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Objective was to investigate the SARS-CoV-2 collective immunity status of the population of Belarus within the context of the COVID-19 pandemic. Materials and methods. The work was carried out according to the methodology for assessing SARS-CoV-2 population immunity, developed by Rospotrebnadzor Russia and the Ministry of Health of Belarus with the participation of the St. Petersburg Pasteur Institute, taking into account WHO recommendations. The Bioethics Committee of Belarus and the local ethics committee of the St. Petersburg Pasteur Institute approved the study. Selection of participants was carried out using a questionnaire method and online technology (internet, cloud server). Volunteers were randomized into seven age groups (years of age): 1–17; 18–29; 30–39; 40–49; 50–59; 60–69; and 70+. Regional randomization ensured proportional representation of volunteers from each region, and no more than 30 people were included from one enterprise. In accordance with manufacturer instructions, blood plasma samples were analyzed for: IgG antibodies (Abs) to the SARS-CoV-2 nucleocapsid (Nc) using a quantitative ELISA test system; and IgG Abs to the receptor binding domain (RBD) of the SARS-CoV-2 S (spike) surface glycoprotein using a qualitative ELISA test system. Statistical processing was carried out using Excel 2010 and other software. Statistical differences were designated as significant when p < 0.05, unless otherwise indicated. Results. The level of seroprevalence, in terms of Abs to Nc among the Belarusian population, was 38.4% (95% CI 37.6–45.4). The highest Ab levels were found among individuals in older age groups (50-70+ years old). The lowest were found in children 1–17 years old and in young people 18–39 years old The distribution of seroprevalence across Belarusian regions was relatively homogeneous, with the exception of the Minsk Region, where a statistically significant decrease in the indicator was noted. In terms of profession, the largest share of seropositive individuals was found among transportation workers; the smallest was found in business. The moderate COVID-19 incidence has not led to a dramatic increase in the number of contacts. The base reproduction number (R0) was 1.3. In the Republic of Belarus, there was a moderate level of asymptomatic COVID-19 among seropositive individuals (45.3% [95% CI 44.0–46.7]). This form of infection was observed most often among children aged 1–17 years old (65.0% [95% CI 61.3–68.6]). In parallel with seroprevalence assessment, SARS-CoV-2 vaccination was carried out. We used two vaccines: Gam-COVID-Vac (also known as Sputnik V, developed by Gamaleya National Center for Epidemiology and Microbiology, Russia); and BBIBP-CorV (Sinopharm, PRC). Vaccination against SARS-CoV-2 was accompanied by an increase in the level of anti-RBD Abs (95% [95% CI 94.7–96.7]). Taking into account the vaccination of a subset of the population with BBIBP-CorV, the overall herd immunity, inferred from the analyzed indicators (presence of anti-Nc or anti-RBD Abs), was 47.1% (95% CI 46.3–48.0). Conclusion. COVID-19 in Belarus was characterized by a moderately pronounced course of the epidemic process. The threshold level of herd immunity to SARS-CoV-2 has not yet been reached, as a result of which the conditions for progression of the epidemic remain.

A case of long-term persistence of parvovirus B19 is described for the first time in a patient with Gilbert's syndrome against the background of immunodeficiency with predominance of infectious symptoms (chronic herpesvirus infection). Previously, the patient (male, 48 years old) was diagnosed with Gilbert's syndrome, chronic rhinosinusopharyngitis, and chronic herpesvirus infection. In July 2017, parvovirus B19 DNA was detected in blood. No clinical manifestations of infectious erythema were noted. The patient was admitted to the medical center of St. Petersburg Pasteur Institute. His blood samples obtained under informed consent were examined at the medical center in Central Clinical and Diagnostic Laboratory of St. Petersburg Pasteur Institute in January and June 2018 and in November 2019. ELISA test systems “Anti-Parvovirus B19 ELISA (IgM)” and “Anti-Parvovirus B19 ELISA (IgG)” (Euroimmune, Germany), as well PCR reagent kit “AmpliSens Parvovirus B19-FL” (FSB Central Research Institute of Epidemiology of Rospotrebnadzor, Russia) were used for specific diagnostics. Interferon status was determined by the induced production of IFN types I, II and circulating (serum) interferons. Moreover, we considered the laboratory data obtained earlier at different medical facilities of St. Petersburg. IgM class antibodies to the parvovirus B19 were not detected in the blood samples obtained in 2018. IgG antibody titer was 96 IU/ml and 264 IU /ml, respectively. Parvovirus B19 DNA was isolated from blood plasma, but the viral load was less than 720 IU of PVB19 DNA/ml (1.5 x 102 and 1.9 x 102 copies of DNA/ml, respectively). Clinical blood analysis, showed only minor (no more than 7%) deviations from the reference values, increased hemoglobin saturation of red blood cells (RBC), a decreased width of RBC distribution curve, and relative lymphocytosis. A deficiency of various interferon types was revealed: IFNγ level was 80 IU/ml in both samples, IFNα, IFNβ amounts varied from 80 to 160 IU/ml, respectively. The period of parvovirus B19 DNA persistence in blood was 11 months in presence of immunodeficiency. The patient was administered drugs of the interferon group. Parvovirus B19 DNA was not detected in clinical samples of November 2019; IFNα, IFNβ and IFNγ values were 160 IU/ml. We have detected recovery of lymphoid cell ratio, increase in their number, and improved indexes of interferon status.

