Kirkeby Carsten, Græsbøll Kaare, Nielsen Søren Saxmose, Toft Nils, Halasa Tariq
National Veterinary Institute, Technical University of Denmark, Kemitorvet, bygning 204, 2800, Kgs. Lyngby, Denmark.
DTU Compute, Section for Dynamical Systems, Department of Applied Mathematics and Computer Science, Technical University of Denmark, Richard Petersens Plads, Bygning 324, 2800, Kgs. Lyngby, Denmark.
BMC Vet Res. 2017 Jun 27;13(1):202. doi: 10.1186/s12917-017-1119-z.
Paratuberculosis (PTB) is a chronic disease which may lead to reduced milk yield, lower animal welfare and death in cattle. The causative agent is Mycobacterium avium subsp. paratuberculosis (MAP). The economic consequences are particularly important incentives in the control and eradication of the infection. One strategy to control PTB in a herd is to purchase animals from farms with a low risk of MAP infection. We wanted to investigate the epidemiological and economic consequences of buying livestock from different supplier farms of low, medium or high risk, as well as farms with unknown status. We also wanted to estimate the probability of spontaneous fadeout if the farmer of an initially MAP-free herd bought a specified number of infected animals in a single year, or continually bought infected animals. This was achieved through simulation modeling, and the effects of consistently introducing one, five or ten infected animals annually into an initially infection-free herd was also modeled.
Our findings show that once infected, a farm can relatively safely purchase animals from other low and medium-risk farms without experiencing an increase in the prevalence, highlighting the importance of certification programmes. Furthermore, farms free of MAP are highly susceptible and cannot purchase more than a small number of animals per year without having a high risk of being infected. The probability of spontaneous fadeout after 10 years was 82% when introducing a single infected animal into an initially MAP-free herd. When purchasing ten infected animals, this probability was 46%. The continual purchase of infected animals resulted in very low probabilities of spontaneous fadeout.
We demonstrated that MAP-free farms can purchase a small number of animals, preferably from certified farms, each year and still remain free of MAP. Already infected farms have little risk of increasing the prevalence on a farm when purchasing animals from other farms.
副结核病（PTB）是一种慢性疾病，可能导致奶牛产奶量下降、动物福利降低以及死亡。病原体是鸟分枝杆菌副结核亚种（MAP）。经济后果是控制和根除该感染的特别重要的诱因。控制畜群中PTB的一种策略是从MAP感染风险低的农场购买动物。我们想调查从低、中、高风险的不同供应商农场以及状况不明的农场购买牲畜的流行病学和经济后果。我们还想估计，如果最初无MAP的畜群的农场主在一年内购买特定数量的感染动物，或持续购买感染动物，自发消退的概率。这是通过模拟建模实现的，还对每年持续引入1头、5头或10头感染动物到最初无感染的畜群中的影响进行了建模。
我们的研究结果表明，一旦感染，一个农场可以相对安全地从其他低风险和中等风险农场购买动物，而不会出现患病率增加的情况，这突出了认证计划的重要性。此外，无MAP的农场高度易感，如果每年购买的动物数量超过少量，就有很高的感染风险。当将1头感染动物引入最初无MAP的畜群时，10年后自发消退的概率为82%。购买10头感染动物时，这个概率为46%。持续购买感染动物导致自发消退的概率非常低。
我们证明，无MAP的农场每年可以购买少量动物，最好是从经过认证的农场购买，并且仍然可以保持无MAP状态。已经感染的农场从其他农场购买动物时，增加农场患病率的风险很小。
