, which served as the basis for the name of the virus. The infectious agent is widespread everywhere, an asymptomatic course is often observed. Children aged 1-10 years are more susceptible to parvovirus infection (infectious erythema, the “fifth disease”). Resistance to infection in children under one year is explained by the presence in the child’s blood of the corresponding antibodies received from the mother. The most severe variants of the course of the pathological process among the adult population are more common in women. Seasonality is characteristic. Outbreaks of morbidity are registered from the end of winter to the beginning of spring in organized collectives.
The causative agent is a DNA–containing virus in 19 of the family Parvoviridae. The pathogen is quite stable in the external environment, insensitive to freezing, exposure to a variety of disinfectants (ether, alcohol), withstands heating up to 56 ° C for an hour. Such properties are due to the absence of a lipid component in the capsid of the virus. The virus is instantly inactivated by boiling, using formaldehyde, hypochloride for disinfection.
The source of infection is a sick person. Most often, infection occurs by airborne droplets. It is possible to implement a vertical pathway when the virus enters from the mother to the fetus through the placenta, a hemocontact mechanism during transfusion of infected blood components, especially VΙΙΙ and IΧ coagulation factors, as well as during transplantation of infected organs and tissues. The patient is contagious before the rash appears. Viremia is characteristic of this period, in addition, the pathogen is found in the secret of the upper respiratory tract.
The pathogenesis of parvovirus infection has not been sufficiently studied. It is believed that the main link in the development of the disease is the defeat of the progenitor cells of erythrocytes. The place of primary reproduction of the pathogen has not been established. 7-8 days after contact with the source of the disease, the virus penetrates into the blood and red bone marrow. The cause of the lesion of red germ cells is the presence on their surface of a specific P-protein, thanks to which the infectious agent is able to penetrate into the cells, causing their lysis. P-protein is also located on the surface of endothelial cells, trophoblast, chorionic villi, megakaryocytes, hepatocytes.
People with a birth defect or lack of this protein are immune to parvovirus. The long-term persistence of the pathogen in individuals with immunodeficiency conditions contributes to the aplasia of the corresponding cell culture. Erythropoiesis is suppressed, the number of erythrocytes, reticulocytes, hemoglobin decreases, anemia develops. One of the clinical symptoms of infection is the presence of a rash and the occurrence of arthritis. Such conditions are explained by the formation of immune complexes, their deposition in the skin and synovial membrane.
According to the severity of the course, depending on the severity of intoxication, mild, moderate and severe degrees of the disease are distinguished. According to the duration, there are acute (up to 1 month), subacute (up to 3 months) and chronic, recurrent or continuous (over 3 months) variants of the course. There are the following forms of the pathological process:
- Congenital infection. It is formed as a result of the transmission of the virus by the transplacental route. The risk of infection of the fetus is 30%. The most dangerous period is the period from 10 to 28 weeks of gestation. Stillbirth, according to various data, occurs in 3-8% of cases. Cases of miscarriage, intrauterine fetal death were noted during the transmission of parvovirus transplacentally. The main cause of developmental disorders is hypoxia due to a decrease in the oxygen capacity of the blood. Viral myocarditis with rhythm disturbances, heart failure is often observed, and hypoalbuminemia is detected when liver cells are affected.
- Acquired infection. It is more often diagnosed in children. Women prevail among adult patients. In pregnant women, the clinical picture has no specific features. Acquired parvovirus infection is divided into typical and atypical (arthralgic, hepatitis, asymptomatic) forms.
- Chronic infection. Develops in patients with primary or acquired immunodeficiency. Occurs due to the inability of the human body to eliminate the virus. Permanent viremia is typical. The pathogen is found in the red bone marrow.
The incubation period is about 2 weeks, with a maximum of 20 days. In the typical form of acquired parvovirus infection, mainly occurring in children and adolescents, in the prodromal period, there is a feeling of weakness, malaise, subfebrile fever. Headaches, arthralgia, myalgia, nausea, diarrhea, pharyngitis, rhinitis are detected. After 3-5 days, the first elements of a rash appear on the cheeks against the background of diffuse erythema of the face – edematous erythematous plaques, a symptom of a “slap”. The nasolabial triangle remains pale.
