Reconstructing the emergence of a lethal infectious disease of wildlife supports a key role for spread through translocations by humans

There have been few reconstructions of wildlife disease emergences, despite their extensive impact on biodiversity and human health. This is in large part attributable to the lack of structured and robust spatio-temporal datasets. We overcame logistical problems of obtaining suitable information by using data from a citizen science project and formulating spatio-temporal models of the spread of a wildlife pathogen (genus Ranavirus, infecting amphibians). We evaluated three main hypotheses for the rapid increase in disease reports in the UK: that outbreaks were being reported more frequently, that climate change had altered the interaction between hosts and a previously widespread pathogen, and that disease was emerging due to spatial spread of a novel pathogen. Our analysis characterized localized spread from nearby ponds, consistent with amphibian dispersal, but also revealed a highly significant trend for elevated rates of additional outbreaks in localities with higher human population density—pointing to human activities in also spreading the virus. Phylogenetic analyses of pathogen genomes support the inference of at least two independent introductions into the UK. Together these results point strongly to humans repeatedly translocating ranaviruses into the UK from other countries and between UK ponds, and therefore suggest potential control measures.

尽管野生动物疾病暴发事件对生物多样性与人类健康造成了广泛影响，但目前针对其暴发过程的重建研究仍较为匮乏。这一现状在很大程度上可归因于缺乏结构化且可靠的时空数据集。本研究借助公民科学（citizen science）项目获取的相关数据，构建了感染两栖动物的蛙病毒属（Ranavirus）野生动物病原体传播的时空模型，解决了获取适宜研究信息的后勤难题。针对英国地区疾病报告数量快速增长的现象，我们评估了三项核心假说：一是疾病暴发的报告频率有所提升；二是气候变化改变了宿主与此前广泛流行的病原体之间的相互作用；三是新型病原体的空间传播导致了疾病的暴发。我们的分析结果显示，病毒存在从邻近池塘扩散的局域传播特征，这与两栖动物的自然扩散模式相符；同时还发现，在人口密度更高的区域，新增暴发事件的发生率呈极为显著的上升趋势——这提示人类活动同样推动了病毒的传播。对病原体基因组的系统发育分析支持了病毒至少有两次独立传入英国的推断。综合来看，这些结果强有力地表明，人类反复将蛙病毒从其他国家传入英国，或是在英国境内的池塘之间进行跨区域转移，因此本研究提出了相应的潜在防控措施。