Kirkeby Carsten, Græsbøll Kaare, Nielsen Søren Saxmose, Christiansen Lasse Engbo, Toft Nils, Halasa Tariq
DTU VET, Section for Epidemiology, Technical University of Denmark, Denmark.
Department of Large Animal Sciences, Section for Animal Welfare and Disease Control, University of Copenhagen, Denmark.
PLoS One. 2016 Dec 1;11(12):e0167219. doi: 10.1371/journal.pone.0167219. eCollection 2016.
Paratuberculosis is a chronic infection that in dairy cattle causes reduced milk yield, weight loss, and ultimately fatal diarrhea. Subclinical animals can excrete bacteria (Mycobacterium avium ssp. paratuberculosis, MAP) in feces and infect other animals. Farmers identify the infectious animals through a variety of test-strategies, but are challenged by the lack of perfect tests. Frequent testing increases the sensitivity but the costs of testing are a cause of concern for farmers. Here, we used a herd simulation model using milk ELISA tests to evaluate the epidemiological and economic consequences of continuously adapting the sampling interval in response to the estimated true prevalence in the herd. The key results were that the true prevalence was greatly affected by the hygiene level and to some extent by the test-frequency. Furthermore, the choice of prevalence that will be tolerated in a control scenario had a major impact on the true prevalence in the normal hygiene setting, but less so when the hygiene was poor. The net revenue is not greatly affected by the test-strategy, because of the general variation in net revenues between farms. An exception to this is the low hygiene herd, where frequent testing results in lower revenue. When we look at the probability of eradication, then it is correlated with the testing frequency and the target prevalence during the control phase. The probability of eradication is low in the low hygiene herd, and a test-and-cull strategy should probably not be the primary strategy in this herd. Based on this study we suggest that, in order to control MAP, the standard Danish dairy farm should use an adaptive strategy where a short sampling interval of three months is used when the estimated true prevalence is above 1%, and otherwise use a long sampling interval of one year.
副结核病是一种慢性感染病，在奶牛中会导致产奶量下降、体重减轻，并最终引发致命性腹泻。亚临床感染的动物可通过粪便排出细菌（副结核分枝杆菌，MAP），进而感染其他动物。养殖户通过多种检测策略来识别感染动物，但由于缺乏完美的检测方法而面临挑战。频繁检测可提高检测灵敏度，但检测成本是养殖户关注的一个问题。在此，我们使用了一个畜群模拟模型，结合牛奶ELISA检测，来评估根据畜群中估计的实际患病率不断调整采样间隔所产生的流行病学和经济后果。关键结果如下：实际患病率受卫生水平的影响很大，在一定程度上也受检测频率的影响。此外，在控制方案中可容忍的患病率选择，对正常卫生条件下的实际患病率有重大影响，但在卫生条件较差时影响较小。由于各养殖场净收益存在普遍差异，检测策略对净收益影响不大。低卫生水平畜群是个例外，频繁检测会导致收益降低。当我们考虑根除的可能性时，它与检测频率以及控制阶段的目标患病率相关。低卫生水平畜群根除的可能性较低，在该畜群中，检测并扑杀策略可能不应作为主要策略。基于本研究，我们建议，为了控制MAP，丹麦标准奶牛场应采用一种适应性策略，即当估计的实际患病率高于1%时，采用三个月的短采样间隔，否则采用一年的长采样间隔。
