Vaccine strains Yersinia pestis EV NIIEG at a dose of 103 CFU and Francisella tularensis 15 NIIEG at a dose of 102 CFU induced changes in the concentration of cyclic nucleotides in the thymus and spleen of white mice. Antigen-induced changes in the cAMP/cGMP ratio in immunocompetent organs had a phase or oscillatory character, which seems to be related to the regulation of postvaccination immunoreactivity in the body. Synthetic organoselenium compound 974zh stimulated an increase in the amplitude of cAMP/cGMP oscillations, indicating its stimulating effect on the immunogenic properties of vaccine strains at doses an order of magnitude below the standard doses.

Relevance. The new coronavirus infection (COVID-19) is still a public health problem and a threat to socio-economic well-being. Most studies have focused predominantly on humoral immunity, and there are no data on the cellular composition of blood in dynamics. Aim. To study the dynamics of changes in blood cellular composition depending on the type of immunity formed (natural, hybrid, breakthrough, postvaccinal) to SARS-CoV-2 virus. Materials and Methods. A total of 130 volunteers participated in the study. Immunophenotyping of peripheral blood leukocytes using flow cytometry was performed. The presence of specific IgG antibodies to N-protein SARS-CoV-2, total IgA and cytokines (IL-4, IL-10, IFN-γ, TNF-α) was assessed in serum by ELISA. Results and Discussion. A statistically significant increase in BL was recorded in volunteers with hybrid immunity 1 month (14,0% (12,3–16,4%)) after vaccination compared to healthy volunteers (9,1% (6,4–10,2%), p = 0,0007) and people with primary COVID-19 infection (10,2% (8,3–12,1%), p = 0,0134). In volunteers with natural and hybrid immunity, as well as in revaccinated people, an increase in B1-cells (CD3-CD19+CD5+CD27-) was observed during 3–9 months of observation. It is shown that the increase of B-lymphocytes with «switched» class of synthesized antibodies was detected in people with breakthrough immunity. Increased levels of T-lymphocytes expressing HLA-DR were recorded in all individuals during 6–9 months of follow-up. Volunteers with breakthrough immunity showed a significant increase in the positivity index when assessing the presence of specific IgG class antibodies to the coronavirus N-protein compared with volunteers with natural and hybrid immunity. Conclusions. Vaccination promotes protective immunity sufficient for timely activation of memory T- and B-cells in breakthrough immunity and maintenance of immunologic efficacy in hybrid immunity against COVID-19. The results help to assess the strain of innate and adaptive immunity in novel coronavirus infection and to fill gaps in the understanding of immunopathogenesis in COVID-19.

Collecting of hard ticks by a flag from vegetation in Askold Island (Primorsky Territory) in May 17, 2023 has revealed the following 3 species: Haemaphysalis longicornis Neumann, 1901 (809 specimens), Haemaphysalis japonica douglasi Nuttall et Warburton, 1915 (223), Ixodes persulcatus Schulze, 1930 (4). A total of 1036 tick specimens were collected. The territory of the western part of the island was surveyed: a broad-leaved maple forest (925 ticks were collected) and a large-grass meadow (111). Identification of tick species was carried out according to morphological characters. The hard tick fauna of Askold Island is characterized by: 1) the dominance of H. longicornis, which is absent on neighboring islands; 2) a high proportion of nymphs in May among representatives of the genus Haemaphysalis (H. longicornis 96.0%, H. japonica 25.1%), the peak abundance of which is common in July–August; 3) a high abundance of ticks (more than 90.0 individuals per flag-hour; 4) absence of males in H. longicornis (32 females were collected). PCR did not detect infection of 160 nymphs (pools of 20 individuals) H. longicornis with markers of nucleic acids of tick-borne encephalitis virus, borrelia, anaplasma, ehrlichia and West Nile fever. However, since representatives of the genus Haemaphysalis are known as carriers of many other pathogens, the high abundance of hard ticks and the incompleteness of data on their infection rate do not allow us to classify the territory of Askold Island as an epidemiologically low-risk territory.

