Veterinary Epidemiology, Economics and Public Health, Department of Pathobiology and Population Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts, AL9 7TA, United Kingdom.
Veterinary Epidemiology, Economics and Public Health, Department of Pathobiology and Population Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts, AL9 7TA, United Kingdom.
J Dairy Sci. 2022 Oct;105(10):8354-8363. doi: 10.3168/jds.2021-21753. Epub 2022 Aug 31.
Johne's disease and bovine tuberculosis are diseases of economic, public health, and animal welfare importance. The single intradermal cervical comparative tuberculin (SICCT) test, which is used to determine bovine tuberculosis status as part of eradication schemes in the United Kingdom and some other countries, has been reported to interfere with the results of the widely used ELISA to detect antibodies against Mycobacterium avium ssp. paratuberculosis (MAP) in milk. Better understanding of the relationship between SICCT and MAP tests can improve management and control of Johne's disease. The aim of this study was to characterize the relationship between SICCT testing and milk ELISA performance and to assess whether the immunological response to the SICCT test is different for MAP-infected cows and noninfected cows. We used repeated MAP milk ELISA test results of a cohort of 805,561 cows in the United Kingdom between 2010 and 2018 that had milk ELISA tests within 90 d of SICCT testing to identify cows likely to be infected. We then assessed, separately, for cows deemed to be MAP-infected and noninfected, the association between MAP test results and proximity to SICCT testing by means of survival analysis and generalized additive mixed models. The results were used to quantify the effect SICCT testing may have on performance of milk ELISA tests conducted soon after SICCT testing. At high prevalence levels (20%) of MAP in the infected herd, overall accuracy of the milk ELISA is not reduced when testing occurs within 14 d from SICCT testing. Milk ELISA values of cows deemed to be infected were highest when MAP testing was closer in time to SICCT testing, suggesting the SICCT test enhances antibody response for MAP in infected cows. This corresponds to higher sensitivity of the MAP milk ELISA when testing within 30 d of the SICCT test. For cows deemed to be noninfected, the effect of previous SICCT testing was delayed compared with infected cows, with MAP milk ELISA values peaking at around 15 d post-SICCT testing. For both, MAP-infected and noninfected cows, interference from SICCT test diminished 30 d after SICCT testing, suggesting post 30 d to be the most appropriate time for evaluating the milk ELISA for MAP after SICCT testing. Our results provide strong evidence that the effect of the SICCT test on serological response against MAP is different for MAP-infected versus noninfected cows and that, as a result of this distinct effect, it is possible to improve interpretation of MAP milk ELISA test results (higher accuracy) by taking into consideration time since SICCT testing.
约氏病和牛结核病是具有经济、公共卫生和动物福利重要性的疾病。作为英国和其他一些国家根除计划的一部分，用于确定牛结核病状态的单一皮内颈比较结核菌素（SICCT）检测已被报道会干扰广泛使用的 ELISA 检测抗分枝杆菌 avium ssp. （MAP）抗体的检测结果。对 SICCT 检测和 MAP 检测之间关系的更好理解可以改善对约氏病的管理和控制。本研究的目的是描述 SICCT 检测与牛奶 ELISA 检测性能之间的关系，并评估对 SICCT 检测的免疫反应是否因感染 MAP 的奶牛和未感染的奶牛而不同。我们使用了英国 2010 年至 2018 年期间的 805561 头奶牛的重复 MAP 牛奶 ELISA 检测结果，这些奶牛在 SICCT 检测后 90 天内进行了牛奶 ELISA 检测，以确定可能感染的奶牛。然后，我们分别评估了被认为感染和未感染的奶牛，通过生存分析和广义加性混合模型来评估 MAP 检测结果与接近 SICCT 检测的关系。结果用于量化 SICCT 检测对 SICCT 检测后不久进行的牛奶 ELISA 检测性能的影响。在感染牛群中 MAP 的流行率水平较高（20%）时，当测试在距 SICCT 测试 14 天内进行时，牛奶 ELISA 的整体准确性不会降低。当 MAP 检测更接近 SICCT 检测时，被认为感染的奶牛的牛奶 ELISA 值最高，这表明 SICCT 检测增强了感染奶牛对 MAP 的抗体反应。这对应于在 SICCT 测试后 30 天内进行的 MAP 牛奶 ELISA 的更高灵敏度。对于被认为未感染的奶牛，与感染奶牛相比，以前的 SICCT 检测的影响延迟，MAP 牛奶 ELISA 值在 SICCT 检测后约 15 天达到峰值。对于两者，SICCT 检测的干扰在 SICCT 检测后 30 天减弱，这表明在 SICCT 检测后 30 天是评估 SICCT 检测后 MAP 牛奶 ELISA 的最合适时间。我们的结果提供了强有力的证据，表明 SICCT 检测对 MAP 血清学反应的影响因感染 MAP 的奶牛和未感染的奶牛而异，并且由于这种明显的影响，可以通过考虑自 SICCT 检测以来的时间来提高对 MAP 牛奶 ELISA 检测结果的解释（更高的准确性）。
