The review summarizes the data of modern domestic and foreign studies on the mechanisms of evolutionary adaptation of the plague pathogen to transmissive spread by arthropods. The data on the molecular basis of the rapid formation of a highly pathogenic bacterium due to the acquisition of new genetic information; structural and functional changes in the genome, causing the disruption of functionality of some genes that prevent survival in the vector are presented. The stage of the complex life cycle of the pathogen associated with the peculiarities of its stay in the vector’s organism and its tactics of evasion from the action of antibacterial substances formed by the flea is considered. The importance of biofilm formation for effective transmission of the pathogen is discussed. A complex cascade of transcriptional regulators of biofilm in Yersinia pestis is considered, which includes activators and repressors of biofilm formation, as well as regulators of synthesis or modification/transport of exopolysaccharide. The hms-dependent mechanism of biofilm formation in Y. pestis is described in detail, as well as the impact on biofilm formation through the regulation of LPS-related genes and its role in the modification and transport of biofilm exopolysaccharide. The data from our own studies on the variability of genes involved in biofilm formation in the main subspecies of the plague pathogen in comparison with non-main subspecies of the plague pathogen, as well as on the ability of strains of different subspecies to form biofilm not only in the proventriculus of the flea, but also on the cuticle of soil nematodes of the Tylenchida and Rhabditida orders and the genus Panagrolaimus are presented. The latter allows us to assume the possible participation of soil and entomoparasitic nematodes in the removal of Y. pestis biofilms from the soil to the above-ground biocoenosis of the natural plague focus.

In 2023, 305 cases of human infection with tularemia agent were registered in the Russian Federation. Epizootic manifestations of the infection, varying in the degree of intensity, were identified in 65 constituent entities of the country, and sporadic cases of human tularemia were reported in 15 regions of Russia. The unfavorable epidemic situation persists in the Republic of Karelia (189 patients with tularemia), Stavropol Territory (35 people), and a surge in the incidence is also recorded in the Donetsk People’s Republic (53 patients), which accounts for 91 % of all tularemia cases in the country. A total of 82 Francisella tularensis cultures were isolated in 9 entities of the Russian Federation. 923,729 people were vaccinated and revaccinated against tularemia in 2023. Based on the data analysis, obtained in 2023, epidemic complications in the form of sporadic cases of the disease among the unvaccinated population in the following territories are most likely to occur in 2024: the Central Federal District – in the Vladimir, Oryol, Ryazan and Tver Regions, and Moscow city; Northwestern Federal District – in the Republic of Karelia, Arkhangelsk, Vologda Regions and in St. Petersburg; Southern Federal District – in the Republic of Crimea, Volgograd and Rostov Regions; North Caucasus Federal District – in the Stavropol Territory; Volga Federal District – in the Republic of Mordovia, as well as in the Kirov and Saratov Regions; Ural Federal District – in the Yamal-Nenets Autonomous District, KhantyMansi Autonomous District and Tyumen Region; Siberian Federal District – in the territories of certain districts of the Krasnoyarsk Territory, Omsk, Kemerovo, Tomsk, Novosibirsk and Irkutsk Regions; Far Eastern Federal District – in the Republic of Sakha (Yakutia).

The review features the situation on Crimean-Congo hemorrhagic fever (CCHF) in the world and the analysis of the epidemiological and epizootiological situation in the Russian Federation in 2023. The number of CCHF cases (26) in Russia was 2.3 times less than in 2022, and 71.6 % lower than the long-term average (in 2013–2022 – an average of 88.8 cases per year, mortality (8 %) is 2.4 times higher than the long-term average (3.3 %). The epidemically significant indicator of the abundance of the main vector of the CCHF virus, ticks Hyalomma marginatum, was 5 times higher than the threshold value (abundance index for cattle – 15.5) at long-term observation points in April. For the first time, one case of CCHF disease was registered in a new epidemically active territory – in the Botlikh and Novolaksky districts of the Republic of Dagestan. For the first time in the Zaporozhye Region, RNA of the CCHF virus was detected in ticks H. marginatum and Rhipicephalus rossicus. Markers of CCHF virus were found in 0.67–18.27 % of samples, CCHF virus variants of the genetic line Europe 1 were circulating on the territory of Russia in 2023. According to the forecast of the epidemic situation for 2024, CCHF morbidity is likely to increase in the south of the European part of Russia. The recommendations for undertaking preventive measures have been provided.