Recently, pathogenic Leptospira culture isolation is an extremely rare phenomenon in Russia.The aim of our work was to synthesize the lessons learned at the Irkutsk Anti-Plague Institute from Leptospira culture isolation and identification since 2011.Materials and methods. Material from eight individuals with suspected leptospirosis and from 942 small mammals (SM) was examined using PCR and microscopic agglutination test (MAT), from humans and 260 SM, applying bacteriological method. Bacteriological temperature test, MAT, PCR, MLST and MALDI-TOF mass spectrometry with the original Leptospira protein profiles base were used to identify cultures. Six complete genomes were generated at the Central Research Institute of Epidemiology of the Rospotrebnadzor.Results and discussion. Leptospira have not been isolated from humans against the background of taking antibiotics, despite the positive PCR and MAT results. Four cultures of Leptospira borgpetersenii of the Javanica serogroup and three L. kirschneri (Grippotyphosa) have been isolated from SM. The results of identification using MLST scheme No. 1 and MALDI-TOF MS are identical. MLST in silico has shown the uniformity of two Grippotyphosa serogroup strains from Primorie and Khabarovsk with a sequence-type (ST) profile 110:100:94. ST146 is determined in four Javanica serogroup strains according to scheme No. 1, and unique single nucleotide polymorphisms are detected according to schemes No. 2–3. Thus, in Siberia and the Far East, between 2012 and 2016, seven pathogenic Leptospira cultures were isolated from carriers in natural foci; carrier infection rate being12.0–48.9 %. Javanica serogroup strains differ in the MLST profile characteristics and adapt to nutrient media for a longer time than Grippotyphosa serogroup strains.

One of the important directions for increasing the immunogenic properties of vaccine strains against highly dangerous infections is the search for adjuvants that not only stimulate the immunological effectiveness of vaccination, but can also provide a metabolic correction of the vaccination process. Organoselenium compounds have immunotropic properties and an antioxidant effect, and therefore, the study of the effect of the organoselenium compound 2,6-dipyridinium-9-selenabicyclo[3.3.1]nonane dibromide (974zh) on the activity of the TLR2 and TLR4 gene expression by macroorganism cells of experimental animals immunized with Yersinia pestis EV NIIEG vaccine strain, is a current area of research.The aim of the work. To assess the TLR2 and TLR4 gene expression by cells of the immune phagocyte system of experimental animals immunized with the Y. pestis EV vaccine strain against the background of immunomodulation with the organoselenium compound 974zh.Materials and methods. The study was carried out on 125 certified outbred white mice. Biological material (blood, spleen) was disinfected, and the spleen was homogenized. RNA isolation and reverse transcription were performed using commercial reagent kits. The expression level of the TLR2 and TLR4 genes was determined using real-time polymerase chain reaction with specific primers.Results. When assessing innate immunity using the example of blood and spleen cells of animal models, features of the TLR2 and TLR4 gene expression were revealed in response to the introduction of the Y. pestis EV vaccine strain against the background of immunomodulation with the 974zh. It was found that 974zh induces a statistically significant increase in TLR2 gene expression when co-administered with Y. pestis EV at a dose of both 104 CFU and 103 CFU.Conclusion. Y. pestis EV against the background of immunomodulation with 974zh, stimulates the expression of the TLR2 and TLR4 genes, which may indicate an increase in the immunogenic properties of the Y. pestis EV vaccine strain under the influence of this preparation.

Anthrax remains relevant in the world and in the Russian Federation. In Siberia and the Far East, epizootological, epidemiological, environmental and microbiological monitoring of anthrax is constantly carried out. To analyze the epizootological and epidemiological situation of anthrax, we used the information from veterinary institutions and Rospotrebnadzor for 24 regions, as well as reference and archive materials. On the territory of Siberia and the Far East for the period from 1985 to 2023, pronounced epizootological and epidemiological problems of anthrax are observed in the Yamalo-Nenets Autonomous Okrug, the Republic of Buryatia, Omsk Region and the Altai Territory. Over the last five-year observation period, high epizootic activity has been observed in the west of the Republic of Tyva. A total of 3,375 livestock animals and 128 people fell ill. The anthrax database contains information on 7,491 stationary anthrax-infected points in 22 subjects and 562 anthrax burials and cattle burials in 17 subjects of Siberia and the Far East. B. anthracis strains have slight variability in biological properties and belong to two global genetic lines – A and B. In order to prevent anthrax, it is necessary to ensure surveillance of soil foci of anthrax (anthrax burials and cattle burials, “plague fields”), a high level of livestock animals registration and their specific vaccination coverage; to control the implementation of veterinary and sanitary requirements for pre-mortem inspection and emergency slaughter of livestock, the sale of meat and meat products, and biological waste disposal; to carry out explanatory work among the population.

