Graham D A, Clegg T A, Thulke H-H, O'Sullivan P, McGrath G, More S J
Animal Health Ireland, Main St, Carrick on Shannon, Co. Leitrim, Ireland.
UCD Centre for Veterinary Epidemiology and Risk Analysis, UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
Prev Vet Med. 2016 Apr 1;126:30-8. doi: 10.1016/j.prevetmed.2016.01.017. Epub 2016 Jan 21.
The control of bovine viral diarrhoea virus (BVDV) mainly focuses on the identification and restriction of persistently infected (PI) animals. However, other transmission pathways can also result in new breakdowns, including the movement of animals pregnant with PI calves (Trojan animals) and the spread of infection between contiguous farms. Contiguous spread is likely an important problem in the BVD eradication programme in Ireland, given the spatial distribution of residual infection, and the highly fragmented nature of land holdings on many Irish farms. In this study, we seek to quantify the risk of BVD spread between contiguous herds in Ireland. Multivariable logistic models were used to estimate the risk of a herd having BVD positive calves in January to June 2014 (the study period) when contiguous to a herd that had at least one BVD positive calf born in 2013. The models included risk factors relating to the study herd and to neighbouring herds. Separate multivariable models were built for each of four "PI-neighbour" factors relating to the presence of BVD+ animals and/or the presence of offspring of PI breeding animals. In total, 58,483 study herds were enrolled. The final model contained the province, the log of the number of calf births born during the study period, the number of cattle purchased between January 2013 and January 2014, and with a two-way interaction between the number of animals of unknown BVD status in the study herd and the PI-neighbour risk factor. When the number of PI-neighbour herds was used as the PI-neighbour risk factor, the odds ratio (OR) associated with the number of PI-neighbour herds ranged from 1.07 to 3.02, depending on the number of unknown animals present. To further explore the risk associated with PI-neighbour factors, the models were repeated using a subset of the study herds (n=7440) that contained no animals of unknown status. The best fitting model including "any PI-neighbour" as the PI-neighbour factor and also contained the log of the number of calf births born during the study period and the number of cattle purchased. The OR associated with "any PI-neighbour" was 1.92 (95% C.I. 1.37-2.70). This study provides the first quantitative information on the risks posed by the presence of BVD+ animals in neighbouring herds and also highlights the importance of clarifying the BVD status of animals that have not yet been tested in the context of the Irish eradication programme.
牛病毒性腹泻病毒（BVDV）的防控主要集中在识别和限制持续感染（PI）动物。然而，其他传播途径也可能导致新的疫情爆发，包括怀有PI犊牛的动物（特洛伊木马动物）的移动以及相邻农场之间的感染传播。鉴于残留感染的空间分布以及爱尔兰许多农场土地持有高度分散的性质，相邻传播在爱尔兰的BVD根除计划中可能是一个重要问题。在本研究中，我们试图量化爱尔兰相邻畜群间BVD传播的风险。使用多变量逻辑模型来估计在2014年1月至6月（研究期）期间，当一个畜群与在2013年出生至少一头BVD阳性犊牛的畜群相邻时，该畜群出现BVD阳性犊牛的风险。这些模型纳入了与研究畜群和相邻畜群相关的风险因素。针对与BVD+动物的存在和/或PI繁殖动物后代的存在相关的四个“PI邻群”因素分别构建了单独的多变量模型。总共纳入了58483个研究畜群。最终模型包含省份、研究期内犊牛出生数量的对数、2013年1月至2014年1月期间购买的牛的数量，以及研究畜群中BVD状态未知的动物数量与PI邻群风险因素之间的双向交互作用。当将PI邻群的数量用作PI邻群风险因素时，与PI邻群数量相关的优势比（OR）范围为1.07至3.02，具体取决于未知动物的数量。为了进一步探究与PI邻群因素相关的风险，使用研究畜群的一个子集（n = 7440）重复这些模型，该子集中不包含状态未知的动物。最佳拟合模型将“任何PI邻群”作为PI邻群因素，并且还包含研究期内犊牛出生数量的对数和购买的牛的数量。与“任何PI邻群”相关的OR为1.92（95%置信区间1.37 - 2.70）。本研究提供了关于相邻畜群中存在BVD+动物所带来风险的首个定量信息，同时也凸显了在爱尔兰根除计划背景下明确尚未检测动物的BVD状态的重要性。