The review is devoted to discussing the results of survey in the Hissar high-mountain natural plague focus on the territory of the Republic of Tajikistan in 2015–2023. Regular examination of the focus was carried out in 1970–1991. According to its results, the main carrier of the plague pathogen was the juniper vole, in the population of which a strain of the non-main subspecies central asiatica (0.PE4) of Hissar biovar (0.PE4h) was steadily circulating, the strain considered avirulent for humans. During that period, 853 strains were isolated in the focus, of which 799 (93.7%) were from the juniper vole and its fleas. Secondary carriers – the silver vole, the pygmy wood mouse, and the gray hamster – were rarely involved in epizootics. The red marmot, which has epidemiological significance due to its hunting by the local population, occupies a special position in the focus. Socio-political phenomena at the end of the 20th – early 21st century caused a long break in the work of the Tajik Plague Control Station. In 2008, the Station was transformed into the Republican Center for Combating Quarantine Diseases under the Ministry of Health and Social Protection of the Population of the Republic of Tajikistan. In 2015, studies were resumed, but carried out on a small scale. In 2021–2023, epizootiological monitoring in the Hissar focus was performed jointly with Russian specialists with the testing of field material samples for plague and other natural-focal infections. Currently, against the background of low numbers and population density of small mammals and their blood-sucking ectoparasites – potential carriers and vectors of zoonoses – the circulation of agents of plague, tularemia, pseudotuberculosis, tick-borne viral encephalitis, Ixodidae tick-borne borreliosis, human granulocytic anaplasmosis, human monocytic ehrlichiosis has not been registered. Markers (DNA) of causative agents of leptospirosis and intestinal yersiniosis have been identified. Joint Tajik-Russian cooperation on issues of ensuring the epidemiological well-being of the population of the Republic of Tajikistan must be continued.

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.

Over the past 200 years since the moment of E. Jenner’s discovery, vaccination continues to be the leading strategy for protection against infectious diseases, but commercially available live attenuated and inactivated vaccines have a number of serious drawbacks. Bacterial strains should be completely attenuated in live vaccines, while maintaining a high degree of immunogenicity. However, the majority of attenuation methods currently used makes potential vaccine strains more susceptible to the action of various host defenses, reducing the ability to persist in the body of the vaccinated individual in quantities and for periods sufficient for formation of long-term and intense immunity. Inactivation of microorganisms underlying the production of killed vaccines, applying various reagents and /or physical factors, can disrupt the native conformation of antigenic epitopes located on bacterial cell surface, which leads to a decrease in immunogenicity. This review examines a promising biotechnological platform for the development of vaccines based on the methodology of regulated delayed gene expression and repression of genes, which was developed to resolve the above-mentioned contradictions.

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.

