Pepin Kim M, Davis Amy J, Streicker Daniel G, Fischer Justin W, VerCauteren Kurt C, Gilbert Amy T
National Wildlife Research Center, United States Department of Agriculture, Wildlife Services, Fort Collins, Colorado, United States of America.
Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, Scotland.
PLoS Negl Trop Dis. 2017 Jul 31;11(7):e0005822. doi: 10.1371/journal.pntd.0005822. eCollection 2017 Jul.
Prevention and control of wildlife disease invasions relies on the ability to predict spatio-temporal dynamics and understand the role of factors driving spread rates, such as seasonality and transmission distance. Passive disease surveillance (i.e., case reports by public) is a common method of monitoring emergence of wildlife diseases, but can be challenging to interpret due to spatial biases and limitations in data quantity and quality.
METHODOLOGY/PRINCIPAL FINDINGS: We obtained passive rabies surveillance data from dead striped skunks (Mephitis mephitis) in an epizootic in northern Colorado, USA. We developed a dynamic patch-occupancy model which predicts spatio-temporal spreading while accounting for heterogeneous sampling. We estimated the distance travelled per transmission event, direction of invasion, rate of spatial spread, and effects of infection density and season. We also estimated mean transmission distance and rates of spatial spread using a phylogeographic approach on a subsample of viral sequences from the same epizootic. Both the occupancy and phylogeographic approaches predicted similar rates of spatio-temporal spread. Estimated mean transmission distances were 2.3 km (95% Highest Posterior Density (HPD95): 0.02, 11.9; phylogeographic) and 3.9 km (95% credible intervals (CI95): 1.4, 11.3; occupancy). Estimated rates of spatial spread in km/year were: 29.8 (HPD95: 20.8, 39.8; phylogeographic, branch velocity, homogenous model), 22.6 (HPD95: 15.3, 29.7; phylogeographic, diffusion rate, homogenous model) and 21.1 (CI95: 16.7, 25.5; occupancy). Initial colonization probability was twice as high in spring relative to fall.
CONCLUSIONS/SIGNIFICANCE: Skunk-to-skunk transmission was primarily local (< 4 km) suggesting that if interventions were needed, they could be applied at the wave front. Slower viral invasions of skunk rabies in western USA compared to a similar epizootic in raccoons in the eastern USA implies host species or landscape factors underlie the dynamics of rabies invasions. Our framework provides a straightforward method for estimating rates of spatial spread of wildlife diseases.
野生动物疾病入侵的预防与控制依赖于预测时空动态以及理解驱动传播速率的因素（如季节性和传播距离）所起的作用。被动疾病监测（即公众上报病例）是监测野生动物疾病出现的常用方法，但由于空间偏差以及数据数量和质量方面的局限性，其解读可能具有挑战性。
方法/主要发现：我们获取了美国科罗拉多州北部一次狂犬病流行中死亡带纹臭鼬（Mephitis mephitis）的被动监测数据。我们开发了一个动态斑块占用模型，该模型在考虑异质采样的情况下预测时空传播。我们估计了每次传播事件的传播距离、入侵方向、空间传播速率以及感染密度和季节的影响。我们还对来自同一次疫情的病毒序列子样本采用系统发育地理学方法估计了平均传播距离和空间传播速率。占用模型和系统发育地理学方法预测的时空传播速率相似。估计的平均传播距离分别为2.3千米（95%最高后验密度（HPD95）：0.02，11.9；系统发育地理学方法）和3.9千米（95%可信区间（CI95）：1.4，11.3；占用模型）。估计的空间传播速率（千米/年）分别为：29.8（HPD95：20.8，39.8；系统发育地理学方法，分支速度，同质模型）、22.6（HPD95：15.3，29.7；系统发育地理学方法，扩散速率，同质模型）和21.1（CI95：16.7，25.5；占用模型）。春季的初始定殖概率相对于秋季高出两倍。
结论/意义：臭鼬间传播主要是局部性的（<4千米），这表明如果需要采取干预措施，可以在波前实施。与美国东部浣熊的类似疫情相比，美国西部臭鼬狂犬病的病毒入侵速度较慢，这意味着宿主物种或景观因素是狂犬病入侵动态的基础。我们的框架提供了一种估算野生动物疾病空间传播速率的直接方法。
