Data_Sheet_1_Identifying Edaphic Factors and Normalized Difference Vegetation Index Metrics Driving Wildlife Mortality From Anthrax in Kenya’s Wildlife Areas.xlsx

Anthrax, an acute disease of homeotherms caused by soil-borne Bacillus anthracis is implicated in dramatic declines in wildlife mainly in sub-Saharan Africa. Anthrax outbreaks are often localized in space and time. Therefore, understanding predictors of the spatial and temporal occurrence of anthrax in wildlife areas is useful in supporting early warning and improved response and targeting measures to reduce the impact of epizootic risk on populations. Spatial localization of anthrax is hypothesized to be driven by edaphic factors, while the temporal outbreaks are thought to be driven by extreme weather events including temperature, humidity, rainfall, and drought. Here, we test the role of select edaphic factors and normalized difference vegetation index (NDVI) metrics driven by vegetation structure and climate variability on the spatial and temporal patterns of wildlife mortality from anthrax in key wildlife areas in Kenya over a 20-year period, from 2000 to 2019. There was a positive association between the number of anthrax outbreaks and the total number of months anthrax was reported during the study period and the nitrogen and organic carbon content of the soil in each wildlife area. The monthly occurrence (timing) of anthrax in Lake Nakuru (with the most intense outbreaks) was positively related to the previous month’s spatial heterogeneity in NDVI and monthly NDVI deviation from 20-year monthly means. Generalized linear models revealed that the number of months anthrax was reported in a year (intensity) was positively related to spatial heterogeneity in NDVI, total organic carbon and cation exchange capacity of the soil. These results, examined in the light of experimental studies on anthrax persistence and amplification in the soil enlighten on mechanisms by which these factors are driving anthrax outbreaks and spatial localization.

炭疽（anthrax）是由土传炭疽芽孢杆菌（Bacillus anthracis）引发的恒温动物急性传染病，该病害主要在撒哈拉以南非洲地区造成野生动物种群的大幅衰退。炭疽暴发往往呈现空间与时间上的局域性特征。因此，明确野生动物栖息地内炭疽时空发生的预测因子，可为早期预警、优化应对策略及制定精准防控措施提供支撑，从而降低兽疫（epizootic）风险对野生动物种群的影响。学界普遍假设，炭疽的空间局域性由土壤因子（edaphic factors）驱动，而其时间尺度上的暴发则受气温、湿度、降雨与干旱等极端天气事件影响。本研究以2000至2019年这20年间肯尼亚重点野生动物栖息地内炭疽导致的野生动物死亡时空模式为研究对象，检验了筛选出的土壤因子以及由植被结构和气候变异性驱动的归一化差分植被指数（normalized difference vegetation index, NDVI）指标所起到的作用。研究期内，各野生动物栖息地的炭疽暴发次数、炭疽报告总月数，与当地土壤的氮含量及有机碳含量呈显著正相关。暴发强度最高的纳库鲁湖区域，其炭疽月度发生时间与上月NDVI空间异质性以及当月NDVI相较于20年月度均值的偏差呈显著正相关。广义线性模型（generalized linear models）结果显示，年度内炭疽报告月数（即暴发强度）与NDVI空间异质性、土壤总有机碳含量及阳离子交换量呈显著正相关。结合土壤中炭疽芽孢持久性与扩增的相关实验研究，本研究揭示了上述因子驱动炭疽暴发及其空间局域性的潜在机制。