The first case of COVID-19 was diagnosed in St. Petersburg on March 2, 2020; the period of increase in the incidence lasted for 10 weeks, the maximum rates were recorded in mid-May, and subsequently there was a statistically significant decrease in the incidence.Objective: to determine the level and structure of community immunity to SARS-CoV-2 among the population of St. Petersburg during the period of intensive spread of COVID-19.Materials and methods. Selection of volunteers for the study was carried out through interviewing and randomization. The exclusion criterion was active COVID-19 infection at the time of the survey. 2713 people aged 1 to 70 years and above were examined for the presence of specific antibodies to SARS-CoV-2. Antibodies were detected by enzyme immunoassay.Results and discussion. Studies have shown that in St. Petersburg, in the active phase of COVID-19 epidemic, there was a moderate seroprevalence to SARS-CoV-2, which amounted to 26 %, against the background of a high frequency (84.5 %) of asymptomatic infection in seropositive individuals who did not have a history of COVID-19 disease, positive PCR result and ARI symptoms on the day of examination. The maximum indicators of herd immunity were established in children 1–6 years old (31.1 %), 7–13 years old (37.7 %) and people over 70 years old (30.4 %). Differences in the level of seroprevalence in the age groups of 18–49 years are statistically significant. The highest level of seroprevalence was found among the unemployed (29.7 %), healthcare workers (27.1 %), education sector (26.4 %) and business sector personnel (25 %). In convalescents, COVID-19 antibodies are produced in 75 % of cases. In individuals with positive result of PCR analysis carried out earlier, antibodies are detected in 70 % of the cases. The results of the study of herd immunity to SARS-CoV-2 are essential to forecast the development of the epidemiological situation, as well as to plan measures for specific and non-specific prevention of COVID-19.

The first case of COVID-19 was registered in the Leningrad Region on March 13, 2020. The period of increasing intensity of the epidemic process lasted 8 weeks. One month after reaching the maximum incidence rate, a study was organized to determine seroprevalence to COVID-19 among the population of the Region.Objective of the study was to determine the level and structure of community immunity to SARS-CoV-2 virus in the population of the Leningrad Region in the period of intensive COVID-19 transmission.Materials and methods. The work was carried out within the framework of the Rospotrebnadzor project on assessment of community immunity to the SARS-CoV-2 virus in the population of the Russian Federation. The content of antibodies to SARS-CoV-2 was determined applying ELISA using a kit for the analysis of human serum or blood plasma for the presence of specific IgG to the nucleocapsid of the SARS-CoV-2 virus , manufactured by the State Scientific Center of Applied Microbiology and Biotechnology (Obolensk) in accordance with the instructions for use.Results and discussion. The study has showed that the herd immunity of the population of the Leningrad Region was 20.7 %. The maximum level has been established in children 1–6 years old (42.3 %) and people over 70 years old (29.0 %). The highest level of seropositivity, except for children and older people, was found among the unemployed (25.1 %). The lowest level of seroprevalence was detected in civil servants (12.8 %) and military personnel (16.7 %). It has been shown that the risk of infection increases by 1.5 times in case of contacts with COVID-19 patients. After exposure to COVID-19 virus, antibodies are produced in 82.1 % of the cases. In individuals with a positive PCR test result obtained earlier, antibodies are detected in 82.8 % of cases. The share of asymptomatic forms among seropositive residents of the Leningrad Region was 86.9 %. The results of assessing the herd immunity to SARS-CoV-2 in the population of the Leningrad Region indicate that during the period of intensive COVID-19 transmission, an average level of seroprevalence was formed. A significant proportion of asymptomatic forms of infection characterizes the high intensity of the latently developing epidemic process. The results obtained should be taken into account when organizing preventive measures, including vaccination, and predicting morbidity rates.

