The review considers the relevant aspects of laboratory diagnosis of rabies. The methods of laboratory diagnostics of rabies infection, standardized by WHO in 2018, and their use in the Russian Federation are presented. The scheme of laboratory diagnostics of rabies, applied by specialists of the “48th CRI” of the Ministry of Defense of Russia, for the study of biological samples from deceased people is outlined. Between 2002 and 2018, the study of biomaterial was carried out using molecular-biological, virological methods of diagnosis and in some cases electron microscopy, which allowed to detect and identify the pathogen in 257 samples from 71 people, to certify and deposit new isolates of the rabies virus. Accumulation and analysis of the lessons learned in the application of molecular-biological method of rabies diagnosis allows us to recommend the use of RT-PCR, real-time RT-PCR sets (having a certificate of state registration) in healthcare and veterinary medicine practice to identify the causative agent of rabies infection. The use of molecular-biological methods is promising in terms of the development of rabies diagnosis to improve epidemiological surveillance and raise the efficiency of the biological protection of the population of the Russian Federation. 

The aim of the review was to consider the principles and criteria for the formation of funds of service microbiological collections and the specialized State collection of pathogenic bacteria (SCPB) at the RusRAPI “Microbe”. The rapid pace of characterization, study, and use of microbial diversity makes the development of criteria for the selection of microorganisms for permanent storage in collections particularly relevant. The number and format of these criteria are determined by the tasks the collection centers of different levels and specialization are facing. Service collections form their funds by depositing or acquiring type, reference, educational strains. In recent years, the practicability of expanding the range of strains, the deposition of which is desirable in service collections, has been recognized. These are strains characterized by phylogenetic, genomic, metabolic, ecological uniqueness; with a fully sequenced genome; known and emerging plant, animal and human pathogens that caused disease outbreaks; used in international research projects; having biotechnological and economic significance. The main task of the SCPB as a specialized state collection of pathogenic bacteria of groups I–II is to preserve strains characterizing the intraspecific diversity and populations of pathogens circulating in natural foci or in certain territories of the Russian Federation, isolated during epizootics, local or epidemic outbreaks. The selection criteria for strains for permanent storage are their ecological, phenotypic, and genetic peculiarities. The preservation of such a collection is important for future research using new technologies and tracking the evolution of pathogenic bacteria – causative agents of particularly dangerous infectious diseases. 

Yellow fever is an acute infectious disease of viral nature, the causative agent of which is vector-borne –is transmitted through the bites of infected mosquitoes. Massive epidemics caused by the yellow fever virus are observed in the countries of Africa, South and Central America annually. Imported cases are also registered in non-endemic territories. The review presents the currently available data on the distribution, structure and classification of the yellow fever virus, the identification of its genetic variants depending on the geographical distribution, as well as modern methods of detection and identification of the pathogen in samples taken from sick and dead people. It considers the possibility of using virological, immunoserological and molecular-genetic methods for the diagnosis of yellow fever in different periods from the onset of the disease and in retrospective studies. The lists of diagnostic drugs of domestic and foreign production for the detection of agent markers (antigen, RNA), as well as specific antibodies of IgM and IgG classes, approved for use on the territory of the Russian Federation, are provided. The relevance of further development, improvement and introduction into laboratory practice of reagent kits that allow to detect the yellow fever virus in samples from sick people in a short time, with high efficiency and specificity is demonstrated. This will help to establish a diagnosis promptly and conduct timely anti-epidemic measures, as well as to determine the level of the population stratum immune to the pathogen in endemic regions and evaluate the effectiveness of immunization for the vaccinated contingent. 

