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 (Odocoileus virginianus) 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 (Q) and assignment scores (A) for free‐ranging deer to wild populations were high (average Q_wild = 0.913 and average A_wild = 0.951, respectively), but varied among subregions (Q_wild = 0.800–0.947, A_wild = 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.

中文翻译：

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基因分配测试能否深入了解圈养外出对慢性消耗性疾病流行病学的影响？

确定正在发生的和新型疾病暴发的来源对于了解动物流行病的传播至关重要。当不同来源的个体之间几乎没有身体差异时，识别感染源就很困难。遗传分配程序在评估这种情况下的传播动态方面显示出巨大的前景。在这里，我们使用基因分配测试来确定自由放养的白尾鹿（ Odocoileus virginianus ）种群中慢性消耗性疾病感染的来源。自然传播被认为促进了慢性消耗性疾病的地理传播，但圈养鹿科动物种群的流出代表了另一种感染源，由于与野鹿的身体相似，因此很难检测到。根据在四个采样分区和五个圈养设施中收集的 1,912 个经验微卫星基因型的等位基因频率创建了模拟参考群体。这些参考种群用于评估 1,861 只自由放养的鹿（1,834 只未感染的鹿和 27 只感染的鹿）和 51 只圈养个体的祖先和分配到圈养或野生种群的可能性。自由放养的鹿对野生种群的祖先 ( Q ) 和分配分数 ( A ) 较高（分别为平均Q_野生 = 0.913 和平均A_野生 = 0.951），但在次区域之间存在差异（Q_野生 = 0.800–0.947，A_野生 = 0.857–0.976)。这些发现表明圈养逃逸和混合很少见，但风险在空间上可能并不均匀。在以前在自由放养鹿群中未观察到慢性消耗性疾病的地区采样的两只患有慢性消耗性疾病的自由放养鹿的祖先和分配分数表明，分配的可能性和归因于圈养种群的祖先比例较高。虽然我们不能直接将这些个体分配到受感染的设施，但这些发现表明，罕见的外出事件可能会影响自由放养人群中慢性消耗性疾病的流行病学。持续的疾病监测和遗传分析可能会进一步阐明圈养和野生来源的相对疾病风险。