Currently, along with the increasing need of medical organizations for blood preparations, algorithms for laboratory testing of blood donors are not available for all infections with hemo-contact mechanism of transmission. A representative example is infection caused by parvovirus В19. Purpose of the study. The article presents the results of the original study, the purpose of which was to study the prevalence of antibodies to parvovirus B19 and the activity of the circulation of this virus in socially important categories of the population. Material and methods. The materials of the study were blood samples from blood donors of Saint Petersburg, as well as parvovirus В19 sequences isolated from DNA-positive plasma samples. Results and discussion. According to the results of the laboratory examination, a high proportion of carriers of virus-specific IgG antibodies was found in studied group of donors, which confirms the previous infection of parvovirus B19 in them and illustrates the high prevalence of infection in this socially significant group. Based on the results of the blood preparations testing, the presence of parvovirus DNA В19 in a significant number of samples was determined by polymerase chain reaction method. This indicates an current parvovirus infection in the examined donors and points to a high epidemiological risk of the blood products obtained from them. Sequencing and phylogenetic analysis of a fragment of the VP1 gene demonstrated that the studied isolates belonged to А1 genotype and its subtype 1А2, which correlates with the genotypes of parvovirus В19 circulating in the European Union and Asia. In addition, two previously unknown В19 parvovirus isolates were isolated, the nucleotide sequences of which were deposited into the international GenBank database. Conclusion. Based on the results of the study, it is justified to include testing of blood samples for markers of В19 parvovirus infection in existing algorithms of laboratory examination of donors, which will ensure prevention of hemo-contact infection of blood recipients with parvovirus В19.

Allergen-specific diagnostics is carried out on the basis of the data collection from the patient’s family and personal history, skin test results, provocative tests and laboratory research methods. Methods for determining specific IgE antibodies (sIgE) play a key role in confirming the diagnosis and identifying the pathogenetic mechanism of an immediate-type hypersensitivity to an allergen. The purpose of the study was to evaluate the results of determining sIgE for allergens of cat epithelium, house dust mite D. farinae and birch pollen in the blood serum of patients suffering from respiratory allergy, by comparing two methods of ImmunoCAP Phadia and 3gAllergy Immulite, as well as determining whether the results of these test systems are in concordance with the results of skin tests in the patients. The serum samples were obtained from patients of St. Petersburg adult outpatient clinics, who suffered from respiratory allergies (n = 50). The samples were analyzed in parallel in two laboratories, with each of the laboratories using single test systems. The retrospective skin test results were obtained from twenty six of the fifty selected patients. The inter-method comparison was conducted by determining the concordance of positive and negative results, correlation and regression analysis of sIgE results for each allergen and ROC-analysis to compare the diagnostic specificity and sensitivity of test systems in relation to the results of skin tests. This study showed that, in terms of agreement and contingency of the results, the Immulite test system had a close relationship with the Phadia test system. Both analysis of classes and quantitative sIgE analysis showed a good positive correlation from 0.79 to 0.99 (p < 0.0001) between the two test systems for all three allergens. High accuracy of coincidence in terms of sensitivity, area under the ROC curves (AUC) and cut-off threshold in both test systems was obtained for the D. farinae allergen. For allergens of cat epithelium and birch pollen, some differences between test systems were observed, i.e., sensitivity and AUC values were significantly higher in Immulite than in Phadia assay for both allergens.Thus, the inter-method comparison gave almost equivalent binary and quantitative results of the determination of sIgE antibodies to cat, tick and birch allergens. Comparison of in vitro test results, and their correlation with skin tests showed that the cat and birch in vitro antibody testing with Immulite assay was more closely connected with skin test results, than Phadia assay system.