This review describes the current situation on highly pathogenic avian influenza virus in 2020 and provides forecast of the possible further spread of avian influenza in Russia. In 2020, the circulation of a wide variety of highly pathogenic avian influenza virus subtypes which have epizootiological and epidemiological significance was recorded in the world. Outbreaks of highly pathogenic avian influenza were reported in over 30 countries. Apart from this, human infections with influenza viruses of the A/H5Nx and A/H9N2 subtypes were reported. There was a large-scale epizootic in Russia in 2020, which affected more than 10 regions. Outbreaks among wild birds and poultry were caused by the highly pathogenic influenza virus A/H5N8 of clade 2.3.4.4b. As a result of those outbreaks, more than 1.5 mil. poultry were killed or perished. It was revealed that strains of the influenza virus isolated in Russia have a high degree of identity with the strains circulating in Europe and Southeast Asia. Thus, it was shown again that the territory of Russia plays an important role in the global spread of avian influenza virus. 

Analysis of the incidence of human brucellosis in the world in 2011–2020 is presented in the paper. An assessment of the epizootiological-epidemiological situation on brucellosis in the Russian Federation in 2020 is performed. It is outlined that the epidemiological situation on brucellosis in Russia over the past decade was characterized as unfavorable with downward trend in the incidence rate against the background of persistent epizootiological insecurity among cattle and small ruminants. Between 2011 and 2020, 3507 first identified human cases of brucellosis were registered. The long-term average number of cases is 350 per year, including 28 cases among children under 17 years old. The average long-term intensive morbidity rate per 100 000 people was 0.24, among children under 17 – 0.1. In 2020, 119 human cases of brucellosis were detected in Russia (0.08), which indicates that the trend towards an improvement in the epidemiological situation on brucellosis continues. The largest number of brucellosis cases among people was registered in the North-Caucasian (77.1 % of the total incidence across Russia) and the Southern Federal District (13.5 %). In the period of 2010–2020 (9 months), 4610 areas potentially hazardous as regards bovine brucellosis and 422 – as regards brucellosis in sheep and goats were registered in the Russian Federation. Analysis of the development of brucellosis situation in Russia indicates that in the medium term, with the current trend maintained, there is a real risk of widespread brucellosis distribution among farm animals in the constituent entities of the Central, Volga, Far Eastern and Siberian Federal Districts, as well as the persistence of epizootiological insecurity in the North Caucasus and Southern Federal Districts. Taking into account the current epizootiological-epidemiological situation and the long-term dynamics of the development in the Russian Federation, one can predict the incidence of brucellosis in people at a level below the longterm average values – 0.13–0.18 per 100000 of the population in 2021.

Objective was to analyze the epidemiological situation on Ixodidae tick-borne borreliosis (ITBB) in the constituent entities of the Russian Federation in the dynamics over the period of 2010–2020, taking into account the features of the year 2020, associated with the spread of COVID-19, and to forecast the development of the epidemic process for 2021. In 2020, 4180 cases of ITBB were registered in the Russian Federation, which is 1.93 times less than in 2019 and 1.73 times less than the long-term average annual figure for the previous 10 years. A significant decrease was noted in all federal districts (FD), with the exception of the Central FD, where more than half of all cases occurred. Compared to 2019, 75 out of 78 subjects experienced a decrease in the incidence rate in 2020, while in 56 entities that decrease was statistically significant. The multiplicity of the decrease in the incidence of ITBB in 2020 for all FD was significantly greater than the multiplicity of the decrease in the frequency of contacts of the population with ticks. Infection of Ixodidae ticks of various species with borrelia in natural foci in 2020 was statistically significantly higher than in 2019. Probably, the decrease in the registered incidence of ITBB against the background of the COVID-19 pandemic is due not only to a decrease in the intensity of contacts of the population with natural foci, but also to a sharp redistribution of the volume of inpatient and outpatient medical care in favor of COVID-19 patients. Given the high degree of significance of the identified trends in the dynamics of the epidemic ITBB process during 2010–2020, there is reason to expect an increase in the incidence in the Bryansk, Voronezh, Ryazan, Tula and Saratov regions in 2021, which requires special attention in terms of strengthening preventive measures and monitoring of the activity and structure of natural foci. In the rest of the entities of the Russian Federation, provided that the volumes of preventive measures are maintained on the same level and in the absence of abnormal natural and climatic phenomena, preservation or a slight reduction in the incidence of ITBB is likely to occur in the short term. At the same time, despite the tense situation regarding the new coronavirus infection, there is an obvious need to draw close attention to the problems of diagnosis and prevention of natural focal infections.

