Problems of Particularly Dangerous Infections
Russian Research Anti-Plague Institute “Microbe”
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Epidemiological Situation on Tick-Borne Viral Encephalitis in the Russian Federation in the Context of a Changing Climate (2016–2025) and Incidence Forecast for 2026
The aim of this review was to characterize the epidemiological situation regarding tick-borne viral encephalitis (TBVE) in the Russian Federation between 2016 and 2025 and to provide a forecast of TBVE incidence for 2026 for federal districts and constituent entities of the highest epidemiological risk. During 2016–2025, the average annual number of individuals affected by tick bites in the RF was 498575.1. In 2020–2021, an upward trend in this indicator was noted in certain entities of the Volga and Northwestern Federal Districts, among others. Climate warming has shifted the onset of Ixodidae tick activity to the last week of March. A lengthening of the epidemic season is observed. In 2025, 1,807 TBVE cases were identified, corresponding to an incidence rate of 1.24 per 100,000 population (compared to the long-term average of 1.17 per 100,000). The five entities with the highest incidence are Kirov Region, Krasnoyarsk Territory, Tuva Republic, Khakassia Republic, and Perm Territory. A total of 44 fatal outcomes were recorded (case fatality rate – 2.4 %). Based on the data from 2016–2025, 17 entities at highest epidemiological risk have been identified, eight of which are located within the Siberian Federal District. The average tick infection rate in the Russian Federation for 2025 (tested via PCR and ELISA) does not differ from the long-term average. A comparison of the genetic structure of tick-borne encephalitis virus strain samples from 1937–1989 and 1990–2025 has showed an increase in the proportion of the Siberian subtype from 54.8 to 89.7 %, while the ratio of individual genetic lineages within the Siberian subtype remained invariable. The volumes of specific and non-specific TBVE prevention measures in 2025 increased compared to 2024 and corresponded to the target figures in all federal districts. According to the forecast, the TBVE incidence in the Russian Federation in 2026 is projected to be 1.14 per 100,000 population, with a confidence interval from 0.95 to 1.32 per 100,000. An increase in morbidity is possible in the Volga and Far Eastern Federal Districts, while the epidemiological situation in the remaining districts is not likely to change.
Ixodidae Tick-Borne Borrelioses in the World. Epidemiological Situation in the Russian Federation in 2025 in Comparison with Long-Term Data and Forecast for 2026
An overview of the epidemiological situation on Ixodidae tick-borne borreliosis (ITBB) in the world and the Russian Federation in 2025 in comparison with long-term values is presented. A forecast for 2026 is made. In 2025, the maximum number of ITBB cases was registered in the Russian Federation (9,698) over the past 15 years. Relative to the long-term average, the incidence rates of ITBB increased in 4 federal districts: Central (CFD), Volga, Southern (SFD) and North-Caucasian (NCFD) ones; the proportion of CFD in the overall structure of ITBB incidence expanded significantly (55.43 %). The number of constituent entities with a reported incidence of ITBB has risen to 84, and an increase in incidence has been noted in half of them. During the period of 2013–2025, the peculiarities of trends in the epidemic process of ITBB in territories of varying degrees of epidemiological risk persisted. In the majority of entities with a long-term average annual incidence (LTAA) above 8.4 0 /0000, a downward trend or relative stability in the incidence of ITBB has been revealed, with the exception of Moscow and the Kaluga Region, where a pronounced upward trend was noted. In 10 out of 19 regions with LTAA between 4.2 and 8.3 0 /0000, an upward trend was observed, while in 8 – a decrease in morbidity. The trend towards an increase in the incidence of ITBB was detected in 14 out of 24 entities with LTAA from 1.6 to 4.1 0 /0000 and in 19 of the 29 regions with low LTAA (up to 1.5 0 /0000). The analysis of trends in the development of the epidemic process and calculations of the probable incidence rate allows us to conclude that for most federal districts, the incidence rate of ITBB in 2026 will vary around the confidence intervals of the long-term average values, with the exception of the CFD, SFD and NCFD, where an increase in the number of cases of ITBB is probable. Effective control of the epidemic situation on ITBB is possible provided that it is maintained and enhanced. For regions such as Moscow, Saint Petersburg; Moscow, Voronezh, Lipetsk, Nizhny Novgorod, Kostroma, Ryazan, Tula, Kaluga, Bryansk, Kirov, Kursk, Orel, Tver, Tyumen, Penza and Irkutsk Regions, Altai and Trans-Baikal Territories, the Republics of Buryatia and Mordovia, constituent entities of the Southern Federal District and the North-Caucasian Federal District, increase in the volume and improvement of the quality of preventive measures, including hygienic education of the population, strengthening zoological and entomological monitoring of the activity and structure of natural foci, are required.
