Phylogenetic Evidence for Nationwide Expansion Brucella melitensis Lineages Drives the Re-Emerging and Epidemic of Human Brucellosis in Jiangsu, China

Wang Weixiang¹Zhou Lu²Teng Ge¹Zikang Yan¹Lan Huang³Zhongming Tan²Zhiguo Liu^4*Songning Ding¹Zhenjun Li⁴

• ¹Nanjing Center for Disease Control and Prevention, Nanjing, Jiangsu Province, China
• ²Jiangsu Provincial Medical Innovation Center, National Health Commission Key Laboratory of Enteric Pathogenic Microbiology, Jiangsu Provincial Center for Disease Control and Prevention, Nanjing, Liaoning Province, China
• ³Southeast University, Nanjing, Jiangsu Province, China
• ⁴National Institute for Communicable Disease Control and Prevention (China CDC), Beijing, China

Human brucellosis has re-emerged as a major public health threat in Jiangsu Province, but the sources and transmission dynamics of circulating strains remain poorly understood. In this study, we integrated conventional biotyping, whole-genome sequencing single-nucleotide polymorphism (WGS-SNP) analysis, and core genome multilocus sequence typing (cgMLST) to investigate the phylogenetic relationships of Brucella melitensis in the region. Among 89 isolates analyzed, all were confirmed as B. melitensis (16 as biovar 1 and 73 as biovar 3), with a widespread geographic distribution across 15 cities in Jiangsu and adjacent areas, indicating extensive regional dissemination. All strains belonged to sequence type 8 (ST8) and genotype group II, clustering within the East Mediterranean lineage. Genomic resolution classified these strains into five SNP clades (C-I to C-V) and 17 SNP-based genotypes (STs), revealing a ladder-like phylogenetic structure. The lack of distinct geographic clustering suggests frequent cross-regional transmission, likely facilitated by the movement of infected sheep and goats. Phylogenomic analysis through cgMLST revealed distinct clustering of the 17 STs into two major groups (G-I and G-II), with 15 STs (88.2%) showing high genetic concordance between Jiangsu isolates and strains from China's northeastern and northwestern. This compelling genomic evidence establishes that the current human brucellosis epidemic in Jiangsu is being driven by the nationwide expansion of dominant B. melitensis lineages. The findings provide crucial insights into the infection sources and interregional transmission dynamics of brucellosis in southern China, highlighting the significant role of domestic animal movement in pathogen dissemination, demanding coordinated crossregional interventions including strict implementing intervention strategies and enhance disease surveillance.