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Molecular epidemiology of Brucella abortus in Shandong, China: high-resolution insights from combined MLVA-16 and core genome SNP analysis

Year: 2025

Type: article

Abstract: Introduction: in human clinical samples from Shandong, China, highlights an ongoing zoonotic threat. Methods: strains isolated from human patients since 2021 using a combination of conventional biotyping, Multiple Locus Variable-number Tandem Repeat Analysis (MLVA), and core-genome SNP (cgSNP) analysis. Results: Epidemiological data indicated that infections primarily occurred in middle-aged men with occupational livestock exposure. Molecular typing revealed biovar 3 as the predominant type (91.7%), dominated by MLVA-8 genotype 36 and its corresponding MLVA-11 genotype 72 (66.7%). MLVA-16 distinguished 12 unique genotypes. The phylogeny based on cgSNP classified the strains into clades C1 (11 bv. 3 strains) and C2 (one bv. 1 strain). Within clade C1, nine strains in subclade C1-III exhibited ≤119 SNP differences, eight of which formed a local clonal transmission chain (≤52 SNPs) and shared MLVA-11 genotype 72. Subclade C1-I contained two strains with novel genotypes resulting from variations at the Bruce18 and Bruce43 loci. The sole C2 strain differed by only 3 SNPs from the A19 vaccine strain, suggesting a potential vaccine-related origin. Genetic links were also identified with strains from other Chinese provinces, among them Heilongjiang and Inner Mongolia, as well as from several countries, including Mongolia and Russia. Discussion: These findings revealed a complex epidemiological pattern in Shandong, primarily characterized by local transmission chains with occasional external introductions, provided a scientific basis for targeted brucellosis control strategies.

Source: Frontiers in Microbiology

DOI: 10.3389/fmicb.2025.1695815