INRA, ONIRIS, UMR1300 Bioagression, Epidémiologie et Analyse de Risque, BP 40706, F-44307 Nantes, France.
Prev Vet Med. 2011 Jun 15;100(2):116-25. doi: 10.1016/j.prevetmed.2011.02.004. Epub 2011 May 6.
Within-herd transmission of pathogens occurs either by direct or by indirect contact between susceptible and infected animals. In dairy herds that are structured into groups, the way in which animals encounter each other and share an environment can affect pathogen transmission. Dairy cattle are heterogeneous in terms of susceptibility and infectivity with respect to Mycobacterium avium subspecies paratuberculosis (Map) transmission. It is mainly young animals that are susceptible and adults that are infectious. Both vertical and horizontal transmission through the ingestion of Map shed into the environment by adults and transiently infected calves can occur. Our objective was to assess the effect of contact structure on Map transmission in persistently infected dairy herds and to examine the effect of isolating calves from other calves or from adults before weaning. We developed a stochastic compartmental model of Map transmission in a closed dairy herd. The model reflects the Map infection process and herd management characteristics. Indirect transmission via the environment was modelled explicitly. Six infection states (susceptible, resistant, transiently infectious, latently infected, subclinically infected, and clinically affected) and two contaminated farm area environments (whole farm and calf area) were modelled. Calves were housed in hutches, individual indoor pens, or group indoor pens. Two different levels of exposure of calves to a farm environment contaminated by adults were possible: no exposure and indirect exposure through fomites. Three herd sizes were studied. We found that contacts between calves before weaning did not influence Map transmission in a herd, whereas the level of exposure of calves to an environment contaminated by adults and the starting age of exposure of calves to adults were pivotal. Early culling of clinically affected adults led to a lower prevalence of infectious adults over time. The results were independent of herd size. Despite the many transmission routes that are known, the best control approach is to limit the exposure of calves to adult faeces through the systematic separation of adults and calves in combination with hygiene measures. Reducing contact between calves does not appear effective.
在具有不同易感性和感染性的奶牛中，分枝杆菌副结核病（Map）的传播是不均匀的。在分组的奶牛群中，动物相互接触和共享环境的方式会影响病原体的传播。在牛群中，主要是幼畜易感，而成畜具有传染性。成畜通过环境传播和幼畜通过垂直传播和水平传播都可能发生，而水平传播是通过摄入成畜和暂时感染的小牛排泄到环境中的 Map 实现的。我们的目标是评估接触结构对持续感染的奶牛群中 Map 传播的影响，并研究在小牛断奶前将其与其他小牛或成畜隔离的效果。我们开发了一个封闭奶牛场中 Map 传播的随机隔间模型。该模型反映了 Map 感染过程和牛群管理特征。环境中的间接传播被明确建模。有六个感染状态（易感、抗性、暂时感染、潜伏感染、亚临床感染和临床感染）和两个受污染的农场区域环境（整个农场和小牛区）。小牛被安置在畜舍、单独的室内畜栏或群体室内畜栏中。小牛有两种不同程度的接触受成畜污染的农场环境：无接触和通过污染物的间接接触。研究了三种不同的牛群规模。我们发现，在断奶前，小牛之间的接触并不影响牛群中的 Map 传播，而小牛接触受成畜污染的环境的程度以及小牛接触成畜的起始年龄则是关键因素。及早淘汰临床感染的成畜会导致感染成畜的流行率随着时间的推移而降低。结果与牛群规模无关。尽管有许多已知的传播途径，但最好的控制方法是通过系统地将成畜和小牛分开，并结合卫生措施，限制小牛接触成畜的粪便。减少小牛之间的接触似乎没有效果。