Epidemiological Situation on Anthrax in the World in 2025, the Forecast for 2026 in the Russian Federation
The results of assessment of the epidemiological situation on anthrax in the world in 2025 are provided; the dynamics of anthrax incidence in the period of 2016–2025 and the forecast for 2026 in the Russian Federation are presented. In 2025, one outbreak of anthrax was registered in Russia in the Nizhny Novgorod Region, with seven heads of small ruminants infected; there was no infection of humans. Over the last decade (2016–2025), compared to the previous one (2006–2015), the number of registered outbreaks of anthrax infection decreased by 2.7 times, the number of sick people – by 1.1 times, and the number of sick farm animals increased by 11.9 times – due to the epizootics in the Yamal-Nenets Autonomous District of the Ural Federal District. The unfavorable situation on anthrax was noted in four neighboring countries: Kazakhstan, Kyrgyzstan, Tajikistan and Georgia. The most intense epizootiological and epidemiological situation has been recorded in Asian and African countries with large-scale epizootics among wild animals in African national parks. Human infection was caused by contact with sick animals during forced slaughter, processing and ingestion of contaminated meat. The incidence of anthrax in animals and humans in the Russian Federation in 2026 will be determined by the completeness of the complex of preventive measures and, if fully implemented, will be limited to sporadic cases. There remains a potential risk of complications in the epidemiological situation due to the possibility of importing sick animals and livestock products from countries affected by anthrax to Russia, primarily from Central Asia to the border regions of the Russian Federation.
Epidemiological Situation on Hemorrhagic Fever with Renal Syndrome in 2025 in the World and in the Russian Federation, Incidence Forecast for 2026
The aim of this review is to describe the global epidemiological situation on hemorrhagic fever with renal syndrome (HFRS), provide a comparative analysis of the epidemiological situation on HFRS for 2000–2025 in the constituent entities and federal districts of the Russian Federation, and outline an incidence forecast for 2026. HFRS remains a widespread disease in the Western Pacific Region, Southeast Asia, and Europe. In the Russian Federation, the majority of HFRS cases are registered in the Volga Federal District, which accounts for over 80 % of all cases. In 2025, 4,912 cases of HFRS were diagnosed in the Russian Federation, a 31 % increase as compared to the previous year (3,396). The incidence rate (3.36 per 100,000 population) was below the long-term average for the period of 2013–2024, excluding 2020 and 2021 (5.06). There were 12 deaths (lethality rate – 0.24 %, mortality – 0.01 per 100,000 population). The epidemiological process was most active in the territory of 11 entities of the Volga Federal District: the Republic of Bashkortostan, the Udmurt Republic, Kirov, Samara, Penza, Nizhny Novgorod, Orenburg, Ulyanovsk Regions, the Mari El Republic, the Republic of Mordovia, and the Republic of Tatarstan. The review presents the results of epizootiological monitoring. For the purpose of forecasting and differentiating the areas by the level of incidence, epidemiological zoning of the entities of the Russian Federation was carried out based on the value of the potential epidemic risk indicator. Six groups of territories have been identified: those with an extremely high predicted risk, those with high, with above-average, average, low, and with minimal risk. Six regions are classified as having an extremely high prognostic risk of HFRS infection, including the Republic of Bashkortostan, the Republic of Mordovia, the Republic of Tatarstan, the Udmurt Republic, the Chuvash Republic, and the Yaroslavl Region.
Organization of Laboratory Diagnostics of Anthrax in Mobile Laboratories in the Republic of Tajikistan in 2024–2025
The aim of the work was to organize laboratory diagnostics of anthrax using a mobile laboratory, including for the verification of the clinical diagnosis of anthrax in the Republic of Tajikistan. Materials and methods. 17 clinical samples and one sample of beef were analyzed using molecular-genetic (PCR, sequencing) and bacteriological methods. The susceptibility of isolated Bacillus anthracis cultures to antibacterial agents was determined applying the disk diffusion method. Results and discussion. The complex epidemiological and epizootiological situation on anthrax in the Republic of Tajikistan necessitates the improvement of epidemiological surveillance of this disease. The diagnosis of anthrax in the Republic is still based on the clinical presentation, without mandatory laboratory confirmation. In 2024–2025, with the advisory and practical support of Russian specialists, diagnostic tests for the presence of the anthrax pathogen were conducted in mobile laboratories set up at the premises of medical facilities. In 2024, when 5 samples of clinical material from patients who were treated with antibacterial drugs were examined, no B. anthracis DNA was detected, and no culture of the anthrax microbe was isolated. In 2025, when studying 12 samples taken before treatment from 7 patients and 1 sample of cattle meat collected from the focus of infection, DNA of B. anthracis was detected in all cases. Cultures of the anthrax pathogen were isolated and identified; their sensitivity to antibacterial drugs and appurtenance to the phylogenetic group A.Br.047 were determined. The obtained results allowed for confirming the clinical diagnosis of anthrax, to prescribe adequate etiotropic therapy, and to promptly carry out anti-epidemic measures. The effectiveness of using mobile laboratories for prompt diagnosis of anthrax has been demonstrated, specifically under conditions of limited infrastructure, remote areas, and a shortage of specialized stationary laboratories.
