Soil characteristics associated with historical commensal rodent plague foci in Yunnan Province, China.

BACKGROUND

Soil may influence pathogen persistence and outbreak dynamics, yet its characteristics and potential association with historical plague occurrence remain poorly understood. This study aimed to characterize the surface soil properties of three commensal rodent plague foci in Yunnan Province, China, and to explore their site-specific association with historical plague village status.

METHODS

From July to August 2019, 230 soil samples were collected from paired historical plague (n = 108) and non-plague (n = 122) villages in Mile, Mangshi, and Lianghe counties. Soil pH, soil electrical conductivity (SEC), soil organic matter (SOM), and seven metal elements (Fe, Ca, Ti, Co, Cu, Ni, V) were analyzed. Non-parametric tests, Spearman correlation, principal component analysis (PCA), and binary logistic regression were employed for data analysis.

RESULTS

The soils were overall acidic (median pH 5.82), slightly salinized (median SEC 166.51 μS/cm), with moderate SOM (median 21.14 g/kg). Concentrations of Fe, Ti, Co, Cu, Ni, and V significantly exceeded national background values (all p < 0.001). Pronounced regional differences (p < 0.001) were observed across the three sites: in Mile, soils were near-neutral (median pH 6.79), with the highest SEC (207.5 μS/cm) and the highest concentrations of Fe (91741.03 mg/kg), Cu (79.94 mg/kg), and V (310.1 mg/kg), but the lowest SOM (20.5 g/kg); in Mangshi, soils were acidic (median pH 5.57), with intermediate SEC (165.9 μS/cm) and metal levels, and moderate SOM (21.41 g/kg); in Lianghe (n = 71): Soils were the most acidic (median pH 5.48), with the lowest SEC (147.1 μS/cm) and lowest metal concentrations, but the highest SOM (22.05 g/kg). Post-hoc comparisons confirmed that Mile had significantly higher pH, SEC, Fe, Ti, Co, Cu, Ni, and V than both Mangshi and Lianghe (Bonferroni-corrected p < 0.017), while no significant differences in SOM were found across regions (p = 0.634). At the provincial level, historical plague villages had significantly lower Ni and V than non-plague villages (both p < 0.05), though regional sub-analyses showed that this pattern was not consistent across all foci, highlighting context-dependent variations. Multivariate analysis extracted four principal components (cumulative variance: 83.72%). Multivariate logistic regression suggested that the heavy metal-rich principal component (PC1) was independently associated with reduced likelihood of historical plague village classification, while loam texture was associated with lower odds of historical plague occurrence relative to sandy soil.

CONCLUSION

Soils in the three plague foci are acidic, slightly saline, and enriched in several metals, with properties varying significantly by region. In this exploratory, cross-sectional analysis, a multivariate soil profile dominated by heavy metals and loam texture showed a statistical association with historical plague occurrence. These site-specific findings provide crucial baseline data and a multivariate analytical framework for future investigations into the complex, and likely context-dependent, relationships between soil environments and plague ecology.