Spatiotemporal dynamics and serosurveillance landscape of brucellosis at the human-animal interface in the Chinese Southwest: A retrospective study

INTRODUCTION: Human brucellosis is re-emerging in the Chinese Southwest, and its epidemic characteristics remain unclear. METHODOLOGY: Descriptive epidemiology, Joinpoint regression, spatial autocorrelation, serological surveillance and pathogen analysis were adopted to clarify the epidemiological evolution of the disease. RESULTS: Between 2004 and 2024, 9,822 brucellosis cases occurred, dominated by 7,270 cases in Yunnan. The epidemic showed a persistent upward trend (AAPC = +3.5%, P < 0.05), and identified a critical rebound after 2018 (APC = +3.5%, P < 0.05). Serological surveillance of 36,459 individuals revealed a seropositivity rate of 2.13% (95%CI, 2.00%, 2.26%), identifying 1,831 new cases. Sheep/goats seropositivity at 1.02% ((95%CI, 0.97%, 1.06%) and cattle at 0.45% (95%CI, 0.42%, 0.48%). Sustained elevated human incidence was validated by serological evidence, and seroprevalence trends in sheep/goats aligned closely with human epidemic dynamics. Human brucellosis has evolved from random to significantly geographically and spatial aggregated, spreading continuously with intensified clustering in central-eastern Yunnan, the Sichuan basin and Tibet's Ngari-Qamdo axis, highlighting these as priority control zones. Human brucellosis has transitioned from sporadic to locally endemic, with phased progression and increasing geographical clustering recently. Human brucellosis in the Chinese Southwest is characterized by the persistent dominance of B. melitensis bv. 3, primarily represented by the co-circulating MLVA-11 genotypes GT116 and GT125, which form a stable, widely disseminated lineage across the region. CONCLUSION: From the re-emergence to persistent endemicity of human brucellosis in study area, the extensive distribution of B. melitensis with unique genotyping reveals a stable zoonotic cycle that requires coordinated regional control.