The paper presents an analysis and assessment of risks of complication of epidemiological situation regarding cholera in the Russian Federation and a forecast for 2024. It briefly characterizes the dynamics of the epidemic process around the world during the last decade (2013–2022). The forecast of cholera importation into the Russian Federation, due to activity of the epidemic process in endemic countries, has been confirmed. In 2023, two cases of cholera importation from India were reported. It was established that the toxigenic strains isolated from patients belonged to the currently dominant in the world “post-Haitian” group, including in India and Bangladesh, with the genotype ctxB7 tcpA^CIRS rtxA4a VSP-IIΔ0495-0512. Furthermore, non-toxigenic Vibrio cholerae O1 strains were isolated from samples of biological material from persons arriving from India, containing preCTX prophage and distinct from the strain (ctxAB^– tcpA^EТ–) isolated from a patient with acute intestinal infection (Zaporozhye Region, Melitopol). Nontoxigenic NAG vibrios were isolated from 13 patients with acute intestinal infections, which is 1.9 times more than in 2022. Regardless of importations, a strain of V. cholerae O1 (ctxB1⁺tcpA^EТ) of the “pre-Haitian” group was isolated from a water sample of a surface reservoir. 52 non-toxigenic V. сholerae O1 strains were found on the territory of 11 constituent entities of the Russian Federation, which is 18.9 % more than in 2022. In 2024, epidemiological risks of cholera importation from endemic countries to any administrative territory of the Russian Federation remain. The risks of epidemic manifestations of cholera are especially high in the territories of the constituent entities of the Russian Federation which are under ongoing emergency, due to migration processes, and the impact of other risk-forming factors that contribute to an increase in the degree of contact of the population with water bodies contaminated with cholera vibrios. If epidemic foci of cholera are to emerge in a neighboring country, there will be a high probability of spread of this infection in the stated constituent entities of the Russian Federation and in other territories of southern Russia. In the absence of epidemic manifestations of cholera, the possibility of occasional detection of toxigenic O1 serogroup strains in water samples due to unidentified introductions from cholera-affected areas cannot be ruled out.

An analysis of the epidemiological situation on West Nile fever (WNF) in the Russian Federation in 2023 has revealed an increase in the number of cases (210) relative to the year 2022 by 6.3 times, the long-term average value by 1.2 times. Manifestations of the epidemic process were characterized by a significant expansion in the number of territories, where cases of the disease were confirmed (24 constituent entities, including in 13 – for the first time); a long epidemic season; an increase in the proportion of cases with a severe clinical course and fatality rate, which significantly exceeded the long-term average across Russia (8.5 and 1.2 %, respectively). Patients with fever and other similar manifestations of WNF were examined for the presence of the disease markers in 50 entities of the Russian Federation. Continued trend towards a decrease in the volume of diagnostic studies carried out by medical organizations and an increase in the time required for the etiological deciphering of disease cases has been established. Serological examination of sample groups of healthy population was performed in 65 entities. Epizootiological monitoring was carried out in 74 entities, rate of infection of carriers and vectors with West Nile virus (WNV) was confirmed in 14 entities. In the territory of the European part of Russia and the North Caucasus, the circulation of WNV lineages 1, 2 and 4 with the dominance of WNV lineage 2 has been established. Data on the genetic heterogeneity of WNV lineage 2 strains that circulated in Russia in 2023 have been obtained. Based on an analysis of climatic factors, a forecast of WNF incidence in the Russian Federation for 2024 was prepared.

This paper provides an analysis of the results of joint work of Russian and Congolese infectious disease specialists and epidemiologists to decipher the etiology and causes of the outbreak of intestinal infections in Dolisie (Republic of the Congo) in the summer of 2023. It has been found that the increase in the incidence of intestinal infections was caused mainly by the agents of typhoid fever and dysentery; tropical malaria was a combined pathology. No cases of cholera patient detection were registered. Failure of water supply system, domestic disrepair, and low public awareness about prevention of intestinal infections contributed to the active transmission of pathogens. The combination of epidemic process manifestations testified to the aquatic nature of the outbreak. Also, cases of pathogen transmission through contact household route were recorded, food transmission was not excluded. Patients with severe and complicated forms of typhoid fever and shigellosis accounted for 50 % of those hospitalized. There was delay in seeking medical care. The available regimens of antibacterial therapy were ineffective, since there was no possibility of laboratory confirmation of the diagnosis with determination of sensitivity to drugs. Uncontrolled treatment facilitated the emergence of antibiotic resistance in pathogens, prolonged bacterial release and subsequent spread of infection. Infectious disease specialists and epidemiologists of the Rospotrebnadzor provided consulting and practical assistance to Congolese colleagues, developed and presented recommendations for optimizing anti-epidemic and therapeutic measures, taking into account the results of assessment of the causes for onset and development of the outbreak.