Then the rash spreads throughout the body. The elements tend to merge, the rash is often accompanied by itching. The most typical localizations are extensor surfaces of the limbs, neck, trunk. After 5-10 days, the rashes begin to pale in the center, acquiring a characteristic lace appearance. Gradually, the rash disappears without peeling, but provoking factors (hot baths, solar irradiation) they can cause its relapse. After recovery, lifelong immunity is formed.
Joint damage and the development of arthralgic form is typical for women. The course of arthritis is benign. The metacarpophalangeal, interphalangeal, ankle, knee joints are mainly involved. They are bothered by pain when moving. Local soreness, swelling, hyperemia of the periarticular areas is determined. Recovery occurs after 1-3 months. Destructive changes are uncharacteristic. Cases of acute hepatitis (hepatitis form) with infection with parvovirus have been described. Intoxication is detected with the presence or absence of mild jaundice, a moderate increase in the activity of hepatic transaminases and a slight increase in the size of the liver.
The asymptomatic form of acquired infection is characterized by an increase in the titer of specific antibodies in the blood serum without clinical manifestations. The virus is secreted with the secret of the respiratory tract, so patients are contagious. In 1990, the defeat syndrome was described “by the type of gloves and socks” when infected with parvovirus B19. In this form, the presence of fever, myalgia, arthralgia, edema of the distal extremities with a clear border of rashes in the ankles and wrists is noted. Symptoms disappear within 2 weeks.
Since the pathogenesis of infection is associated with the suppression of red blood germ, complications are most often observed in patients with hemolytic anemia (thalassemia, sickle cell anemia, pyruvate kinase deficiency). An aplastic crisis develops. There are no reticulocytes in the blood, the number of red blood cells and the level of hemoglobin sharply decreases. There is pronounced weakness, shortness of breath, tachycardia, confusion. The crisis lasts 7-12 days. Full recovery of blood counts occurs in a month. In the absence of specific treatment, the mortality rate is 2.2%. There is evidence of the ability of parvovirus to cause meningitis, encephalitis.
Objectively, there are specific elements of a rash with appropriate localization, pallor of the nasolabial triangle, with the development of arthralgic form – swelling, hyperemia of the affected joints, with hepatitis – jaundice, liver enlargement. The following clinical and laboratory methods are used to diagnose parvovirus infection:
- Blood test. Mild anemia, thrombocytopenia, neutropenia, acceleration of ESR are determined. Aplastic crisis is characterized by severe anemia with a critical decrease in hemoglobin content, absence of reticulocytes.
- Identification of infectious markers. Serological techniques are used. IgM and IgG titers are determined. IgM appears in the blood 7-10 days after infection and circulates for up to 6 months. IgG is formed 2-3 days after the appearance of IgM. Thus, the IgM level is not a strict indicator of acute parvovirus infection. Usually, an increase in the IgG titer is used in dynamics. PCR diagnostics has been developed.
Differential diagnosis is carried out with scarlet fever, measles, rubella. In some cases, differentiation with allergic reactions, Kawasaki disease, Rocky Mountain fever is required. With the predominance of gastrointestinal symptoms, the disease is distinguished from pseudotuberculosis, enterovirus infection. With the development of hepatitis, it is necessary to exclude other possible causes of the pathological condition. The arthralgic form may resemble rheumatoid arthritis, joint damage in Lyme disease.
Drugs for etiotropic treatment have not been developed. Symptomatic therapy is prescribed. In the case of severe fever, antipyretics are used, with severe itching, antihistamines are used. Detoxification therapy is carried out. In case of aplastic crisis, urgent transfusion of erythrocyte mass is necessary under the control of the data of the blood test. Repeated hemotransfusions are possible until the restoration of its own erythropoiesis. Additionally, oxygen therapy is indicated. In chronic parvovirus infection, the use of intravenous immunoglobulin gives good results. Withdrawal of medications or correction of conditions that caused immunodeficiency is required. During the formation of fetal dropsy, intrauterine exchange transfusions are possible.
Prognosis and prevention
The forecast is relatively favorable. The infection has a benign course, with the exception of cases of intrauterine infection of the fetus and the development of pathology in patients with hemolytic anemia, immunodeficiency. The tactics of conducting in these states are determined individually. Dispensary follow-up after the disease is not carried out. Specific prevention has not been developed, the vaccine is at the stage of clinical trials. Isolation is not required, since patients are contagious only before the appearance of rashes. Screening of pregnant women for parvovirus infection has not yet been carried out, it is necessary to develop measures aimed at identifying seronegative pregnant women and preventing their infection.