Clarification of the Systematic Position of a Representative of the Genus Escherichia Isolated from Soil
The aim of the work was to investigate the phenotypic and genetic properties of Escherichia marmotae and its phylogenetic relationships with previously described strains of this species. Materials and methods. Microorganism cultures were grown on LB agar at 37 °C. Biochemical (API 20 E), catalase, oxidase, and hemolytic activities were determined. Antibiotic susceptibility was assessed using the disk diffusion method. Species identification was established applying the MALDI-TOF MS method. Whole genome sequencing was performed on the MGI platform with subsequent SNP analysis. Results and discussion. The strain under study has the following characteristics: gram-negative short, weakly motile rods; small, bright crimson colonies with a metallic sheen are formed on Endo medium, on blood agar – γ-hemolysis; oxidase-negative, catalase-positive. The genome contains a number of important markers that determine pathogenicity: siderophores, the virulence factor virK, type I fimbriae, yad fimbriae, curli amyloid proteins, and type III secretion system genes. Phenotypic resistance to cefixime, imipenem, gentamicin, tobramycin, and amikacin has been identified. Genetically, the strain is most closely related to the isolate obtained in China in 2012 and is not closely related to strains isolated in the Russian Federation in 2021. Phylogenomic analysis of E. marmotae strains revealed a dispersed structure of isolates of various origins, with no clear patterns regarding geographic origin or affiliation with specific animal species. Thus, strains of the E. marmotae species are virtually indistinguishable from Escherichia coli based on phenotypic characteristics. Reliable identification of E. marmotae strains is possible using MALDI-TOF MS, 16S rRNA sequencing, or whole genome sequencing.
Etiological Deciphering of Imported Cases of Community-Acquired Pneumonia in the Irkutsk Region in 2024
In 2024, two cases of community-acquired pneumonia (CAP) imported from Thailand were registered and etiologically deciphered in the Irkutsk Region, including the first case of acute melioidosis resulting in death, which was diagnosed for the first time in the Russian Federation. In the second case, Acinetobacter radioresistens was isolated from a patient with CAP. The aim of the work was to conduct indication and species identification of pathogens causing community-acquired pneumonia, obtained from biological material from patients who had arrived from Thailand to the Irkutsk Region. Materials and methods. The culture of a microorganism isolated from a liver sample of a patient with the fatal outcome, preliminarily identified by mass spectrometry as a causative agent of the genus Burkholderia and clinical material (blood, throat swab, sputum, urine) from a patient with suspected melioidosis were studied. The research was performed using bacteriological, bacterioscopic, molecular-genetic, proteomic, and serological methods of laboratory diagnostics. Results and discussion. In the first imported case, a culture of Burkholderia pseudomallei was isolated from a patient with a postmortem clinical diagnosis of community-acquired bipartite pneumonia; rapid identification of the causative agent of melioidosis was carried out using MALDI-TOF MS and PCR methods. For the purpose of in-depth identification, the isolated culture was studied by a range of laboratory diagnostic methods for melioidosis. The sensitivity of the isolated B. pseudomallei strain to some first- and second-line antibacterial drugs was established, and its species resistance to penicillins, aminoglycosides, and macrolides was confirmed. In the second imported case of community-acquired pneumonia, the causative agent of melioidosis and its DNA were not found in the patient’s clinical material. A culture was isolated from the patient’s urine sample, which was identified by mass spectrometry as Acinetobacter radioresistens. In view of the growing number of imported cases of exotic infections in the Russian Federation, including melioidosis, it is necessary to increase the alertness of medical personnel, incorporate melioidosis in the differential diagnostics of community-acquired pneumonia in people with a “traveler’s history”, maintain the readiness of specialized laboratories, strengthen awareness-raising among the population traveling to regions endemic for dangerous infectious diseases, and ensure effective interdepartmental cooperation within the framework of sanitary protection of the territory of Russia in order to establish an etiological diagnosis of community-acquired pneumonia and correct treatment scheme.