The paper describes the epidemiological situation in the countries of the world in terms of the incidence of Hantavirus diseases. The results of an epidemiological analysis of the incidence of hemorrhagic fever with renal syndrome (HFRS) in the Russian Federation in 2023 by federal districts are presented and a forecast for 2024 is made. In 2023, 5 093 cases of HFRS were registered in the Russian Federation (3.47 per 100 thousand population). The incidence was reported in 7 out of 8 federal districts of the country. The age structure was dominated by people in the 30–59 age category (65.7 %); 247 cases of the disease were noted among children under 17 years of age. The proportion of the male population was 70.3 %. 63.2 % of the total number of cases was registered among the urban residents. The mortality rate was at the level of 0.49 % – 25 lethal outcomes. Analysis of the data has revealed a decrease in the incidence of HFRS in Russia by 27.2 % as compared to the previous year. However, the data from epizootiological monitoring and the results of laboratory research of field material indicate a continuing tense situation in the country as a whole. In a number of regions, a high risk of complications of the epidemiological situation is predicted (mainly, in the constituent entities of the Volga and Central Federal Districts). Moderate risks of developing local complications of the epidemiological situation at the level of long-term average morbidity are expected to be realized in the entities of the Northwestern, Ural and Far Eastern Federal Districts. Sporadic cases of the disease in the territory of the Southern Federal District are not excluded. The aggravation of the situation on HFRS in the territory of the North-Caucasian and Siberian Federal Districts is not anticipated in 2024.

The review provides the summarized and updated information on the current distribution of the tick Hyalomma marginatum in the natural Crimean hemorrhagic fever (CHF) focus in Russia. The work is based on the analysis of numerous literature sources, as well as the evidence from the personal collecting of ticks during long-term field research. In addition, the collection of ticks of the Stavropol Research Anti-Plague Institute of the Rospotrebnadzor and the database of H. marginatum collections in various regions of southern Russia were used. When delineating the boundaries of the H. marginatum areal and the CHF focus, we also deployed maps of the epidemiological survey of the focus, weekly and annual final reports on the CHF incidence from the Rospotrebnadzor Administrations. H. marginatum inhabits all regions of the Southern Federal District and the North-Caucasian Federal District, as well as the Crimean Peninsula and the south of the Saratov Region. The northern border of the areal reaches the Lugansk People’s Republic, Rostov, Volgograd, and Saratov Regions. H. marginatum is widely disseminated in the territory of Kalmykia and the Astrakhan Region. In the North Caucasus, it inhabits the entire flatland up to the foothills of the Greater Caucasus. The tick is widely distributed in the Stavropol Territory, populating the entire region. In the mountainous part of the Krasnodar Territory, this species is absent, but common in the rest of the areas. Beyond that, it is found on the Black Sea coast. In Karachay-Cherkessia, Kabardino-Balkaria, North Ossetia and Ingushetia, the tick lives in the northern steppe regions of the republics, in some places it invades the foothills. In Chechnya and Dagestan, the species widely inhabits the steppes and semi-deserts of the Terek-Kuma Interfluve. Moreover, in Dagestan, H. marginatum lives across the plain and foothill territory of the republic and even reaches the highlands up to a height of more than 2000 m above sea level. In addition, it is widely disseminated on the Crimean peninsula, both the flatland and the mountainous part.

The aim of this work was to rank the territory of the Caspian sandy natural plague focus (43) by the risk of epizooty emergence using the MaxEnt model.

Materials and methods. The archival data on epizootic manifestations of plague over the past 35 years, aggregated by the Stavropol Anti-Plague Institute of the Rospotrebnadzor, the Dagestan, Elista, Astrakhan PCSs of the Rospotrebnadzor, were used for model design. 615 archive plague detection points were converted into the coordinate system (1980–2015). 87 publicly available bioclimatic variables BioClim were deployed to construct the MaxEnt model. Applied weather and climatic factors of the BioClim database are averaged over a multiyear period.

