Abstract：
Endemic infectious diseases remain a major challenge for dairy producers worldwide. For effective disease control programs, up-to-date prevalence estimates are of utmost importance. The objective of this study was to estimate the herd-level prevalence of bovine leukemia virus (BLV), Salmonella Dublin, and Neospora caninum in dairy herds in Alberta, Canada using a serial cross-sectional study design. Bulk tank milk samples from all Alberta dairy farms were collected 4 times, in December 2021 (n = 489), April 2022 (n = 487), July 2022 (n = 487), and October 2022 (n = 480), and tested for antibodies against BLV, S. Dublin, and N. caninum using ELISAs. Herd-level apparent prevalence was calculated as positive samples divided by total tested samples at each time point. A mixed effect modified Poisson regression model was employed to assess the association of prevalence with region, herd size, herd type, and type of milking system. Apparent prevalence of BLV was 89.4, 88.7, 86.9 and 86.9% in December, April, July, and October, respectively, whereas for S. Dublin apparent prevalence was 11.2, 6.6, 8.6, and 8.5%, and for N. caninum apparent prevalence was 18.2, 7.4, 7.8, and 15.0%. For BLV, S. Dublin and N. caninum, a total of 91.7, 15.6, and 28.1% of herds, respectively, were positive at least once, whereas 82.5, 3.6, and 3.0% of herds were ELISA-positive at all 4 times. Compared with the north region, central Alberta had a high prevalence (prevalence ratio (PR) = 1.13) of BLV-antibody positive herds, whereas south Alberta had a high prevalence (PR = 2.56) of herds positive for S. Dublin antibodies. Furthermore, central (PR = 0.52) and south regions (PR = 0.46) had low prevalence of N. caninum-positive herds compared with the north. Hutterite colony herds were more frequently BLV-positive (PR = 1.13) but less frequently N. caninum-positive (PR = 0.47). Large herds (>7,200 L/day milk delivered ∼ > 250 cows) were 1.1 times more often BLV-positive, whereas small herds (≤3,600 L/day milk delivered ∼ ≤ 125 cows) were 3.2 times more often N. caninum-positive. For S. Dublin, Hutterite-colony herds were less frequently (PR = 0.07) positive than non-colony herds only in medium and large stratum but not in small stratum. Moreover, larger herds were more frequently (PR = 2.20) S. Dublin-positive than smaller herds only in non-colony stratum but not in colony stratum. Moreover, N. caninum prevalence was 1.6 times higher on farms with conventional milking systems compared with farms with an automated milking system. These results provide up-to-date information of the prevalence of these infections that will inform investigations of within-herd prevalence of these infections and help in devising evidence-based disease control strategies.
摘要：
地方性传染病仍然是全球乳制品生产商面临的主要挑战。为了有效的疾病控制计划，最新的患病率估计至关重要.这项研究的目的是估计牛白血病病毒（BLV）的种群水平患病率，都柏林沙门氏菌,和新孢子虫在艾伯塔省的奶牛群中，加拿大采用连续横断面研究设计。收集了4次来自所有艾伯塔省奶牛场的散装罐奶样本，2021年12月（n=489），2022年4月（n=487），2022年7月（n=487），和2022年10月（n=480），并测试了针对BLV的抗体，都柏林，和N.caninum使用ELISA。群体水平表观患病率计算为阳性样品除以每个时间点的总测试样品。采用混合效应改进的泊松回归模型评估患病率与地区的相关性。牛群大小,牧群类型,和挤奶系统的类型。12月BLV的表观患病率为89.4、88.7、86.9和86.9％，April,七月,十月,分别,而都柏林的明显患病率为11.2%、6.6%、8.6%和8.5%，犬奈瑟菌的明显患病率分别为18.2%、7.4%、7.8%和15.0%。对于BLV，都柏林和加拿大北部，共有91.7、15.6和28.1%的牛群，分别,至少有一次是阳性的，而82.5、3.6和3.0％的牛群在所有4次均为ELISA阳性。与北部地区相比，阿尔伯塔省中部的BLV抗体阳性牛群的患病率很高（患病率比（PR）=1.13），而阿尔伯塔省南部的S.Dublin抗体阳性的牛群患病率很高(PR=2.56)。此外，与北部相比，中部（PR=0.52）和南部地区（PR=0.46）的犬根虫阳性牛群患病率较低。Hutterite菌落群的BLV阳性频率更高（PR=1.13），但犬N.caninum阳性频率较低（PR=0.47）。大群(>7200升/天牛奶交付~>250头奶牛)BLV阳性的频率是1.1倍，而小牛群(≤3,600升/天牛奶交付~≤125头母牛)是犬儒素阳性的3.2倍。对于都柏林来说，仅在中等和大地层中，Hutterite殖民地牛群的阳性频率（PR=0.07）比非殖民地牛群低，而在小地层中则没有。此外，较大的牛群更频繁（PR=2.20）。仅在非殖民地层中，而在殖民地层中，较小的牛群才是都柏林阳性。此外，与使用自动挤奶系统的农场相比，使用传统挤奶系统的农场的牛犬患病率高1.6倍。这些结果提供了这些感染患病率的最新信息，这些信息将为这些感染的群体内患病率调查提供信息，并有助于制定基于证据的疾病控制策略。