The review used the data from operational monitoring carried out by the Reference Center for Monitoring over HFRS – “Kazan Research Institute of Epidemiology and Microbiology of the Rospotrebnadzor”, based on official data provided by the Rospotrebnadzor institutions in the constituent entities of the Russian Federation. Statistical processing was conducted using conventional methods of variation statistics applying the Excel program. Over the past decades, hantavirus diseases have become very relevant and spread throughout the world. In the territory of the Russian Federation, natural foci of HFRS are located in the European part of the country, Western Siberia and Far East. The most epidemically active foci are situated in the European part of Russia. Over the past decade, the intensive incidence rate of HFRS in the Russian Federation stayed within the range of 3.0–9.5 per 100 thousand of the population, the long-term average annual indicator – 5.2 per 100 thousand of the population. In 2020, 3845 cases of HFRS were registered (2.62 per 100,000 of the population). There was a decrease in the incidence of HFRS by 3.6 times, compared with the indicators of 2019. A factor that may have influenced the decrease in the incidence of HFRS was the depression of the epizootic process among small mammals, the main carriers of HFRS pathogens, due to natural and climatic factors. The nature of the distribution of HFRS incidence across the territory of the Russian Federation in 2020 was heterogeneous. Statistical processing of the data made it possible to identify 5 groups of territories that differ in the level of HFRS incidence. Almost all constituent entities of the Volga Federal District and the Kostroma Region belonging to the Central Federal District were classified as groups of territories with high and very high incidence rates. In 2021, the deterioration of the epidemiological situation is predicted in the summer-autumn period of the year in the Volga Federal District and four entities of the Central Federal District. 

The aim of the study was to clarify the boundaries of the Central Asian natural plague focus of Kazakhstan and the modern boundaries of the areal of the great gerbil (Rhombomys opimus) in order to improve epizootiological monitoring and increase the effectiveness of preventive (anti-epidemic) measures.

Materials and methods. Data from the epizootiological monitoring of the great gerbil populations in 14 autonomous foci of the Central Asian desert natural plague focus in the Republic of Kazakhstan between 2010 and 2020 were used for the analysis. An epizootiologic survey of an area of 875350 km2 was carried out. When processing the data, epidemiological, epizootiological, statistical research methods, as well as GIS technologies were used.

Results and discussion. An increase in the total area of the Central Asian desert natural plague focus of the Republic of Kazakhstan by 79710 km2 (9.98 %) has been established for the period of 1990–2020. It is noted that the change in the area of plague-enzootic territory was a consequence of the ever changing areal of the main carrier of plague pathogen – the great gerbil – under the influence of climatic and anthropogenic factors. The most significant changes were found in the southeastern part of the plague-enzootic territory, including those for the Betpakdala (50 %), Balkhash (34.3 %), Taukum (13.3 %) and Mojynkum (0.32 %) autonomous foci. The area of the Aryskum-Dariyalyktakyr autonomous focus decreased by 2100 km2 (4 %). In 2000–2002, new Alakol’sky and Ili intermountain autonomous foci with a total area of 26759 km2 were discovered. It is shown that due to the regression of the Aral Sea, the areal of the great girbil expanded and the area of the North Aral and Kyzylkum natural plague foci increased by 10500 km2 (29.2 %) and 560 km2 (0.4%), respectively. The areas of the Aral-Karakum and UralEmba desert autonomous foci, on the contrary, decreased by 2000 km2 (2.6 %) and 12300 km2 (17.6 %), respectively. Passportization and landscape-epizootiologic zoning of the territory of the Central Asian desert natural plague focus of the Republic of Kazakhstan has been completed. 