Evaluation of the Results and Planning of an Epizootiological Survey Using a Rated Epizooty Index by the Example of the Southern Part of the Caspian Sandy Natural Focus of Plague
The discovery of a plague epizooty in a natural focus is almost a random event. Differentiation of territories within natural plague foci based on the probability of epizooty registration significantly increases the chances of its identifying. The aim of the work was to calculate the rated epizooty index (EI) using the example of the Caspian sandy natural plague focus (southern part), differentiate the surveyed sectors according to the probability of registering epizootics, and provide proposals for improving the epizootiological survey. Materials and methods. Data on 335 sectors, primarily spanning 1981–2024, were analyzed. Conventional and rated epizooty indices (CEI and REI) were calculated, the rated one allowing for correcting the detection bias effects. Results and discussion. Detection bias during focal territory surveys has been confirmed. Compared to conventional EI, the REI has revealed a 1.5-fold increase in low-risk epizooty sectors (low REI values). A mathematically rigorous criterion is proposed to identify low-prospect sectors for epizooty detection (probability threshold: 0.95). This allows reallocating efforts to under-surveyed sectors or those with high REI values. This approach enhances epizootiological monitoring efficiency, optimizes resource allocation, and refines plague focus boundaries.
Development of a Technology for Spatial Risk Analysis of Tick-Borne Infections Based on Emergency Notification Data
The aim of the study was to develop and test a technology for the spatial analysis of the epidemiological risk of tick-borne infections based on geo-encoded emergency notification data. Materials and methods. A retrospective spatial analysis of a continuous sample of emergency notifications for the Irkutsk Region over the period of 2023–2024 was conducted, including cases of tick bites (n=21,585) and tick-borne viral encephalitis (n=171). The geo-encoding of residential addresses and presumed exposure sites was performed automatically using an R-based program through the DaData application programming interface, followed by mapping using geographic information systems. Results and discussion. The proportion of emergency notifications containing textual information suitable for geo-encoding was 48.1 % for tick bites and 52.0 % for tick-borne viral encephalitis cases. Concordance between the municipality of exposure and the patient’s district of residence was observed in only 29.6 % of tick bite cases and 30.3 % of tick-borne viral encephalitis cases. In most instances, the municipal district of the presumed tick attack site differed from the patient’s place of residence. The proposed spatial analysis approach has revealed hidden zones of tick-borne viral encephalitis infection risk in territories not included in the official list of endemic districts, and demonstrated a discrepancy between areas with high calculated incidence levels and locations with the highest concentration of infection events. The developed technology improves the accuracy of assessing the territorial risk of tick-borne infections. Implementing geoencoding features for emergency notification data into the tick-borne infection epidemiological surveillance system will ensure objective zoning for planning targeted preventive measures.
Genomic Characteristics and Phylogeny of the Burkholderia pseudomallei I-16 Strain, the Causative Agent of the First Imported Case of Melioidosis in Russia
The aim of this study was to identify genetic features and determine the phylogenetic relationships of Burkholderia pseudomallei I-16 strain, isolated from post-mortem sample in Irkutsk Region in 2024 from a case of flash lethal melioidosis imported from Thailand. Materials and methods. Molecular-genetic analysis of the B. pseudomallei I-16 genome was performed in comparison with 34 genomes from public databases using PubMLST, IslandViewer 4, NGphylogeny, and iTOL v6. Results and discussion. B. pseudomallei I-16 was assigned to the rather rare and geographically restricted sequence type ST23. Phylogenetic analysis based on the core genome concatenated sequences showed clustering of B. pseudomallei I-16 in a single clade with strains from Thailand, Laos, and Cambodia; the closest strains, DR10212A and 708a of Thailand origin, differed from I-16 by 820 and 958 core genome loci, respectively. One probable integrated plasmid and three prophages were detected in the B. pseudomallei I-16 genome. Analysis of variably present B. pseudomallei virulence factors on the predicted MGEs of B. pseudomallei I-16 revealed the effector-immunity pairs: the T6SS-linked effector TOX-REase-5 and its neutralizing protein, the DNA deaminase toxin DddA and the neutralizing protein CdiI. In addition, clusters of the T6SS and T4SS genes, the T3SS effectors HrpK and ChbP, the genes encoding the virulence factor TspB and the Zot toxin, the YadA family adhesins BoaA and BpaC, the delta-toxin of the Cry8Ea1 family and its secretory protein VirK, the genes encoding the hemolysin secretion/activation protein ShlB/FhaC/HecB, and the filamentous hemagglutinin fhaB3 were detected. This indicates that the I-16 strain possesses a sufficiently representative additional set of virulence factor genes acquired through horizontal transfer, which is the most likely cause of the high virulence of the B. pseudomallei I-16 strain.
