Whole-genome sequencing clarifies brucellosis outbreak transmission in Shandong, China
Photo by National Cancer Institute / Unsplash
Key Takeaway
Consider integrated molecular surveillance to support brucellosis control in endemic regions, noting observational limitations.
This observational cohort study investigated a 2023 brucellosis outbreak in Shandong Province, China, involving 26 related cases. The study integrated field epidemiological investigation with whole-genome sequencing, including multilocus variable-number tandem repeat analysis and core-genome single-nucleotide polymorphism genotyping.
Ten Brucella strains were isolated: 9 were Brucella melitensis biovar 3 and 1 was biovar 1. Nine biovar 3 strains formed a single clonal cluster with 0 SNP difference. Molecular-epidemiological concordance was 38.5% (10 out of 26 cases). The outbreak originated from a flock of infected lambs introduced by an index case in 2022, spreading through local livestock trading networks. Phylogenetic analysis indicated co-circulation of multiple lineages in the region.
No safety or tolerability data were reported, as this was a molecular epidemiological investigation. A key limitation is that 61.5% of cases could not be definitively linked due to missing epidemiological data or lack of isolate recovery. The findings are observational and describe transmission patterns, not causal interventions.
Practice relevance is that integrated molecular surveillance systems are valuable in key endemic regions to support human brucellosis control. However, certainty is limited by missing data for many cases, and findings should not be extrapolated to other regions without evidence.
View Original Abstract ↓
BackgroundThis study integrated epidemiological investigation with whole-genome sequencing to elucidate the transmission chain and pathogen characteristics of a 2023 brucellosis outbreak in Shandong Province, providing evidence for targeted prevention and control.MethodsTransmission chains were reconstructed through field epidemiological investigations, active case finding, and retrospective data review. Isolated strains were cultured and identified, followed by molecular tracing using multilocus variable-number tandem repeat analysis (MLVA) and core-genome single-nucleotide polymorphism (cgSNP) genotyping. Epidemiological and molecular data were integrated to assess transmission links.ResultsA total of 26 related cases were identified in this outbreak. Epidemiological investigation revealed that the outbreak originated from a flock of infected lambs introduced by an index case in 2022, with subsequent spread through local livestock trading networks affecting multiple villages. Ten Brucella strains were isolated, including nine of Brucella melitensis biovar 3 (B. melitensis bv. 3) and one of B. melitensis bv. 1. cgSNP analysis showed that the nine bv. 3 strains formed a single clonal cluster (0 SNP difference) and grouped with historical Shandong strains, indicating sustained local transmission. The bv. 1 strain represented a separate infection event, genetically distinct from the main outbreak cluster. Integrated analysis confirmed a complete molecular-epidemiological concordance for 38.5% (10/26) of cases; the remaining 61.5% could not be definitively linked due to missing epidemiological data or lack of isolate recovery. Phylogenetic analysis further indicated co-circulation of multiple lineages in the region.ConclusionThis outbreak was primarily driven by the trade of locally infected sheep, facilitating regional spread. High-resolution molecular typing effectively complemented traditional epidemiology by uncovering concealed transmission chains and revealing the co-circulation of multiple lineages. These findings underscore the value of integrated molecular surveillance systems in key endemic regions to support human brucellosis control.
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