GD Animal Health Service, P.O. Box 9, 7400 AA Deventer, The Netherlands.
Vet Microbiol. 2012 Jan 27;154(3-4):272-81. doi: 10.1016/j.vetmic.2011.07.004. Epub 2011 Jul 14.
In many epidemiological models for paratuberculosis, it is assumed that infected young stock (<2 years of age) do not shed Mycobacterium avium subsp. paratuberculosis (MAP) before adulthood. If this assumption were true, the effective separation of young stock from adult cattle (≥ 2 years) would largely prevent postnatal infections, provided that uninfected adult cattle are highly resistant to infection. However, this assumption is in contrast with observed faecal shedding of MAP in young stock. Consequently, this assumption may have resulted in an underestimation of the effects of MAP transmission in herds participating in certification-, surveillance-, and control programmes for paratuberculosis. Therefore, the aim of the present study was to evaluate the long-term effects of transmission of MAP amongst young stock on key output parameters of certification-, surveillance-, and control programmes for paratuberculosis in simulated closed dairy herds. Closed Dutch dairy herds participating in a paratuberculosis programme were simulated with a stochastic model, JohneSSim. Various test schemes, preventive management measures, distributions of age at onset of faecal shedding and rates of effective contacts between young stock were simulated. The results indicate that transmission of MAP amongst young stock has no relevant effects on the animal-level prevalence and milk quality of herds that are certified in a paratuberculosis programme. However, transmission of MAP amongst young stock increased the economic losses due to paratuberculosis and costs of participation in a programme. Moreover, it substantially decreased the beneficial effect of the separation of young stock from adult cattle on the probability of being certified. However, even in the presence of transmission of MAP amongst young stock, preventive management measures to separate young stock from adult cattle remain important.
在许多副结核病的流行病学模型中，假设感染的幼畜（<2 岁）在成年之前不会排出鸟分枝杆菌副结核亚种（MAP）。如果这一假设成立，只要未感染的成年牛对感染具有高度抗性，那么将幼畜与成年牛（≥2 岁）有效隔离，将在很大程度上防止产后感染。然而，这一假设与观察到的幼畜中 MAP 的粪便排出情况相矛盾。因此，这一假设可能导致对参加副结核病认证、监测和控制计划的畜群中 MAP 传播的影响估计不足。因此，本研究的目的是评估 MAP 在幼畜中的传播对副结核病认证、监测和控制计划的关键输出参数的长期影响，在模拟的封闭奶牛畜群中进行研究。采用随机模型 JohneSSim 模拟了参加副结核病计划的封闭荷兰奶牛畜群。模拟了各种测试方案、预防性管理措施、粪便排出开始年龄的分布和幼畜之间有效接触的比率。结果表明，MAP 在幼畜中的传播对参加副结核病计划认证的畜群的动物水平流行率和牛奶质量没有相关影响。然而，MAP 在幼畜中的传播增加了由于副结核病导致的经济损失和参加计划的成本。此外，它大大降低了将幼畜与成年牛分离对认证概率的有益影响。然而，即使存在 MAP 在幼畜中的传播，将幼畜与成年牛分离的预防性管理措施仍然很重要。