The polymorphism of HLA class II genes was studied in COVID-19 survivors and vaccinated people. Six allelic variants of DQA1, 10 of DQB1, and 11 of DRB1 were identified. The DQA1*05:01 allele predominated in vaccinated volunteers and the DQA1*02:01, *01:03, and DQB1*06:02-8 alleles predominated in convalescents. In the groups with DQA1*01:01, *05:01 and *06:01 alleles, a high proportion of individuals seropositive for SARS-CoV-2 S protein was found. In the group with DQA1*02:01 allele, 40% of volunteers were found to have IgM and a significantly lower quantity of IgG to N protein of coronavirus. Comparative analysis showed a statistically significant increase in IL-10 levels in carriers of the DQA1*01:01 allele, which may indicate the influence of this allele on cytokine production. Further study of the immune response indices and their association with HLA class II gene polymorphism will provide better understanding of the mechanisms of COVID-19 immunogenesis.

The aim of the review was to conduct a comparative analysis of the epidemiological situation on tick-borne encephalitis (TBE) over 2014–2023 in the constituent entities of the Russian Federation located in the European and Asian parts of the country and to give a forecast of incidence for 2024. The incidence of TBE in 2023 only marginally decreased as compared to the peak values in 2022, which leveled down the ten-year trend towards reduction. Grouping of the entities of the Russian Federation according to the average incidence of TBE over a decade made it possible to classify 17 of them as regions of low, 15 – of medium, and 17 – of high epidemiological risk. In general, the epidemiological situation regarding TBE is more unfavorable in the Asian part of the country. A list of species of Ixodidae ticks, the main vectors of the tick-borne encephalitis virus, is provided, as well as subtypes and genetic variants of the latter, identified in the European and Asian parts of the country. The peculiarities of the epidemiological situation on TBE and the scope of preventive measures undertaken in Russia in 2023 are considered. It is shown that there are no clearly outlined trends in the nature of changes in the incidence of TBE in endemic federal districts and entities of the country, and the expected incidence rates in 2024 will remain at the long-term average level.

The aim was to determine the phylogenetic position and features of the genome organization of individual groups of Vibrio cholerae strains isolated in Siberia and the Far East under different epidemiological situations during the seventh cholera pandemic.Materials and methods. We examined 275 V. cholerae strains, isolated during epidemic complications and during the cholera-free period in Siberia and the Far East, with different profiles of the main genomic loci of pathogenicity. The genomes of 969 V. cholerae strains from GenBank were used for phylogenetic analysis. The phylogeny reconstruction was carried out through calculating the distances between strains based on the occurrence of k-mers. The search, analysis and visualization of the loci structure in mobile genetic elements in V. cholerae genomes were performed using the blastn and Prokka programs and the author’s R and Python scripts.Results and discussion. Strains of V. cholerae isolated in Siberia and the Far East have been included in three global phylogenetic lines – L2, L3, L4. The distribution of strains from Siberia and the Far East along phylogenetic lines corresponds to the epidemiological situation in which they were isolated. We have identified the differentiation of strains by groups consistent with the global waves of spread of the etiological agent of the seventh cholera pandemic. We also traced potential paths for the import of the cholera pathogen into the territory of the Russian Federation. It has been revealed that spontaneous mutants that lost cholera toxin genes during storage and cultivation on nutrient media belong to the L2 phylogenetic lineage as well as toxigenic El Tor vibrios. The structural analysis confirms the differences in their genome organization and strains that do not have a CTX prophage during primary PCR screening. We recommend a two-stage algorithm of phylogenetic analysis within the framework of genomic monitoring of cholera agent: the first stage is a simplified assessment based on the occurrence of k-mers for express epidemiological analysis; the second stage is an in-depth analysis of genomes using a complex of phylogenetic methods for the reconstruction of links in individual epidemic complications, to establish patterns of origin and time of divergence of the pathogen clones.

