Analysis of the Effects of Hydrometeorological Conditions on Flea Indices of Two Rodent Species in Inner Mongolia.

Climate change has modified hydrometeorological patterns, influencing plague transmission risks in Inner Mongolia. Using 2013-2021 plague surveillance data from 12 regions in Inner Mongolia, we assessed drought and wet conditions' effects on flea parasitism in two key rodents: Mongolian gerbil (Meriones unguiculatus) and Daurian ground squirrel (Spermophilus dauricus). Extreme gradient boosting (XGBoost) modeling revealed the Standardized Precipitation Evapotranspiration Index (SPEI), maximum ground surface temperature, average relative humidity, average sunshine duration, and maximum wind speed collectively explained 52.60% of generalized flea index variation (SPEI contribution: 14.13%). Distributed lag non-linear model (DLNM) analysis revealed that drought conditions cumulatively increased generalized flea indices, particularly moderate drought (SPEI = -1.8), which showed a significant lagged effect on generalized flea indices after 3 months (RR = 2.76, 95% CI: 1.78-4.27). Conversely, the cumulative effects of wet conditions were detrimental to the increase in generalized flea indices. In addition to exhibiting the generalized flea index characteristics under drought conditions, the plague vectors Nosopsyllus laeviceps and Xenopsylla conformis parasitic on M. unguiculatus showed a facilitative effect in the 3rd month following severe wet conditions, with effect sizes of relative risk (RR) = 1.97 (95% CI: 1.13-3.45) and RR = 5.96 (95% CI: 3.25-10.94), respectively. With increasing drought severity, the flea index of M. unguiculatus rose significantly after a 3-month lag, with Z-test statistics of 2.16 (SPEI_3 = -1) and 2.63 (SPEI_3 = -1.5), both p < 0.05. Under severe drought (SPEI_3 = -1.5), the cumulative RR showed a significant difference in the two rodent species (Z = 2.27, p < 0.05). Therefore, it is essential to proactively monitor drought conditions in Inner Mongolia, particularly during the 3 months following a drought, and special attention should be paid to the increased abundance of Nosopsyllus laeviceps and Xenopsylla conformis in the 3rd month following severe wet conditions.