Identification of New Genome Structure Features in Non-Toxigenic Strains of Vibrio cholerae O1 Biovar El Tor ctxAB-tcpA+
The aim of the study was to comparatively analyze the structure and prevalence of pathogenicity, drug resistance, and persistence genes among non-toxigenic Vibrio cholerae O1 strains, biovar El Tor ctxAB−tcpA+. Materials and methods. Nucleotide sequences of whole genomes were assessed for 73 toxigenic and 33 non-toxigenic strains of cholera vibrios applying multilocus sequence typing of the strains using the MLST 2.0 online service on CGE (Center Genomic Epidemiology) platform and phylogenetic analysis using MrBayes v.3.2.7a. Results and discussion. New genomic features of non-toxigenic V. cholerae El Tor strains with the ctxAB−tcpA+ genotype, belonging to the L3 phylogenetic lineage, have been identified. Significant genetic differences were revealed between ctxAB−tcpA+ strains from L3 line. It has been established that, based on ST type, the presence of ICE and VSP-II mobile elements, the allelic profile of pathogenicity genes (tcpA, rtxA) and drug resistance genes (gyrA and parC), the presence of the VC2346 gene, a number of non-toxigenic strains are substantially genetically similar to toxigenic strains and are, presumably, derivatives of typical or genetically modified V. cholerae strains. Phylogenetic analysis has confirmed the pronounced genetic similatity of those isolates to toxigenic strains and demonstrated their affiliation to the phylogenetic lineage of epidemically dangerous strains, namely, L2. Thus, among the non-toxigenic cholera vibrios biovar El Tor ctxAB−tcpA+, strains with genetic markers of the cholera pathogen have been found, which indicates that they originated from toxigenic ones and that there is a need to develop diagnostic tools for differentiating non-toxigenic strains with different pathogenic potential.
Forecasting the Consequences of the Introduction of Mpox Virus into Russia
The cessation of vaccination after the eradication of smallpox led to a decrease in the level of herd immunity of the world’s population. Currently, the risk of national and international spread of Mpox is assessed as “high”. The introduction of MPXV clade 1b can be carried out by land or air transport by citizens of foreign countries or Russian tourists returning from a vacation abroad. The aim of the study was to predict the consequences of the introduction of MPXV clade 1b into the territory of Russia. Materials and methods. The data from published foreign and domestic scientific papers on the spread of Mpox, the values of average herd immunity and average basic reproductive number, as well as data characterizing the duration of post-vaccination immunity against orthopoxvirus infections were used. Results and discussion. A forecast of the outbreak development as a result of the introduction of MPXV clade 1b into the territory of Russia in the absence of anti-epidemic measures has been made for three scenarios: a single imported case taking into account the size of the immune stratum of the population, a household outbreak, an outbreak in a closed community. The results of the forecast allow us to conclude that the introduction of MPXV clade 1b into the territory of Russia may lead to the emergence of a local or municipal emergency. In any of the considered scenarios, after the isolation of patients and those who have been in contact with them, the outbreak will cease.
Molecular-Genetic Characteristics of Yersinia pestis Strains from the Volga-Ural Sandy Plague Focus
The aim of the work was to establish the phylogenetic diversity of subpopulations of Yersinia pestis strains from the Volga-Ural sandy natural plague focus during the period of epizootic and epidemic activity between 1912 and 2002 and to determine their geographic distribution. Material and methods. One hundred and three samples from Volga-Ural sandy focus (1912–2002) were studied. High-throughput sequencing was performed on the MGI platform (DNBSEQ-G50RS, China) using MGIEasy Fast FS Library Prep Set and MGIEasy UDB Primers Adapter Kit A. To process the data and carry out the assembly of obtained raw short reads, Unicycler v0.4.9, FastQC v0.11.9 software was used. The analysis of VNTR loci was conducted using the TandemReapeatFinder program; the agglomerative clustering method was applied for hierarchical clustering (AgglomerativeClustering, scikit-learn v1.7.0 library). The SNP-typing was performed via Snippy v4.6.0. To construct phylogenetic tree we used the method of Maximum Likelihood in PhyML 3.1 (500 bootstrap replicas). Results and discussion. Whole-genome SNP-analysis and phylogenetic reconstruction of the population structure have identified the main subpopulations common in the Volga-Ural sandy focus; the SNP genotypes of Y. pestis strains have been established, and their marker SNPs determined. It has been suggested that the cause of plague outbreak in 1945 could be genotype Pricasp 2. VNTR-analysis has revealed 57 MLVA25-genotypes and the most variable VNTR-loci (ms46 и ms62). Results of conducted SNP- and VNTR-analysis indicate active changes in the zones of intra-focal circulation as well as the consistent evolution of the medieval biovar of Y. pestis strains, the phylogenetic branch 2.MED1 in Volga-Ural sandy focus.