The aim of the work was to design and carry out experimental studies of a set of reagents to identify the spectrum of genes that determine the resistance of the Vibrio cholerae strains to antibacterial drugs.

Materials and methods. V. cholerae strains isolated from humans and environmental objects during epidemiological complications and the cholera-free period were included in the study. Sensitivity to antimicrobial drugs was evaluated by the disk diffusion method. Whole genome sequencing was performed on an Illumina MiSeq. The profile of resistance genes was determined based on a comparison with the ResFinder database. The temperature regime, the composition of the reaction mixtures, and the reaction parameters were optimized; the specificity, sensitivity and reproducibility of the constructed prototype test system were measured.

Results and discussion. The spectrum of antibiotic resistance and the profile of resistance genes were determined for the studied strains. To develop multiplex PCR, we selected the most common in the V. cholerae populations genes, which are responsible for resistance to tetracycline (tetA), streptomycin (strA), florfenicol/ chloramphenicol (floR) and trimethoprim/sulfamethoxazole (two variants of the dihydrofolate reductase gene: dfrA1 and dhfR), as well as SXT element integrase gene (int). In the reaction, markers were specifically detected in accordance with the genomic resistance profile, which correlates with the phenotypic manifestation of resistance determined by the disco-diffusion method. The sensitivity of the developed panel of primers and probes for V. cholerae strains was 103 –104 CFU/ml. Therefore, taking into account the specificity, rapidity and simplicity of the reaction, the developed system of primers and probes can be successfully applied for a preliminary assessment of the resistance of the V. cholerae strains to antimicrobial agents. 

The aim of the study was to characterize and carry out molecular-genetic identification of Yersinia pseudotuberculosis strains isolated in the Sarydzhaz high-mountain focus of the Tien-Shan.

Materials and methods. The Y. pestis and Y. pseudotuberculosis cultures were differentiated according to their sensitivity to diagnostic bacteriophages, motility, urea fermentation, and pesticin production. Whole genome sequencing was performed using the Ion S5 XL System (Thermo Fischer Scientific). Ion Torrent Suite software package, 5.12 and Newbler gsAssembler 2.6 were used for data processing and de novo assembly of raw read sequences. The dendrogram was constructed using the Maximum Likelihood method applying the PhyML 3.1 software.

Results and discussion. Strains of Y. pseudotuberculosis were isolated from museum mixed with Y. pestis cultures obtained from marmots in the Sarydzhaz high-mountain focus. According to whole genome SNP analysis, they belong to the phylogenetic group O:3 serovar, which is widespread throughout the world. Y. pseudotuberculosis is often present in mixed with Y. pestis cultures, isolated from rodents, which should be taken into account when carrying out laboratory diagnostics of plague in natural foci. 

Objective of the study was the development of experimental ELISA tests and lateral flow immunoassays for detection of staphylococcal enterotoxins, A and B types.

Materials and methods. Hybridomas, producing monoclonal antibodies against staphylococcal enterotoxins A and B from State Collection of the Affiliated Branch of the “48th Central Research Institute” of the Ministry of Defense of the Russian Federation, BALB/c mice and staphylococcal enterotoxins A and B were used in the research. Hybridoma cells were incubated in culture flasks and in the peritoneal cavity of BALB/c mice. Monoclonal antibodies were isolated from ascitic fluids through precipitation with saturated ammonium sulfate subsequently purified using ion-exchange chromatography. Obtained preparations of monoclonal antibodies were used for the construction of ELISA tests and immune-chromatographic reagent panels for the detection of staphylococcal enterotoxins A and B. Specific components of ELISA tests were lyophilized in protective media.

