Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Prev Vet Med. 2013 Jul 1;110(3-4):335-45. doi: 10.1016/j.prevetmed.2013.01.006. Epub 2013 Feb 16.
Paratuberculosis, or Johne's disease (JD), is a chronic enteric disease of ruminants infected by Mycobacterium avium subsp. paratuberculosis (MAP) that causes a significant financial loss in dairy industry. To reduce prevalence and transmission in dairy herds infected with MAP, control programs have been implemented, including test-based culling, improved calf rearing management, and vaccination. The important issue of preventing MAP invasion into a MAP-free herd has been less investigated, however. The objective of this study was to examine whether vaccination was able to prevent MAP invasion in dairy cattle using a stochastic simulation approach. We developed a MAP vaccination model in which calves were vaccinated with a vaccine that is both imperfect in reducing the susceptibility of the host ('leaky') and that does not successfully immunize all calves ('failure in take'). Probability of MAP persistence and the number of infected animals in herds were computed for both control and vaccinated herds over a ten-year period after introduction of an initial infected heifer. Global parameter sensitivity analyses were performed to find the most influential parameters for MAP invasion. Our results show that vaccination of calves is effective in preventing MAP invasion, provided that the vaccine is of high efficacy in both reduction of susceptibility and 'take' effects; however, there is still a small chance (<0.15) that MAP can be sustained in herds over a long time (>10 years) due to vertical transmission. This study indicates that reduction in the transmission rate of high shedders (>50 CFU), the number of infected heifers initially introduced to herds, and vertical transmission are important to further decrease the probability of MAP becoming endemic and the overall number of infected animals in endemic herds. The simulation work is useful for designing vaccination programs aimed at preventing MAP invasion in MAP-free herds.
副结核病，又称约翰氏病（JD），是一种由牛分枝杆菌副结核亚种（MAP）感染反刍动物引起的慢性肠病，给奶牛养殖业造成了巨大的经济损失。为了降低感染 MAP 的奶牛群中的流行率和传播率，已经实施了控制计划，包括基于检测的淘汰、改善犊牛饲养管理和疫苗接种。然而，防止 MAP 侵入无 MAP 牛群的重要问题研究较少。本研究旨在通过随机模拟方法研究疫苗接种是否能够防止 MAP 侵入奶牛。我们开发了一种 MAP 疫苗接种模型，其中犊牛接种一种疫苗，该疫苗在降低宿主易感性方面存在缺陷（“渗漏”），并且不能成功免疫所有犊牛（“接种失败”）。在引入初始感染的小母牛后的十年内，为对照和接种牛群计算了 MAP 持续存在的概率和牛群中感染动物的数量。进行了全局参数敏感性分析，以找到影响 MAP 入侵的最主要参数。研究结果表明，只要疫苗在降低易感性和“接种”效果方面具有高功效，对犊牛进行疫苗接种就能有效预防 MAP 入侵；然而，由于垂直传播，MAP 在牛群中持续存在很长时间（> 10 年）的可能性仍然很小（<0.15）。本研究表明，降低高排毒量（> 50 CFU）的传播率、最初引入牛群的感染小母牛数量以及垂直传播，对于进一步降低 MAP 地方性流行的概率和地方性流行牛群中感染动物的总数非常重要。模拟工作对于设计旨在防止 MAP 侵入无 MAP 牛群的疫苗接种计划非常有用。