Comprehensive Study of the Circulation of Spotted Fever Group Rickettsioses Pathogens in Certain Districts of the Saratov Region in 2025
Tick-borne rickettsioses are one of the leading causes of vector-borne infections in the Russian Federation. In Saratov Region, during 2021–2024, genetic markers of spotted fever group (SFG) rickettsiosis pathogens, identified as Rickettsia raoultii, R. conorii and R. slovaca, were detected in 8 species of Ixodidae ticks and 3 species of gamaside mites. A serological survey of the population in Engels region in 2024 revealed IgG antibodies to R. conorii in 6.4 % of samples; however, no SFG rickettsiosis foci or human cases have been officially registered in the region. The aim of this study was to detect genetic markers in ticks and examine the population for the presence of specific antibodies to the causative agents of SFG rickettsioses in certain districts of the Saratov Region in 2025. Materials and methods. A total of 1,411 specimens of hard and soft ticks and mites collected in 9 districts and the Saratov municipality were tested using PCR. Additionally, the ELISA method was applied to examine 400 blood sera from the residents. Results and discussion. The presence of Rickettsia spp. SFG DNA was confirmed in tick suspension samples of 6 tick species. Ticks were collected in 8 districts and in the Saratov municipality. Genetic markers of R. conorii were identified in 2 tick species. Laboratory testing of serum samples for the presence of antibodies to R. conorii revealed the following: 46 samples containing IgG immunoglobulins and 2 samples containing IgM antibodies. The results obtained indicate the circulation of pathogenic rickettsiae in the Saratov Region and the possible existence of natural foci of SFG rickettsioses, which necessitates the inclusion of this group of infections in the epidemiological surveillance system.
Study of Type 6 Secretion System in Non-Toxigenic Strains of Vibrio cholerae O1 Biovar El Tor and Their Competitive Features
The aim of the work was to study the structure of the genes of type 6 secretion system in non-toxigenic strains of Vibrio cholerae O1 serogroup, biovar El Tor and to identify their competitive features. Materials and methods. The studies were conducted on non-toxigenic strains isolated in the Russian Federation from patients or environment between 1981and 2017, stored in the State Collection of Pathogenic Bacteria of the Russian Anti-Plague Institute “Microbe” of the Rospotrebnadzor. For bioinformatics analysis, the BLAST v.2.15.0 and BioEdit v.7.0.9.0 algorithms were applied. The nucleotide sequences of complete genomes presented in NCBI GenBank were utilized. The competitive test was set in autoclaved river water according to the method of R. Freter et al. (1981). Results and discussion. It has been established that the composition of type 6 secretion system clusters of in ctxA–tcpA+ isolates is identical to that of toxigenic V. cholerae O1 El Tor strains and includes a large cluster and three additional – Aux-1, 2, and 3. Moreover, Aux-3 corresponds to the Aux-3P type, characteristic of toxigenic isolates, in terms of size and gene composition. The structure of 88.9 % of the studied loci is also prototypical. The exception is three strains with a single nucleotide substitution in the gene encoding the VgrG-3 effector. A large cluster and Aux-2 have been detected in ctxAB–tcpA– strains. The Aux-1 cluster is absent in the genome of 22 % of the strains, and in the remaining ones only the marginal gene encoding hemolysin is present. Only two ctxAB–tcpA– strains contain Aux-3, which corresponds to the Aux-3E type, characteristic of aquatic vibrios. Variability in the structure of the majority of the studied genes of these strains has been revealed. When ctxAB–tcpA– and ctxAB–tcpA+ strains were co-cultivated, almost all ctxAB–tcpA+ isolates exhibited a competitive advantage. The exception was the ctxAB–tcpA– strain of V. cholerae M1337, which produced increased amounts of exopolysaccharide, enhancing its competitive properties. The coexistence of ctxAB– tcpA+ isolates and Aeromonas hidrophila 401, which has a functional type 6 secretion system, has been demonstrated.
Infection of Ixodidae Ticks with Pathogens of Tick-Borne Infections in Trans-Baikal Territory
Trans-Baikal Territory is endemic for tick-borne encephalitis virus, borreliosis, and rickettsiosis. Cases of human granulocytic anaplasmosis and human monocytic ehrlichiosis are also reported. The aim of this study was to analyze the prevalence of tick-borne diseases and assess epidemiological risks in the Aginsky, Dul’durginsky, Kyra, Kalgansky, Nerchinsko-Zavodskoj districts of Trans-Baikal Territory. Materials and methods. During a period of three years (2022–2024), 2095 ticks of three species (Ixodes persulcatus, Haemaphysalis concinna, and H. japonica) were collected from five districts of the Territory and 60 small mammals from two districts. Results and discussion. In a PCR study of 2071 tick suspensions for four pathogen groups, markers for one or more pathogens were detected in half of them. Two or more pathogens were found simultaneously in 19.8 % of arthropod suspensions. Markers for Anaplasma, Ehrlichia, and TBEV were found two times more often in combinations than as mono-variants. The opposite pattern was observed when detecting DNA of Borrelia, which was more common in single variants. Borrelia markers were identified in average in 51.1 % of the ticks studied, Anaplasma markers – in 16.9 %, Ehrlichia markers – 9.7 %, and TBEV – 3.2 %. RNA isolates of the Baikal subtype from the Alkhanay National Park are genetically close to previously studied TBEV strains, confirming the continued circulation of the virus in this area over a long term. In a study of small mammals, markers of one or more pathogens were detected in six of them, using PCR for four pathogen groups. The Baikal subtype of the TBEV was detected in one Myodes rufocanus. The epidemiological situation on tick-borne infections in the Trans-Baikal Territory remains tense.