Results and discussion. ELISA tests and lateral flow immunoassays which allow for detecting staphylococcal enterotoxins A and B at concentrations of 0.5 ng/ml and higher, including in food samples, have been constructed. 

The aim of the study was to improve monitoring of natural foci of rabies based on the use of modern technologies of cartographic analysis.

Materials and methods. A retrospective study was carried out on the data of official registration of rabies in the Trans-Baikal Territory (Eastern Trans-Baikal Region) for 1950–2020. The spatial spread of rabies among animals was compared for two time periods: 1972–1978 (n=157 cases) and 2014–2020 (n=61 cases). Software packages QGIS 3.16.0, ArcMap 10.8.1, ArcScene 10.8.1 and electronic landscape-geographical maps of the world “Natural Earth”, “OpenStreetMap” were used for the mapping. Analyzed territorial units (ATUs) tied to a degree grid (0,5º × 0,5º) were marked on the cartograms. The interdependence between the localization of rabies cases and landscape elements was assessed statistically, comparing between the rabies free and the rabies affected ATUs.

Results and discussion. Differences in the landscape confinedness of rabies epizootics in Eastern Trans-Baikal Region at different periods of time have been established. Until 1983, dog rabies prevailed, and epizootics spread beyond the forest-steppe zone. In 1984–2013 rabies among animals was not recorded. In 2014–2020 red foxes (Vulpes vulpes) were the main source of the rabies virus. The area of the epizootic has more than halved in comparison with 1972–1978. The main manifestations of rabies were observed at the junction of lowland and mountainous, steppe and forest areas. The rabies affected ATUs were characterized by more pronounced landscape variables. Possible routes of cross-border spread of the rabies virus have been identified. The connection between the features of the spatiotemporal spread of rabies and genetic variants of the virus, climate change, animal migrations and anthropogenic factors in Eastern Trans-Baikal Region in 1950–2020 is discussed. The results of the study are proposed to be used to adjust the programs for barrier oral vaccination of the foxes. 

The aim of this study was to determine the dynamics of the residual infectious activity of the SARSCoV-2 virus on various types of surfaces, including banknotes and coins, in samples of drinking dechlorinated water and samples imitating seawater, with a concentration of sodium chloride salts of 0.9 and 3.5 % at a temperature of 24–28 ºC.

Materials and methods. The studies were carried out using the SARS-CoV-2 coronavirus strain nCoV/Victoria/1/2020, from the collection of the SSC VB “Vector”, the initial titer being (6.0±0.2) lg TCD50/ml. We used a Vero E6 cell culture from the collection of the SSC VB “Vector” in the form of a 2-day monolayer with a confluence of 95–100 %, grown in 96-well culture plates.

Results and conclusions. The SARS-CoV-2 coronavirus is viable in both fresh and sea water, regardless of its salinity, for at least 48 hours, and the degree of preservation of the residual infectious activity of the virus depends on the water temperature: the lower it is, the better the virus is preserved. It was found that at a temperature of 24–28 C, the SARS-CoV-2 coronavirus is able to maintain infectious activity on all types of test surfaces studied for at least 48 hours, while the degree of the residual infectious activity of the virus depends on the type of surface. The virus is best preserved on stainless steel, plastic and glass. It is demonstrated that SARS-CoV-2 virus activity is retained on the surface of paper money and coins for longer than 24 hours. The conducted studies have confirmed the ability of the SARS-CoV-2 coronavirus to maintain its infectious activity in the environment under favorable conditions and, accordingly, to pose an epidemiological threat to the population. 

The aim of the study was a comprehensive analysis of the phenotypic and genetic properties of Yersinia pestis strains isolated in the Sarydzhaz and Upper-Naryn high-mountain foci of the Tien Shan in 2019–2020; determination of the present-day population structure and areal of these highly virulent strains of the plague pathogen.