Results and discussion. The MaxEnt model has a very high degree of reliability (AUC=0.975), with a sufficiently high predictive ability (AUC=0.973). According to the generated model, the Caspian sandy natural plague focus has a heterogeneous structure in terms of the probability of epizooty registration and can be divided into five zones. The most significant factors for the model are the following indicators: the average temperature of the wettest quarter, solar radiation in November, the average temperature of the driest quarter, the amount of precipitation in the coldest quarter, wind speed in May, the amount of precipitation in the wettest quarter, and the average air temperature in September. The data obtained allow for targeted search for plague epizootics and can be used to adjust boundaries of a surveyed natural focus in the future.

The aim of the study was to assess the current epidemiological situation on Ixodidae tick-borne borreliosis (ITBB) (2017–2022) on the Black Sea coast of the Krasnodar Territory, to study the species composition of Borrelia.

Materials and methods. Ixodidae ticks, Ixodes ricinus, Haemaphysalis concinna, H. inermis, Rhipicephalus sanguineus, were examined for infection with tick-borne borreliosis pathogens, followed by DNA sequencing of isolates. Species identification of Borrelia was carried out based on analysis of the nucleotide sequence of the 16S rRNA gene fragment using BLAST algorithm. Additionally, the OspC genotype was determined for isolates of pathogenic genovariants through comparing the obtained sequences with reference ones in the MEGA 5 program. The data were processed applying the cartographic method using the QGIS 2.18 software.

Results and discussion. Between 2017 and 2022, 101 cases were registered on the Black Sea coast of the Krasnodar Territory, which accounted for 1.6 % of all ITBB cases in the Krasnodar Territory. The number of complaints with tick bites in Sochi was up to 191.4 per 100 thousand population. During the study, the predominant Borrelia geno-species on the territory of the Black Sea coast of the Krasnodar Territory was determined using sequencing – Borrelia lusitaniae (78.1 %). The circulation of geno-species B. garinii (6.8 %), B. valasiana (5.7 %), B. afzelii (3.6 %), B. miyamotoi (2.6 %), B. tanukii, B. bissettii (1.6 % each) was also observed. For Borrelia pathogenic species, appurtenance to OspC geno-groups was ascertained: four isolates were assigned to invasive OspC geno-groups, of which three B. afzelii isolates were genogroup A8, one B. garinii isolate was G7. High rate of infection of ticks with Borrelia was recorded in the surveyed area (up to 94.5 %). Borrelia of pathogenic species account for only 10.4 % of the total number of isolates studied. Mostly, genovariants that rarely cause diseases in humans (B. lusitaniae, B. valasiana, B. bissettii) and non-pathogenic Borrelia (B. tanukii) were found, which indicates a low risk of infection with ITBB pathogens.

The aim of the work was to determine the cytotoxicity and the influence of polycyclic derivatives of the framework series on the replicative properties of the SARS-CoV-2 virus in Vero-E6 cell culture in vitro.

Materials and methods. The virus inhibiting effect of 50 adamantane and bicyclo[3.3.1]nonane derivatives with carbocyclic and heterocyclic substituents was investigated. The studies were carried out on Vero-E6 cell culture by assessing the cytopathic effect of the virus. The impact of the compounds on the replicative properties of the SARS-CoV-2 virus was estimated by the decrease in virus titer in the presence of the compounds compared to the control. Based on the virus titer values in the presence of a series of successively decreasing concentrations of the compound, the 50 % effective concentration was calculated.

Results and discussion. A study of polycyclic derivatives of the framework series has identified two compounds with antiviral properties against the SARS-CoV-2 virus. Among bicyclo[3.3.1]nonane derivatives containing heterocyclic fragments, compound No. 15144 has showed an inhibitory effect against the SARS-CoV-2 virus. The protective effect of the compound was manifested in maximum tolerable concentration (MTC) (70.0 μg/ml) and ½ MTC (35.0 µg/ml). A decrease in virus titers under the influence of MTC by 0.95 lg TCD₅₀/ml, in ½ MTC (35.0 μg/ml) – by 0.35 lg TCID₅₀/ml has been detected. The effective concentration (EC50) value of the compound No. 15144 was 64.0 μg/ml, the MTC/EC50 ratio was 1.09. Compound No. 14838 (adamantane derivative containing carbocyclic fragments) had less pronounced antiviral activity. As a result of research, it has been established that sample No. 14838 at a dose of MTC (45.0 μg/ml) reduces the infectious titer by 0.78 lg TCD₅₀/ml, in ½ MTC (22.5 μg/ml) by 0.15 lg TCD₅₀/ml compared to the control. The EC50 value of compound No. 14838 was 37.0 μg/ml, the MTC/EC50 ratio was 1.22.

