Corbett Caroline S, De Buck Jeroen, Orsel Karin, Barkema Herman W
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada.
Vet Res. 2017 Apr 28;48(1):27. doi: 10.1186/s13567-017-0431-8.
Current Johne's disease control programs primarily focus on decreasing transmission of Mycobacterium avium subsp. paratuberculosis (MAP) from infectious adult cows to susceptible calves. However, potential transmission between calves is largely overlooked. The objective was to determine the extent of MAP infection in calves contact-exposed to infectious penmates. Thirty-two newborn Holstein-Friesian calves were grouped into 7 experimental groups of 4, consisting of 2 inoculated (IN) calves, and 2 contact-exposed (CE) calves, and 1 control pen with 4 non-exposed calves. Calves were group housed for 3 months, with fecal samples were collected 3 times per week, blood and environmental samples weekly, and tissue samples at the end of the trial. The IN calves exited the trial after 3 months of group housing, whereas CE calves were individually housed for an additional 3 months before euthanasia. Control calves were group-housed for the entire trial. All CE and IN calves had MAP-positive fecal samples during the period of group housing; however, fecal shedding had ceased at time of individual housing. All IN calves had MAP-positive tissue samples at necropsy, and 7 (50%) of the CE had positive tissue samples. None of the calves had a humoral immune response, whereas INF-γ responses were detected in all IN calves and 5 (36%) CE calves. In conclusion, new MAP infections occurred due to exposure of infectious penmates to contact calves. Therefore, calf-to-calf transmission is a potential route of uncontrolled transmission on cattle farms.
当前的副结核病控制计划主要侧重于减少成年感染牛分枝杆菌副结核亚种（MAP）向易感犊牛的传播。然而，犊牛之间的潜在传播在很大程度上被忽视了。目的是确定接触感染性同栏伙伴的犊牛中MAP感染的程度。32头新生荷斯坦-弗里生犊牛被分为7个实验组，每组4头，包括2头接种（IN）犊牛、2头接触暴露（CE）犊牛和1个有4头未暴露犊牛的对照栏。犊牛群体饲养3个月，每周收集3次粪便样本，每周收集血液和环境样本，试验结束时收集组织样本。IN犊牛在群体饲养3个月后退出试验，而CE犊牛在安乐死之前单独饲养3个月。对照犊牛在整个试验期间群体饲养。所有CE和IN犊牛在群体饲养期间粪便样本MAP均呈阳性；然而，在单独饲养时粪便排菌已停止。所有IN犊牛在尸检时组织样本MAP呈阳性，7头（50%）CE犊牛组织样本呈阳性。没有犊牛产生体液免疫反应，而在所有IN犊牛和5头（36%）CE犊牛中检测到INF-γ反应。总之，由于感染性同栏伙伴与接触犊牛接触，发生了新的MAP感染。因此，犊牛到犊牛的传播是奶牛场中未得到控制的潜在传播途径。