The aim of the review was to assess the epidemiological situation in natural plague foci in the Russian Federation, near and far abroad countries in 2023 and to forecast their epizootic activity for 2024. In 2023, cases of plague were registered in five countries worldwide: the Democratic Republic of the Congo (60 cases), the Republic of Madagascar (14), the United States of America (2), the People’s Republic of China (3), and Mongolia (5). A total of 84 cases of plague were recorded, of which 22 (26.2 %) were fatal. In the Russian Federation, in 2023, epidemic risks in epizootically active natural foci were significantly reduced due to the implementation of a set of preventive measures carried out by Rospotrebnadzor institutions, which was the guarantor of ensuring epidemiological well-being as regards plague. Plague epizootics were detected on the territory of two (Gorno-Altai high-mountain and Tuva mountain) out of 11 natural plague foci in the Russian Federation in 2023. Epizootics were reported on the territory of the Kosh-Agach district of the Altai Republic and the Mongun-Taiginsky kozhuun of the Tuva Republic. The total area of epizootics was 731.2 km2 (in 2022 – 248.3 km2). In total, 55 cultures of the antique biovar of the main subspecies Yersinia pestis pestis were isolated in 2023 (19 in 2022). The forecast for continuation of the tense epidemiological situation in the territory of the Altai and Tuva Republics in 2024 is substantiated. The trend of sustained growth in the epizootic potential of the East Caucasus high-mountain and Dagestan plain-piedmont plague foci is outlined. The prospects for introducing an automated electronic system for assessing the epidemic potential of natural plague foci into practice are explained.

Entomoparasitic nematodes have a specific role to play in the persistence of Yersinia pestis in natural foci, however their natural microbial environment has not been studied.The aim of the study was to search for bacteria associated with nematodes parasitizing fleas-vectors of plague in the Tuva natural focus.Materials and methods. Fleas were collected during the planned epizootiological surveillance in May, 2017 and 2018. During the taxonomic identification of insects, the presence of parasitic nematodes was recorded. In 2017, bacteriological examination of fleas affected by nematodes and those free from them was carried out separately without dissection. The presence and number of bacteria colonies on the agar plates were taken into account. The results were evaluated by conventional methods using the Excel program. The t-criterion, one-factor analysis of variance were employed. In 2018, 84 invaded fleas were dissected. Extracted nematodes were suspended in Hottinger’s broth, followed by cultivation of grown bacteria on Hottinger’s agar. Systematic position of isolated cultures was determined through mass spectrometric analysis (MALDI-TOF) and partial sequencing of 16S rRNA.Results and discussion. In 2017, 30 samples of fleas with helminthes and 276 without helminthes were bacteriologically examined, including 23 samples infested and 145 non-infested specimens of the main vector, Citellophilus tesquorum. Statistical differences in the proportion of samples contaminated by unpretentious bacteria and effect of flea abundance in the sample on the number of colonies grown have not been revealed. In 2018, 26 cultures of bacteria of the genera Serratia, Staphylococcus, Pseudomonas, Acinetobacter, Macrococcus, and Bacillus were isolated from 23 samples of entomoparasitic nematodes. Possible ways of their penetration into flea imagoes are discussed.

In the present study, a stimulating effect of a new synthetic organoselenium compound 2,6-dipyridinium-9-selenabicyclo[3.3.1]nonandibromide (974zh) on the immunogenic activity of the vaccine strain Yersinia pestis EV NIIEG was revealed. After infection with the virulent plague strain, the survival rate of laboratory mice immunized with the vaccine strain grown on Hottinger’s agar in the presence of 974zh (300 μg/ml) increased in comparison with control animals immunized with the Y. pestis EV NIIEG culture grown on agar without the studied compound. Plasmid screening of cultures grown on medium with and without 974zh showed that plasmid DNA of Y. pestis EV culture grown in the presence of 974zh had broader bands in the control grown without 974zh. This phenomenon can indicate activation of replication of plasmid DNA of Y. pestis EV under the influence of the experimental compound.

