Zoonotic Barrier Disruption and the Rise of the Third Plague Pandemic: A One Health Analysis of 19th-Century Yunnan and the Emergence of Yersinia pestis Strain 1.ORI

The Third Plague Pandemic originated in 19th-century Yunnan, China, yet the confluence of factors that enabled the pandemic strain Yersinia pestis 1.ORI to emerge and spread globally remains unclear. Using a One Health framework, this study investigates how human-driven ecological and socioeconomic changes disrupted zoonotic barriers in Yunnan. We conduct an interdisciplinary historical analysis, triangulating evidence from Qing dynasty gazetteers, environmental reconstructions, and biological data on plague ecology, including host–vector dynamics, to model conditions for spillover and spread and to build a convergent, validated case. The analysis identifies a mid-19th-century convergence that created a high-risk interface: widespread deforestation from mining and agriculture, rapid population growth, increased synanthropic rat densities, and the turmoil of the Panthay Rebellion. Socioeconomic stressors—labour migration into mining valleys, currency devaluation undermining food security, and comorbidities such as malnutrition, heavy metal contamination, and opium use—may have further increased host susceptibility. This socio-ecological context catalysed spillover and establishment of the 1.ORI strain in commensal rat populations. The findings show the pandemic’s origin reflects spatiotemporal convergence rather than a single cause, while noting uncertainty in quantifying historical ecological and health parameters; the case offers a framework for assessing contemporary pandemic risks. It underscores how layered pressures operate across timescales.