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.

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