Background. Pseudotuberculosis remains a serious healthcare problem, which determines the expediency of developing the express methods for its early diagnosis. To detect the pathogen, we designed test system for dot-immunoassay (DIA) based on antibodies labeled with silver nanoparticles (SNPs) isolated from hyperimmune rabbit serum obtained against killed cells of Yersinia pseudotuberculosis of O:1b serovariant.The aim. To assess the possibility of using dot-immunoassay for express identification of Y. pseudotuberculosis cultures isolated from clinical material and environmental objects at the initial stage of bacteriological study during laboratory diagnosis of the disease.Methods. We used the materials from the outbreak of pseudotuberculosis in the Krylovskaya Boarding School of the Bakcharsky district of the Tomsk region in 2021. Specific antibodies from hyperimmune rabbit sera obtained against Y. pseudotuberculosis 3704 particulate antigen of O:1b serotype were labeled with SNPs and used in DIA on nitrocellulose membranes with visualization of reaction results with a solution of a physical developer. The presence of the causative agent of pseudotuberculosis in the test material was inferred by the formation of gray spots of different intensity (from 4+ to 1+).Results. All Y. pseudotuberculosis strains isolated using bacteriological method on the second day of the study from clinical material obtained from sick people and environmental objects were detected in DIA at concentrations ≥ 3.1 × 104 microbial cells per milliliter (m.c./ml).Conclusion. The designed test system for dot-immunoassay using SNPs as a marker of specific antibodies for the detection of Y. pseudotuberculosis in cultures isolated from swabs from vegetables and clinical material from patients, including those with mixed infection, allows us to detect a specific corpuscular antigen with a high sensitivity (≥ 3.1 × 104 m.c./ml), providing express identification of isolated cultures at the initial stage of bacteriological study.

Ixodid tick communities in Primorskii Territory are characterized by significant species diversity. The species richness of Ixodidae is higher on the Primorye islands than on the mainland. Bi- and polydominant pasture ixodid communities occur only on islands. Of the eight islands surveyed in 1982–1983, only Putyatin Island had a monodominant tick community with predominance of Haemaphysalis concinna Koch, 1844. This paper is focused on the current structure of adult ixodid hemipopulations on Putyatin Island. Ticks were collected from vegetation by flagging on May 17–21, 2021 at different sites of the island. The following species were recorded (in descending order of abundance): Dermacentor silvarum Olenev, 1932, Haemaphysalis concinna Koch, 1844, Ixodes persulcatus Schulze, 1930, H. japonica douglasi Nuttall et Warburton, 1915, and I. pavlovskyi pavlovskyi Pomerantzev, 1946. In total, 354 ixodid ticks were collected, and their low abundance was observed. According to the data of 2021, H. longicornis Neumann, 1901 was no longer found on Putyatin Island, I. pavlovskyi was recorded for the first time, the abundance of D. silvarum increased significantly, and that of I. persulcatus increased to a lesser extent. The possible causes of changes in the structure of ixodid tick communities are discussed. Putyatin Island currently has a bidominant complex of ixodid ticks, with 45.8

The aim of the work was to analyze the epizootic and epidemiological situation on leptospirosis in the territory of the Russian Federation in 2013–2022 and to forecast its development in 2023. The long-term dynamics of leptospirosis incidence in the Russian Federation tends to decrease. Cases were registered in 58 constituent entities of the Russian Federation, in all federal districts. The highest incidence rates were noted in the North-Western Federal District. When studying the material from small mammals using bacteriological, immunological and molecular-biological methods, Leptospira circulation was detected in 52 entities of the Russian Federation, in all federal districts. In 2023, sporadic cases of infection are to be expected in the territories of the North-Western Federal District, the Central Federal District, and the Southern Federal District; imported cases of infection from countries with subequatorial and equatorial climates are not excluded.

The aim of the study was to analyze the genetic structure of populations and the patterns of evolutionary variability of the novel coronavirus infection in the Siberian and Far Eastern Federal Districts. Materials and methods. 1033 SARS-CoV-2 genomes from samples from individuals diagnosed with COVID-19 from eight entities of the Siberia and Far East between December 2020 and November 2021 were assessed. Sequencing was performed on the MinION Oxford Nanopore platform using the ARTIC v.3 protocol. The degree of SARS-CoV-2 genetic isolation was estimated applying the Fst criterion. Phylogenetic analysis was carried out using maximum likelihood method and Bayesian phylogenetic inference. A nonparametric Bayesian Skyline Plot (BSP) model was used to reconstruct population dynamics. Results and discussion. The original SARS-CoV-2 variant (B.1) was identified in 100 % of the cases at the initial stages. The Alpha variant was detected in March-June, 2021; Beta – in single samples in March-May, 2021. Delta was first identified in April, 2021. The maximum degree of SARS-CoV-2 genetic isolation (Fst=0.18) was established for the most remote territories (Altai Territory ↔ Republic of Buryatia and Altai Territory ↔ Irkutsk Region). A relatively free circulation of the virus was detected between Irkutsk Region, Republic of Buryatia and Krasnoyarsk Territory. According to the results of population genetic tests, a sharp increase in the effective virus population size was the determining mechanism of SARS-CoV-2 genetic diversity formation. Reconstruction of population dynamics in BEAST (BSP model) has revealed the consistency of trends in the genetic diversity of the virus and the number of active cases. Two subclusters have been identified in the Delta cluster, consisting predominantly of samples isolated in the Irkutsk Region and Krasnoyarsk Territory. Change in the dominant variant of SARS-CoV-2 has been traced in dynamics. Molecular-epidemiological data point to the multiple pathways of spatial expansion of different SARS-CoV-2 genotypes into the constituent entities with generation of individual monophyletic clusters and further intra- and extraterritorial spread of the decedents.