Molecular-Genetic Characteristics of Brucella abortus Strains from the Dzhida Region of the Republic of Buryatia under Conditions of Epizootic Activation of Brucellosis in 2023–2024
The aim of the study was to identify genetic features and possible origin of Brucella abortus strains that caused the epizootic outbreak of brucellosis in the Republic of Buryatia in 2023–2024. Materials and methods. The studied B. abortus strains, isolated from pathoanatomical material from cattle in the Republic of Buryatia in 2023–2024 in the area adjacent to Mongolia, were examined bacteriologically, followed by pathogen DNA sequencing and bioinformatic genome analysis. Bayesian phylogenetic analysis was performed in BEAST v2.7.5. Results and discussion. The genomes of the strains have been characterized; a comparative analysis of strain variability has been conducted in relation to the vaccine strain B. abortus 82 and strains isolated in Mongolia in 1999 and 2014. It was established that all studied strains belong to a single clonal branch of B. abortus with sequence type 2. The 2023–2024 outbreak B. abortus group emerged approximately 58 years ago (95% HPD: 31.2–86.7) and is closely related to strains isolated in Mongolia in 1999 and 2014. The evolution rate of this group was 1.8·10–7 substitutions per site per year (95% HPD: 2.5·10–8 – 1.84·10–6 substitutions per site per year). The unique mutation distinguishing this group of strains from B. abortus 82 and Mongolian strains is a defect in the rbsB gene caused by a mutation resulting in a stop codon within the reading frame. This gene is involved in energy-dependent transport of extracellular D-ribose into the cell and may potentially reduce the bacterium’s ability to reproduce inside host cells. As a result of the molecular-genetic study, the causes and patterns of occurrence of the brucellosis outbreak among cattle in the Republic of Buryatia in 2023–2024 has been established.
Evaluation of the Effectiveness of Methods for Detecting Francisella tularensis in the Study of Field Material and Characterization of Isolated Strains of the Pathogen
The aim of the work was to perform a comparative analysis of the informative value of diagnostic methods in the study of various environmental objects for the presence of tularemia agent markers; molecular-genetic characterization of strains of the causative agent of tularemia. Materials and methods. A comparative analysis of effectiveness of diagnostic methods for tularemia indication: PCR (polymerase chain reaction), AbNT (antibody neutralization test), ICT (immune-chromatographic test) in various samples of field material from the foci of the Rostov Region, Lugansk People’s Republic, Donetsk People’s Republic, Zaporozhe and Kherson Regions for the period of 2020–2023 was carried out. The molecular-genetic characteristics of the strains isolated from various sources was obtained using VNTR typing followed by the construction of a dendrogram applying the NJ method. Results and discussion. The comparative analysis of the effectiveness has shown that the biological method remains the gold standard for detecting live bacteria, Francisella tularensis, in field material. Serological methods based on the detection of specific antigens are a reliable marker of the pathogen circulation in the focus of tularemia in cases where it is not possible to isolate live culture. If the AbNT results were questionable, the samples were additionally investigated using immune-chromatographic tests. It has been established that AbNT is the most informative method when studying the material from the nesting and burrowing substrate, bird regurgitates and droppings of predatory mammals. At the same time, according to our data, PCR diagnostic methods are the most adequate ones in relation to such environmental objects as hay, grain, fodder, water, etc. The 31 F. tularensis cultures studied are represented by six individual VNTR genotypes. The largest number of genotypes (4 out of 6) was found among small mammals, two genotypes were indicated in ticks and one – in a water sample. The combined use of serological and molecular-biological methods makes it possible to increase the reliability and accuracy of detecting the causative agent of tularemia in environmental objects.
