Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada T2N4N1.
Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, MN 55455.
J Dairy Sci. 2024 Jan;107(1):516-529. doi: 10.3168/jds.2023-23407. Epub 2023 Sep 13.
Mycoplasma bovis outbreaks in cattle, including pathogen spread between age groups, are not well understood. Our objective was to estimate within-herd transmission across adult dairy cows, youngstock, and calves. Results from 3 tests (PCR, ELISA, and culture) per cow and 2 tests (PCR and ELISA) per youngstock and calf were used in an age-stratified susceptible-infected-removed/recovered (SIR) model to estimate within-herd transmission parameters, pathways, and potential effects of farm management practices. A cohort of adult cows, youngstock, and calves on 20 Dutch dairy farms with a clinical outbreak of M. bovis in adult cows were sampled, with collection of blood, conjunctival fluid, and milk from cows, and blood and conjunctival fluid from calves and youngstock, 5 times over a time span of 12 wk. Any individual with at least one positive laboratory test was considered M. bovis-positive. Transmission dynamics were modeled using an age-stratified SIR model featuring 3 age strata. Associations with farm management practices were explored using Fisher's exact tests and Poisson regression. Estimated transmission parameters were highly variable among herds and cattle age groups. Notably, transmission from cows to cows, youngstock, or to calves was associated with R-values ranging from 1.0 to 80 secondarily infected cows per herd, 1.2 to 38 secondarily infected youngstock per herd, and 0.1 to 91 secondarily infected calves per herd, respectively. In case of transmission from youngstock to youngstock, calves or to cows, R-values were 0.7 to 96 secondarily infected youngstock per herd, 1.1 to 76 secondarily infected calves per herd, and 0.1 to 107 secondarily infected cows per herd. For transmission from calves to calves, youngstock or to cows, R-values were 0.5 to 60 secondarily infected calves per herd, 1.1 to 41 secondarily infected youngstock per herd, and 0.1 to 47 secondarily infected cows per herd. Among on-farm transmission pathways, cow-to-youngstock, cow-to-calf, and cow-to-cow were identified as most significant contributors, with calf-to-calf and calf-to-youngstock also having noteworthy roles. Youngstock-to-youngstock was also implicated, albeit to a lesser extent. Whereas the primary focus was a clinical outbreak of M. bovis among adult dairy cows, it was evident that transmission extended to calves and youngstock, contributing to overall spread. Factors influencing transmission and specific transmission pathways were associated with internal biosecurity (separate caretakers for various age groups, number of people involved), external biosecurity (contractors, external employees), as well as indirect transmission routes (number of feed and water stations).
牛支原体在牛群中的暴发，包括不同年龄组之间的病原体传播，目前尚未得到很好的理解。我们的目的是估计成年奶牛、幼畜和小牛之间的群内传播。对 20 个荷兰奶牛场的成年奶牛、幼畜和小牛进行了临床暴发牛支原体的调查，对每头奶牛进行了 3 次（PCR、ELISA 和培养）检测，对每头幼畜和小牛进行了 2 次（PCR 和 ELISA）检测，使用年龄分层易感-感染-清除/恢复（SIR）模型来估计群内传播参数、途径和农场管理实践的潜在影响。一个队列的成年奶牛、幼畜和小牛在 20 个荷兰奶牛场接受了采样，从奶牛身上采集血液、结膜液和牛奶，从小牛和幼畜身上采集血液和结膜液，在 12 周的时间内采集了 5 次。任何至少有一次实验室检测呈阳性的个体都被认为是牛支原体阳性。使用具有 3 个年龄层的年龄分层 SIR 模型来模拟传播动态。使用 Fisher 精确检验和泊松回归探索与农场管理实践的关联。在不同的牛群和牛的年龄组之间，估计的传播参数变化很大。值得注意的是，牛与牛、幼畜或小牛之间的传播与每群 10-80 个继发感染牛、每群 1.2-38 个继发感染幼畜和每群 0.1-91 个继发感染小牛的 R 值有关。在幼畜与幼畜、小牛或牛之间传播的情况下，R 值为每群 76-96 个继发感染幼畜、每群 41-76 个继发感染小牛和每群 107-107 个继发感染牛。在小牛与小牛、幼畜或牛之间传播的情况下，R 值为每群 60-60 个继发感染小牛、每群 41-41 个继发感染幼畜和每群 47-47 个继发感染牛。在农场内的传播途径中，牛与幼畜、牛与小牛和牛与牛被确定为最重要的传播途径，小牛与幼畜和小牛与牛也具有显著作用。小牛与小牛之间的传播也被涉及，尽管程度较轻。虽然主要关注的是成年奶牛的牛支原体临床暴发，但显然传播已经扩展到了小牛和幼畜，这对整体传播有影响。影响传播的因素和特定的传播途径与内部生物安全（不同年龄组的单独护理人员、参与人数）、外部生物安全（承包商、外部员工）以及间接传播途径（饲料和水站数量）有关。
