Miller William L, Walter W David
Pennsylvania Cooperative Fish and Wildlife Research Unit Department of Ecosystem Science and Management Intercollege Graduate Degree Program in Ecology The Pennsylvania State University University Park PA USA.
U.S. Geological Survey Pennsylvania Cooperative Fish and Wildlife Research Unit The Pennsylvania State University University Park PA USA.
Evol Appl. 2019 Dec 9;13(4):715-726. doi: 10.1111/eva.12895. eCollection 2020 Apr.
Identifying the sources of ongoing and novel disease outbreaks is critical for understanding the diffusion of epizootic diseases. Identifying infection sources is difficult when few physical differences separate individuals with different origins. Genetic assignment procedures show great promise for assessing transmission dynamics in such situations. Here, we use genetic assignment tests to determine the source of chronic wasting disease infections in free-ranging white-tailed deer () populations. Natural dispersal is thought to facilitate the geographic diffusion of chronic wasting disease, but egression from captive cervid populations represents an alternative source of infection that is difficult to detect due to physical similarities with wild deer. Simulated reference populations were created based on allele frequencies from 1,912 empirical microsatellite genotypes collected in four sampling subregions and five captive facilities. These reference populations were used to assess the likelihood of ancestry and assignment of 1,861 free-ranging deer (1,834 noninfected and 27 infected) and 51 captive individuals to captive or wild populations. The ancestry () and assignment scores () for free-ranging deer to wild populations were high (average = 0.913 and average = 0.951, respectively), but varied among subregions ( = 0.800-0.947, = 0.857-0.976). These findings suggest that captive egression and admixture are rare, but risk may not be spatially uniform. Ancestry and assignment scores for two free-ranging deer with chronic wasting disease sampled in an area where chronic wasting disease was previously unobserved in free-ranging herds indicated a higher likelihood of assignment and proportion of ancestry attributable to captive populations. While we cannot directly assign these individuals to infected facilities, these findings suggest that rare egression events may influence the epizootiology of chronic wasting disease in free-ranging populations. Continued disease surveillance and genetic analyses may further elucidate the relative disease risk attributable to captive and wild sources.
识别正在发生的和新出现的疾病爆发源对于理解动物流行病的传播至关重要。当不同来源的个体在生理上差异很小时，识别感染源就很困难。基因分配程序在评估这种情况下的传播动态方面显示出巨大潜力。在这里，我们使用基因分配测试来确定自由放养的白尾鹿种群中慢性消耗病感染的来源。自然扩散被认为有助于慢性消耗病的地理传播，但圈养鹿群的逸出是另一种感染源，由于与野生鹿在生理上相似，很难检测到。基于在四个采样子区域和五个圈养设施中收集的1912个经验性微卫星基因型的等位基因频率创建了模拟参考种群。这些参考种群用于评估1861只自由放养的鹿（1834只未感染和27只感染）和51只圈养个体属于圈养或野生种群的祖先可能性和分配情况。自由放养的鹿到野生种群的祖先系数（）和分配分数（）很高（平均分别为0.913和0.951），但在各子区域之间有所不同（=0.800 - 0.947，=0.857 - 0.976）。这些发现表明圈养逸出和混合很少见，但风险在空间上可能并不均匀。在一个自由放养鹿群中以前未观察到慢性消耗病的地区采样的两只患有慢性消耗病的自由放养鹿的祖先系数和分配分数表明，其被分配到圈养种群的可能性和祖先比例更高。虽然我们不能直接将这些个体与受感染的设施联系起来，但这些发现表明罕见的逸出事件可能会影响自由放养育种群中慢性消耗病的流行病学。持续的疾病监测和基因分析可能会进一步阐明圈养和野生来源所带来的相对疾病风险。