The Preparation of Chromatographically Purified Anti-Smallpox Immunoglobulin from Equine Blood Serum
The aim of the work was to obtain chromatographically purified anti-smallpox immunoglobulin from equine blood serum and evaluate its properties. Materials and methods. The horse blood serum containing antibodies to the vaccine virus, L-IVP strain, was used. Сhromatographic purification of serum was carried out on Akta Avant preparative chromatograph (GE HealthCare, Sweden), molecular parameter control at the stages of immunoglobulin production was conducted on the LC-20ad HPLC system (Shimadzu, Japan). The biological properties of immunoglobulin were evaluated in rabbits, white mice, and guinea pigs. The level of specific virus neutralizing antibodies was determined in the neutralization reaction on the chorionallantoic membrane (CAМ) of 12-day chicken embryos. Results and discussion. The technology for obtaining chromatographically purified anti-smallpox immunoglobulin from equine blood serum has been developed. At the initial stage, the immune blood serum of horses was purified by filtration through glass fiber cassette-type filters from fibrin sediment, residual quantity of lipids and lipoproteins, and then the immunoglobulin fraction was precipitated with a saturated solution of ammonium sulfate. At the next stage, ammonium salts, low molecular weight fractions, residual quantity of albumins and euglobulins were removed using ion exchange chromatographic purification. At the final stage, dimers, polymers, and aggregates of immunoglobulins were eliminated using gel filtration. The experimental series of immunoglobulin prepared using the developed technology is characterized by a high degree of purification. The monomer content in the finished product is at least 99 %, and the specific activity by titer of specific neutralizing antibodies – at least 1:16000.
Seroprevalence of Echinococcosis and Assessment of Behavioral Risk Factors for Echinococcoses in the Jeti-Oguz District of the Kyrgyz Republic using ELISA
Echinococcosis remains a relevant parasitic disease and a serious medical and social issue. Epidemiological features, risk factors, and preventive measures for cystic and alveolar echinococcosis are of particular interest, as these diseases have a chronic course and may lead to disability and death. The aim of the study was to assess the seroprevalence of echinococcosis and to analyze behavioral risk factors for echinococcosis among the population of the JetiOguz district, Issyk-Kul Region, Kyrgyz Republic. Materials and methods. The study involved questionnaire data and serological testing results from 826 individuals residing in 10 settlements of the Jeti-Oguz district, Issyk-Kul region, Kyrgyz Republic. ELISA was used to detect signs of current or past infection and to assess disease prevalence in the studied population. The study had a cross-sectional design and included a sociological survey, serological methods, and statistical analysis. Data processing was performed using Microsoft Excel and SPSS software packages. Results and discussion. The overall seroprevalence of echinococcosis was 8.2 %, with the highest rates observed in the 60–69 age group (14.3 %) and among women (66.2 %). Analysis of behavioral factors (presence and keeping of domestic animals, deworming, contact with dogs, and feeding of dogs with innards of slaughtered animals) did not reveal statistically significant associations with seropositivity (OR 0.395–1.215; 95% CI included 1; p>0.05), indicating the complex nature of infection transmission. The findings highlight the need for targeted preventive and educational programs, screening examinations, and control of sanitary safety in the endemic region.
System of Yersinia pseudotuberculosis MLVA14-Typing Based on Multiple-Locus Variable-Number Tandem Repeat Analysis
Yersinia pseudotuberculosis bacterium is the etiologic agent of pseudotuberculosis, a natural-focal disease reported in various regions of the world. Strains of pseudotuberculosis microbe are characterized by significant genetic diversity and differ in pathogenicity and ability to cause group and sporadic diseases in humans. Since 2022, 1,090 cases of pseudotuberculosis infection have been identified in the Russian Federation; however, the incidence remains underestimated. Current advances in molecular-genetic technologies facilitate the development of highly effective methods for detecting and differentiating Y. pseudotuberculosis strains. The aim of this study was to develop an effective MLVA14 typing system for intraspecific genetic differentiation of Y. pseudotuberculosis, based on multilocus VNTR analysis. Materials and methods. This study involved molecular-genetic and phylogenetic assessment, as well as in silico O-genotyping of 94 Y. pseudotuberculosis strains based on their nucleotide sequences deposited in the NCBI RefSeq database. Results and discussion. The serological affiliation, pathogenicity factors, and genetic group assignments have been determined. Phylogenetic relationships of the Y. pseudotuberculosis strains used in this study have been characterized, fourteen not previously described VNTR loci with distinct properties and discriminatory abilities identified. Flanking primers have been designed for the identified molecular targets using the Primer-BLAST web service. Applying in silico, MLVA typing of strains was performed and a cladogram of relationships was constructed, demonstrating that the developed MLVA14 method discriminates closely related Y. pseudotuberculosis strains into the same groups as whole-genome SNP analysis, but using a smaller number of molecular targets. The developed MLVA14 typing method is highly effective for intraspecific genetic differentiation of Y. pseudotuberculosis strains.