Materials and methods. Studies of biochemical properties (fermentation of carbohydrates, nutritional requirements), virulence (in vitro and in laboratory animals), molecular-genetic analysis and whole genome sequencing of Y. pestis strains isolated in the Sarydzhaz and Upper-Naryn high-mountain foci in 2019–2020 have been carried out. We used Y. pestis strains from the foci of the Tien Shan and Pamir-Alai dated 1928–2016 for the comparison. Whole genome sequencing was performed using the Ion S5 XL System. Phylogenetic analysis was performed on the basis of 1443 identified core SNPs in 36 Y. pestis strains of various phylogenetic lines included in the analysis. The construction of dendrograms was carried out using the Maximum Likelihood algorithm, PHYML program, HKY85 model.

Results and discussion. It is established that all Y. pestis strains isolated in the Sarydzhaz and Upper-Naryn high-mountain foci in 2019–2020 belong to the 0.ANT5 phylogenetic branch of the ancient biovar of the main subspecies. Genome-wide sequencing revealed the presence of two 0.ANT5 clones, the first of which consists of strains from the basin of the river Kooylu in the Sarydzhaz focus, dated 2020. The second powerful clone includes the strains of 2012–2020 isolated in the Sarydzhaz and Upper-Naryn foci. The high virulence of the isolated strains has been shown. It was concluded that further study of the territories of the highmountain foci of the Tien Shan and Pamir-Alai is necessary to establish the current boundaries of the 0.ANT5 areal, as well as to identify the circulation areas of Y. pestis of other phylogenetic lineages. 

The aim was to study SARS-CoV-2 immunity among medical workers in Kazan.

Materials and methods. Studied were serum samples from 348 medical workers from 10 medical organizations in Kazan, divided into groups according to the level of the alleged risk of infection of employees. To determine IgG, a two-stage direct version of the solid-phase ELISA and the test-system “SARS-CoV-2-IgG-ELISA-BEST” (Russia) were used.

Results and discussion. At the time of the study and over the previous three months, the examined medical workers had no symptoms of acute respiratory viral infection or respiratory tract infections; there were negative results of examining nasopharyngeal/ oropharyngeal swabs for the presence of SARS-CoV-2 RNA. Seroprevalence for IgG to SARS-CoV-2 virus for different medical organizations in Kazan ranged within the scope of 3.3–30.8 % and averaged 16.4 %. The wide variation in seroprevalence values in medical workers of different medical organizations may indicate different levels of intensity of professional contacts and the effectiveness of anti-epidemic measures in these medical organizations. Among medical workers with seropositive results, the prevalence of persons with a very high coefficient of positivity (49.1 %) is observed, which characterizes high level of antiviral antibodies. The presence of a high proportion of seropositive individuals among medical workers, who have had an asymptomatic form of COVID-19 confirms the high intensity of the latent epidemic process, which must be taken into account when organizing preventive measures, including vaccination. 

The aim of the work was to rank statistical models for assessing the contribution of a number of factors that determine the epizootic situation on natural-focal infectious diseases in the communities of non-synanthropic small mammals (SM) in the forests of Ekaterinburg.

Materials and methods. The SM survey was carried out for three years in the summer-autumn period. The animals were caught with snap tpaps on a standard bread bait, 9705 trap-nights were worked out. To identify infections (hemorrhagic fever with renal syndrome, tularemia, leptospirosis, yersiniosis, pseudotuberculosis), 333 SM specimens (rodents and shrews of six species) were used, randomly taken from the general sample. To determine the pathogens, the methods of enzyme immunoassay and polymerase chain reaction were used. The cumulative infection rate of small mammals with all studied natural-focal infections was evaluated. Statistical data processing was carried out from the standpoint of a multi-model approach. The selection of models was performed using the Akaike information criterion with the calculation of the sum of the weights of the models based on their full spectrum (SW).

