Johne's disease (JD) is a chronic enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), with control primarily aimed at preventing new infections among calves. The aim of the current study was to quantify calf-to-calf transmission of MAP among penmates in an experimental trial. Newborn Holstein bull calves (n = 32) were allocated into pens of 4, with 2 inoculated (IN) calves and 2 calves that were contact exposed (CE). Calves were group-housed for 3 months, with frequent collection of fecal and blood samples and tissue collection after euthanasia. The basic reproduction ratio (R0) was estimated using a final size (FS) model with a susceptible-infected model, based on INF-γ ELISA and tissue culture followed by qPCR. In addition, the transmission rate parameter (β) for new shedding events was estimated using a general linearized method (GLM) model with a susceptible-infected-susceptible model based on culture, followed by qPCR, of fecal samples collected during group housing. The R0 was derived for IN and CE calves separately, due to a difference in susceptibility, as well as differences in duration of shedding events. Based on the FS model, interferon-γ results from blood samples resulted in a R 0 IG of 0.90 (0.24, 2.59) and tissue culture resulted in a R 0 T of 1.36 (0.45, 3.94). Based on the GLM model, the R0 for CE calves to begin shedding (R 0 CE ) was 3.24 (1.14, 7.41). We concluded that transmission of MAP infection between penmates occurred and that transmission among calves may be an important cause of persistent MAP infection on dairy farms that is currently uncontrolled for in current JD control programs.

中文翻译：

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量化鸟分枝杆菌亚种的传播。集体饲养的奶牛犊中的副结核病。

约翰尼氏病（JD）是由鸟分枝杆菌亚种引起的慢性肠炎。副结核病（MAP），其控制主要旨在预防小牛之间的新感染。本研究的目的是在一项实验性试验中量化MAP在小伙伴之间的小腿到小腿之间的传播。将新生的荷斯坦公牛犊（n = 32）分成4只圈，其中2头接种（IN）犊牛和2头接触暴露（CE）犊牛。小牛分组饲养三个月，安乐死后经常收集粪便和血液样本，并收集组织。基于INF-γELISA和组织培养，然后进行qPCR，使用最终大小（FS）模型和易感感染模型估算基本繁殖率（R0）。此外，使用一般线性化方法（GLM）模型和基于培养的粪便样本的培养物进行qPCR估计易感性感染易感性模型，使用通用线性方法（GLM）模型估算新脱落事件的传播速率参数（β）。由于敏感性的差异以及脱落事件持续时间的差异，分别为IN和CE犊牛得出R0。基于FS模型，血液样本中的干扰素-γ结果导致R 0 IG为0.90（0.24，2.59），组织培养导致R 0 T为1.36（0.45，3.94）。根据GLM模型，CE犊牛开始脱落的R0（R 0 CE）为3.24（1.14，7.41）。