Background. In the Russian Federation the number of a parvovirus В19 infection cases has increased significantly with the introduction of rubella into the measles elimination program and laboratory examination of patients with maculopapular rash and fever. The aim of study was the examination of the distribution of the parvovirus В19 infection in the North-Western Federal District. Materials and methods. In 2014–2017, 1044 blood sera of patients with exanthema diseases from different territories of the North-Western Federal District have been investigated with «Anti-Parvovirus B19 ELISA IgM» kit (EUROIMMUN, Germany) to detect IgM antibody, and 733 blood sera of clinically healthy men and women 18 to 60 years old have been tested for IgG antibodies using the «Anti-Parvovirus B19 ELISA IgG» kit (EUROIMMUN, Germany). Results. Parvovirus В19 infection is contentiously detected in 10 of the 11 territories of the district. Typical is the winterspring seasonality; in terms of the age structure – prevalence of children 3–6 (25,3% of cases) and 7–14 (33,3% of cases) years old was detected. A high proportion of seropositivity was established among the examined donors from the higher educational institutions of Saint Petersburg (75,4–88,9%%). Low rate of seropositivity (56,7%) was detected among pregnant women. A high proportion of false negative results in the primary diagnosis of parvovirus infection has been revealed. Conclusion. Parvovirus В19 infection is widespread in the territories of the North-Western of the Russia, mainly among children. The results indicate the feasibility of conducting a laboratory examination of pregnant women who are contact for exanthemous diseases, for markers of parvovirus infection; on the importance of screening donor blood for PV B19 DNA with “culling” pools characterized by high viral load; on the need for differential laboratory diagnosis between rubella and parvovirus infection.

Aim. Genotyping and molecular genetic characteristics of parvovirus B19, circulating in the NorthWest Federal District. Material and Methods. The material of the study is based on serum samples from 821 patients with maculopapular rash negative for antibodies IgM-measles and IgM-rubella were received at the St. Petersburg Regional Center for Measles and Rubella Surveillance in 2009-2017. In the present study we used genotyping by direct sequencing of the NS1/VP1 region of Parvovirus B19 genome. Results. DNA of the virus was detected in 59 (42.4%) of seropositive patients. To assess the heterogeneity of isolates, 14 samples were selected from patients from geographically remote regions of the NWFO, of different ages, regardless of gender, with a high viral load (106-107 copies/ml). Based on the phylogenetic analysis of the isolates showed that only the genotype 1A was detected in all isolates. The nucleotide sequences can be divided into two subgroups: 13 isolates (92.8%) belong to the subgroup 1A2, one isolate to the subgroup 1A1. Conclusion. The introduction of B19 screening from patients with fever / rash can provide meaningful information on the prevalence of parvovirus infection in the Russian Federation. Identifying new mutations of the virus and further analysis of their possible relationships with the course of the mutation disease can help in the development of medicines, as well as in the development of an effective vaccine against the parvovirus B19.

Parvovirus infection (PVI) is widespread in the world; more than 80% of the adult population have antibodies of IgG class to parvovirus B19. Malaria is a vector-borne parasitic disease caused by the protozoa of the genus Plasmodium, that is widespread in the countries of Africa, Southeast Asia, Oceania. The objective of the present study was to evaluate the effect of parvovirus B19 infection on the clinical course of malaria and the outcome of the underlying disease. During the period 2016–2018 blood plasma samples of 316 patients from the hospital of the Friya Prefecture of the Republic of Guinea (GR) with confirmed diagnosis of malaria were examined for the presence of PVB19 DNA. The clinical course of malaria in 316 examined patients was divided into group of either mild or complicated. In total, PVB19 DNA was detected in blood plasma in 55 of 316 patients (17.41±2.13%). But in the group with co-infection of PVB19 and P. falciparum complications were observed in 40 of 55 (72.73±2.75%) patients, and in 6 of 55 cases (10.91±4.40%) the disease resulted in death. In the group of patients with malaria without PVI, complications occurred in 99 of 261 patients (37.9±3.0%); of those 2 (0.77±0.54%) died. It was found that the most numerous group in the structure of malaria patients is represented by children under 5 (median 3) years (89, or 28.25±2.53%). Our results correlate with the data of other researchers who studied the PVI-associated malaria in children in malaria-endemic regions: among children under 5 years, the absolute majority of cases of PVI was accompanied by a complicated course of malaria. The primary parvovirus infection can aggravate the course of malaria, especially when combined with other unfavorable conditions (iron deficiency, malnutrition, helminthic infections, co-infections, etc.). Thus, infection with PVB19 becomes a critical factor, which can provoke a severe life-threatening anemia, and also cause other complications.