Relevance . COVID-19 is accompanied by high production of cytokines - immune molecules, imbalanced regulation of which leads to disruption of the immune response. Therefore, the study of cytokine status in both vaccinated and re-vaccinated patients is necessary to develop an immunoprophylaxis strategy for COVID-19. Aim. To evaluate the cytokine status in COVID-19 survivors and vaccinated employees of a health care facility against this disease. Materials and Methods. Production levels of cytokines (IL-4, IL-10, IFN-γ and TNF-α) were determined by quantitative enzyme immunoassay in serum of 144 volunteers. Results and discussion . A significant 1.5-fold increase in IL-10 and 2.0-fold increase in TNF-α was found in the group of re-invaccinated overinfected volunteers, and a 2.0-fold decrease in IL-4 compared with the vaccinated group. An inverse correlation between IL-4 and IFN-γ levels and timing after the disease was detected. A significant decrease in IL-4 in survivors (Omicron variant) and an increase in IL-10 in the survivors at the beginning of the pandemic as compared to other re-vaccinees was established. In the vaccinated group, regardless of the vaccine used, IL-10 and TNF-α decreased significantly after revaccination. No statistically significant differences were found between the cytokine status parameters in the survivors before and after vaccination. The predominance of the cellular component of immunity was established in all the examined groups, and the highest proportion of persons with a humoral immune response was detected among the vaccinated volunteers, while the highest proportion of persons with a mixed immune response was detected among the overexperienced non-vaccinated patients. Conclusions . The results obtained supplement the available data on coronavirus infection and indicate the need for further research.

The aim of the work was to assess the epidemic situation on plague in the world and epizootic activity of natural plague foci of the Russian Federation in 2022. Following the implementation of comprehensive preventive interventions plans, there was a decrease in the epizootic activity of the Gorno-Altai high-mountain and Tuva mountain natural foci, the cessation of plague epizootics in the Central Caucasian high-mountain focus. The total area of epizootics in the Russian Federation in 2022 reached 248.3 km2, which is 7 times less than in 2021. Infected animals were not found in the Tersko-Sunzhensky low-mountain, Dagestan plain-piedmont, Caspian North-Western steppe, Volga-Ural steppe, Trans-Baikal steppe, Volga-Ural sandy, Caspian sandy, East Caucasian high-mountain natural foci. Persistence of tense epizootiological situation in 2023 is predicted for the territory of the Altai Republic and the Republic of Tuva. The prospects of using the GIS portal of the Russian Anti-Plague Institute “Microbe” of the Rospotrebnadzor for an operational assessment of the actual epidemiological situation in natural plague foci are substantiated.

Advanced molecular-genetic methods for the diagnosis and typing of Yersinia pestis ssp. pestis in the field and clinical material are used for epidemiological surveillance of plague in the Saylyugem natural focus. The aim of the work was to study the spatial genotypic structure of Y. pestis ssp . pestis in the transboundary Saylyugem natural plague focus using MLVA25 typing. Materials and methods. The MLVA25 typing of 160 strains of Y. pestis ssp. Pestis isolated in the Saylyugem natural plague focus in 2012–2021 was carried out. Phylogenetic tree construction was performed with the help of UPGMA and MST methods. Results and discussion. The Y. pestis ssp. pestis strains isolated from the Saylyugem natural plague focus were differentiated into 15 MLVA types by the 25 VNTR loci cluster analysis. The studied strains form a homogeneous complex of MLVA25 types without marked geographical distribution across seven spatial groups. The analysis of the frequency of occurrence of the tandem repeats number for three variable loci of Y. pestis ssp. pestis strains shows the significant differences between the samples from the Mongolian and Russian parts of the Saylyugem natural plague focus. The most pronounced differences in spatial genotypic structure are traced through the yp4280ms62 locus.