The aim of the work was to conduct a comparative phylogenetic analysis based on wgSNP of complete genomes of Brucella melitensis strains circulating in the territory of the Russian Federation.

Materials and methods. wgSNP typing of 412 B. melitensis strains of the main genetic lineages of brucella from different regions of the world, including 64 strains isolated in the regions of the European and Asian parts of the Russian Federation, was performed. DNA sequencing was conducted on the “Ion GeneStudio S5 Plus” platform (“Life Technologies”, USA) using the “Ion Plus Fragment Library Kit library preparation” (“Life Technologies”, USA), according to the “Ion 520™ & Ion 530™ Kit – Chef” protocol (Revision D.0).

Results and discussion. It has been established that the strains circulating in Russia belong mainly to genotype II, which has a wide geographical distribution across the territory of Eurasia. At the same time, subgenotype IIh prevails in the regions of Siberia, and Iii – in the European territory of the country. For the first time, sets of specific SNPs have been identified that allow for intraspecific differentiation of B. melitensis strains. The obtained results made it possible to determine the probable routes of introduction of the causative agent of brucellosis into the territory of the Russian Federation from China and the countries of the Middle East. The prospect of using an optimized wgSNP typing scheme to solve urgent problems in the field of molecular epidemiology of brucellosis is demonstrated. It includes determining the genotype and subgenotype of the pathogen associated with the probable geographical region of origin of infection, and identifying the genetic relations between strains with high accuracy.

Rickettsiae, which are obligate intracellular bacterial parasites, have a life cycle commonly associated with arthropod vectors and animal hosts. Rodents are recognized as their natural reservoir hosts and play a role in transmitting the bacteria to humans through arthropod vectors. The true extent of rickettsial infections in Vietnam remains underestimated due to a limited understanding of the disease’s epidemiology, resulting in a significant public health burden.

The aim of this investigation was to assess the prevalence of Rickettsia in wild-living rodents in Dien Bien, Son La, and Phu Tho provinces of Northern Vietnam between 2020 and 2022.

Materials and methods. A total of 396 wild-living rodents were collected from the Northern provinces of Vietnam during 2020–2022. Real-time polymerase chain reaction (PCR) was employed to detect the percentage of Rickettsia-positive specimens. Subsequently, the ompB and 17kDa genes were extracted, amplified, and sequenced from the Rickettsia-positive rodents.

Results and discussion. Among the 396 rodents examined, the majority were Rattus norvegicus (56.1%), followed by R. tanezumi (37.4%), R. nitidus (2.5%), and R. germaini (1.8%). R. korodentsensis and R. argentiverter constituted the remaining rodents, accounting for 2.2% of the total. The real-time PCR analysis revealed that 27 blood samples out of the 396 rodent samples collected, tested positive for Rickettsia (6.81%). R. germaini was shown to have the highest positive rate 1/8 (12.5%), followed by R. nitidus 1/10 (10.0%), R. tanezumi 14/149 (9.5%), and R. norvegicus 11/222 (4.9%). No other tick-borne pathogens were detected in any of the provinces. Sequencing of the positive samples as regards the ompB and 17kDa genes revealed the closest relation to R. felis. These findings highlight the potentially high risk of R. felis infection in humans and animals within the studied areas.

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.

The aim of the study was to assemble full-length nucleotide sequences of the chromosome and plasmids for 13 Yersinia pestis strains from 11 natural plague foci located in the Russian Federation, using data from two sequencing technologies.

