Widgren Stefan, Frössling Jenny
Department of Disease Control and Epidemiology, National Veterinary Institute, Uppsala, Sweden.
Geospat Health. 2010 Nov;5(1):119-30. doi: 10.4081/gh.2010.192.
Understanding the intensity and spatial patterns of animal transfers is of prime importance as geographical moves play an important part in the spread and potential control of contagious animal diseases of veterinary importance. For the purpose of visualizing all registered between-herd animal movements in Sweden between 1 July 2005 and 31 December 2008 by map animation, a grid network technique based on the Bresenham line algorithm was developed. Potential spatio-temporal clustering of animals registered as sold or purchased based on location and month of trade was also detected and tested using a spatial scan statistic. Calculations were based on data from 31,375 holdings and 3,487,426 head of cattle. In total, 988,167 between-herd movements of individual bovines were displayed in a sequence of maps covering three and a half years by 2-week intervals. The maps showed that several cattle movements, both short- and long-distance, take place in Sweden each week of the year. However, most animals (75%) were only registered at one single holding during the study period and 23% were sold to a different holding once. Spatial scan statistics based on data from the year 2008 indicated uneven distributions of purchased or sold animals in space and time. During each autumn, there was an increase in cattle movements and October and November showed significantly more cases of sold or purchased animals (relative risk ~1.7, p = 0.001). Based on the results, we conclude that cattle trade is constantly active at a considerable level. This, in combination with possibly insufficient biosecurity routines applied on many farms, constitutes a risk that contagious diseases are spread in the population. The grid network maps were generated through the use of open-source tools and software in order to decrease software costs and facilitate sharing of programme code. In addition, the technique was based on scripts that allow for the inclusion of iterative processes and that comprise all main parts of map creation. Thereby, a large number of maps can be generated and the demands for high reproducibility are met.
了解动物转移的强度和空间模式至关重要，因为地理迁移在具有兽医重要性的传染性动物疾病的传播及潜在控制中起着重要作用。为了通过地图动画可视化2005年7月1日至2008年12月31日瑞典所有登记的 herd 间动物移动情况，开发了一种基于布雷森汉姆线算法的网格网络技术。还使用空间扫描统计方法检测并测试了基于交易地点和月份登记为出售或购买的动物的潜在时空聚集情况。计算基于来自31375个养殖场和3487426头牛的数据。总共988167次个体牛的 herd 间移动在一系列以两周为间隔、涵盖三年半的地图中展示。地图显示，瑞典每年的每周都有几次牛的短距离和长距离移动。然而，在研究期间，大多数动物（75%）仅在一个养殖场登记，23%的动物只被出售到另一个养殖场一次。基于2008年数据的空间扫描统计表明，购买或出售动物在空间和时间上分布不均。每年秋季，牛的移动都会增加，10月和11月出售或购买动物的情况明显更多（相对风险约为1.7，p = 0.001）。基于这些结果，我们得出结论，牛的贸易在相当程度上持续活跃。这与许多农场可能应用不足的生物安全程序相结合，构成了传染病在牛群中传播的风险。网格网络地图是通过使用开源工具和软件生成的，以降低软件成本并便于程序代码的共享。此外，该技术基于允许包含迭代过程且涵盖地图创建所有主要部分的脚本。因此，可以生成大量地图并满足高再现性的要求。 （注：原文中“herd”可能有更准确的畜牧相关专业术语含义，这里暂按常见意思翻译为“畜群、牧群”，但可能需要结合专业背景进一步准确理解。）