Results and discussion. Carriers of all of the mentioned above infections, except for pseudotuberculosis, have been identified in the forest parks of Ekaterinburg. According to the ranking, the model with three predictors received the highest weight: species, year, and the abundance of SM of the previous year in a particular habitat. The most significant predictors for the full spectrum of models are the year (SW=1), species (SW=0.6), abundance of animals in the current and previous year (SW=0.48). The distribution of positive samples by species of small mammals corresponded to their ranking by abundance in the community. The influence of the factors “season” (summer or autumn) and “area” (place of capture of animals) turned out to be insignificant on the scale of the studies (SW = 0.3 and 0.16, respectively). The percentage of infected samples in total for all infections varied significantly by location and year (0–60%). The possible significance of unaccounted factors is discussed: landscape features and the mode of using forest parks, dispersal of small mammals. The conclusion is made about the usefulness of the multi-model approach in the analysis of the data from epizootiological studies. 

The aim of the work was to study the genetic diversity and spatial-temporal genotype structure of Yersinia pestis subspecies central asiatica biovar altaica in the Gorno-Altai natural plague focus, using MLVA25-typing.

Materials and methods. MLVA25-typing of 330 strains of Y. pestis ssp. central asiatica bv. altaica, isolated in the Gorno-Altai mountain natural plague focus during 1961–2015 was carried out. The phylogenetic tree was constructed with the help of UPGMA and MST algorithms.

Results and discussion. The analyzed strains have been differentiated into 34 MLVA types based on cluster analysis. The formed major groups of strains show pronounced spatial confinedness. Three chorological groupings of the plague agent with peculiar genotype characteristics have been identified. Each of the groupings is circulating among the main carrier (Ochotona pallasi) population and within the limits of the similarly-named mesofocus, respectively (Ulandryksky, Tarkhatynsky and Kuraisky). MLVA25 structure of Y. pestis in Ulandryksky and Kuraisky mezofoci show stability over time; there are no significant changes from the time of their first detection in 1961 and 1999, respectively. The dramatic changes in MLVA25 structure are observed in Tarkhatynsky mesofocus, which is known from 1972. Mass expanding of the MLVA25 types which were very rare before took place there from the beginning of 1990-s, along with elimination of the types absolutely dominant up to 1980s. Most likely the changing of dominating genotypes is attributable to the bottleneck effect, arising from the sharp decline of the focal epizootic activity in the mid 1980s. 

The aim was to carry out a comparative analysis of the immunogenic activity of the live plague vaccine obtained on various nutrient media.

Materials and methods. The subject of the study was the blood of outbred white mice immunized with a series of live plague vaccine based on Yersinia pestis EV NIIEG strain, produced using experimental and regulated nutrient media. The immunogenic activity of vaccines was studied through flow cytometry. The intensity of antigen-reactivity of lymphocytes was determined in cell tests in vitro, analyzing the early activation marker CD25+ . For the specific activation of lymphocytes, a complex of water-soluble antigens of the plague microbe was used. To identify the interdependence between the presence of protective anti-plague immunity and the level of CD 25+ expression intensity, the ED50 of the series under study was determined by the standard method.

Results and discussion. A comparative analysis of the immunogenic activity of the live plague vaccine obtained on the experimental nutrient medium with the vaccine produced on Hottinger’s agar has been performed. When animals were immunized with doses of 4·103 , 2·104 and 1·105 live microbial cells (regulated doses), the highest level of expression of CD25 marker by lymphocytes was on the day 14, with a subsequent decrease on the day 21 after vaccination. When determining immunogenicity using the conventional method, a high degree of direct correlation between the number of surviving animals and an increase in the level of lymphocytes expressing markers of early activation has been established. Comparison has revealed the general pattern: when the lowest immunizing dose (8·102 ) was administered, activation of early immunity markers was not observed. In case of immunization with higher doses on days 7, 14 and 21, a proportional increase in the number of CD25-positive lymphocytes after stimulation with a specific antigen under in vitro conditions is detected in the blood of biomodels.