Wide migration processes typical for megacities, including St. Petersburg, require a comprehensive study of the infection among migrants arriving on a work visa. Biological material for research was taken from 370 migrants who arrived in St. Petersburg on a work visa. The control group is represented by 320 adults of St. Petersburg. The methodology of the study of the biological material depended on the type of pathogen and included classical and modern methods of research. All obtained data are processed using adequate methods of mathematical statistics. C. diphtheriae strains in migrant workers were isolated 80 times more often than in permanent residents of St. Petersburg. In St. Petersburg gravis biovar occurs in 25% of cases, in the visiting contingent — in 83% of cases, which is an unfavorable prognostic sign. In migrants 17% of C. diphtheriae strains have a “silent” gene (tox+), which, under known conditions, can resume toxin production. The local people are protected from diphtheria by 95%, and labor migrant is only 66%. 17% of migrant workers with C. diphtheriae strains have a low level of protection against diphtheria, which poses a threat to them and those in contact with them. Infection with brucellosis pathogens of labor migrants from Uzbekistan is 9 times higher than the local population, persons from Tajikistan — 60 times higher. The infection rate of migrant workers from Uzbekistan and Tajikistan C. burnetii is 25 times higher than that of the local population. The chronic course of these infections complicates diagnosis and reduces the quality of life. According to the results of the screening test, S. Typhi bacterium carrier is distributed 7 times more in migrant workers from Uzbekistan and 2 times more in persons from Tajikistan than among the local population of St. Petersburg. The seroprevalence of toxic H. pylori in migrant workers is 84%, which is much higher than that of permanent residents of St. Petersburg (57%). The causes of this phenomenon have not been studied and require further study. Labor migrants from Central Asia have a low level of population immunity to parvovirus infection: 37% of seropositive persons from Uzbekistan and 62% from Tajikistan compared with 78% of the local population. This may contribute to the spread of parvovirus infection involving infection of seronegative residents of St. Petersburg risk groups, including blood donors, pregnant women, persons with immunodeficiencies, hematologic and oncologic patients. The results obtained ascertain the tense epidemiological situation among labour migrants in St. Petersburg for a number of infections. Reliable information will help to organize the correct further study of the problem and conduct appropriate measures to preserve the health of the local population and the visiting contingent.

Parvovirus B19 (PV B19) replicates predominantly in progenitor cells of human erythrocytes and is transmitted by an airborne, vertical through and through blood or infected tissues. At-risk are pregnant women, people with immunodeficiency of different nature and individuals who need blood transfusions or organ transplantation. The available data indicate a high risk of infection through transfusion of blood containing the DNA of parvovirus B19, with viral load 105 copies/ml and above (Hourfar M.K. et al., 2011). According to the requirements of national regulations, the production of therapeutic drugs from plasma assumes the use of raw materials, free from viruses or with minimal viral load (Filatova E.C. et al., 2011). In some foreign countries a study of donor blood for the presence of DNA PV B19 is required; in our country the need for such screening is discussed (Giburt E.B. et al., 2013). Due to the fact that parvovirus is resistant to the methods of blood products desinfection, it is especially important to assess the quality of donor blood. Objective: To investigate the prevalence of the two markers parvovirus infection (IgG and PV B19 DNA) in blood samples from one of the blood centers at St. Petersburg. Plasma samples from 100 blood donors from Military Medical Academy blood centre were tested by ELISA for the presence of IgG antibodies of parvovirus B19. Positive samples were tested by PCR for the DNA of parvovirus B19. ELISA test system recomWell Parvovirus B19 IgG (Microgen GmbH, Germany) and diagnostic kits of Federal State Institution of Science «Central research Institute for epidemiology» of Rospotrebnadzor (Moscow, Russia) which are approved for use in RF was used according to the manufacturers instructions. It was shown that 78 out of 100 donors aged 18 to 58 years had IgG-antibodies.76 positive blood plasma samples were investigated by PCR, with the 19 donors have found DNA of parvovirus B19 (25%). Viral load of one donor was 106 copies/ml. In this case, there is the high risk of infection for the recipient. Results obtained are consistent with literature data. Obviously, it is need to investigate donor blood for parvovirus B19 presence. Obvious that quantification of the DNA of parvovirus B19 in blood products is need.