Materials and methods. Y. pestis strains were grown on Hottinger’s agar (pH 7.2) at 37 °C. DNA was isolated using phenol-chloroform extraction. For the MinIon genetic analyzer (Oxford Nanopore), DNA fragments were prepared by ligation according to a modified protocol. For the Ion S5 genetic analyzer (IonTorrent), sample preparation was carried out according to the standard protocol for obtaining a library with a DNA fragment size of 400 nucleotide pairs (bp). The resulting single reads were filtered by average quality Q30 for IonTorrent and Q7 for Oxford Nanopore.

Results and discussion. DNA fragments containing 50 000 or more nucleotide pairs were prepared for subsequent sequencing using nanopore sequencing technology (Oxford Nanopore). The Trycycler algorithm was applied for hybrid assembly of the genome of Y. pestis strains and correction of errors arising during this process, allowing the obtainment of full-length nucleotide sequences of the chromosome and plasmids for each genome of the strain. The nucleotide sequences of the chromosomes of 13 Y. pestis strains from 11 natural foci of plague located in the Russian Federation have been deposited in the international genetic database NCBI GenBank. It has been established that to assemble full-length genomes of Y. pestis strains, a significant number of reads with a size of 50 000 bp or more is required, and the use of the Trycycler algorithm allows one to generate a more accurate assembly of complete bacterial genomes.

At present, bacteriophages are considered as an alternative to antibiotics in prevention and treatment of bacterial infections, in particular cholera.

The aim of the work was to demonstrate a method to obtain synthetic bacteriophage against Vibrio cholerae. Vibriophage N4 was selected as a subject for the study.

Materials and methods. The genome sequence of vibriophage N4 (38.5 kb) was taken from the NCBI GenBank database. The sequence was divided into gene blocks of 1500–2000 bp. The gene blocks, in turn, were split into oligonucleotides. Sequence partitioning was carried out using the BAC-browser software that we have developed. Oligonucleotides were chemically synthesized; gene blocks were assembled from them. After that, the complete genome of vibriophage N4 was synthesized from the obtained gene blocks. The assembly of the synthetic genome took place in two stages. At the first stage, gene block cassettes of 5–7 pieces with sizes ranging from 7 to 10.5 thousand bp were generated via homologous recombination in yeast. The resulting cassettes were then amplified and used for in vitro assembly using 5’-3’ exonuclease and thermostable DNA polymerase. The resulting preparation was used for electroporation of V. cholerae cells.

Results and discussion. The synthetic genome of vibriophage N4 was delivered into the V. cholerae strain M818 O1 biovar El Tor using electroporation. As a result, the formation of lytic plaques on the lawn of V. cholerae was observed. The range of technologies we have developed: software for assembly design, enzymes and buffers for the synthesis of gene blocks and their crosslinking by homologous recombination in vitro, the method for producing large-sized assemblies in yeast can be used to obtain artificial bacteriophages with a rational genome design.

Currently, the Russian Anti-Plague Institute “Microbe” produces diagnostic immunoglobulins used in laboratory diagnostics of plague pathogen. One of the important stages in obtaining this category of drugs is the process of adsorption and removal of cross-reacting antibodies to increase the specificity of the drug. For this purpose, inactivated cells of Yersinia pseudotuberculosis strains are used.

The aim of the work was to assess the possibility of using immunochemical methods to analyze the adsorption properties of bacterial cells, followed by an assessment of the impact of cultivation method and conditions, and the variant of the strain used on the adsorption properties of bacterial cells.

Materials and methods. Cultivation was carried out on solid and liquid nutrient media; cells were inactivated by temperature and chemical exposure. Adsorption activity was assessed using immunoblotting and inhibitory enzyme-linked immunosorbent assay. Statistical processing of the results was performed using two-factor analysis of variance.

Results and discussion. The suitability of immunoblotting and inhibitory ELISA methods for qualitative and quantitative assessment of the adsorption properties of bacterial cells has been demonstrated. It has been established that the adsorption properties of bacterial cells are influenced by the method of inactivation and the application of substrate feeding; the method of cultivation does not affect the adsorption properties of cells.