United States Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, Center for Epidemiology and Animal Health, 2150 Centre Avenue, Building B, Fort Collins, Colorado 80526, USA.
Current address: Colorado Division of Parks and Wildlife, Wildlife Health Program, 4330 Laporte Avenue, Fort Collins, Colorado 80521, USA.
J Wildl Dis. 2024 Apr 1;60(2):327-338. doi: 10.7589/JWD-D-21-00167.
Products of parturition are the predominant source of Brucella abortus for transmission in bison (Bison bison). Our objective was to assess whether preventing pregnancy in Brucella-seropositive bison reduced B. abortus shedding. Brucella-seropositive and -seronegative bison from Yellowstone National Park, Wyoming, USA were used in a replicated experiment. Each of two replicates (rep1, rep2) included a group of seropositive females treated with a single dose of gonadotropin-releasing hormone-based immunocontraceptive (Treatment rep1, n=15; Treatment rep2, n=20) and an untreated group (Control rep1, n=14; Control rep2, n=16) housed separately. Seronegative sentinel females were placed in each group to monitor horizontal transmission. Seronegative males were co-mingled for breeding each year. Pregnant females were removed from treatment groups in the first year, but not thereafter. Each January-June we monitored for B. abortus shedding events-any parturition associated with culture-positive fluids or tissues. We analyzed probability of shedding events using a negative binomial generalized linear mixed model fit by maximum likelihood using Laplace approximation. Over 5 yr, we observed zero shedding events in Treatment rep1 vs. 12 in Control rep1. All five Control rep1 sentinels but zero (0/5) Treatment rep1 sentinels seroconverted. In the second replicate, Treatment rep2 had two shedding events over 3 yr and Control rep2 had five events over 2 yr. Sentinels in both Control rep2 (3/6) and Treatment rep2 (5/6) seroconverted by trial endpoint. Treatment rep1 showed a reduced shedding probability relative to Control rep1, Treatment rep2, and Control rep2 (log odds value -25.36 vs. -1.71, -1.39, and -0.23, respectively). Fixed effect predictor covariates, year and age, had no explanatory value. These data suggest that successful contraception of brucellosis-seropositive female bison prevents shedding of B. abortus by individual animals. However, contraceptive treatment may or may not sufficiently reduce disease transmission to reduce brucellosis prevalence in an affected herd.
分娩产物是布氏杆菌流产亚种在野牛（美洲野牛）中传播的主要来源。我们的目标是评估在布鲁氏菌血清阳性野牛中预防妊娠是否会减少布氏杆菌流产亚种的脱落。我们使用了来自美国怀俄明州黄石国家公园的布鲁氏菌血清阳性和血清阴性野牛进行了重复实验。每个重复（rep1、rep2）包括一组用促性腺激素释放激素为基础的免疫避孕药（治疗组 rep1，n=15；治疗组 rep2，n=20）单次处理的血清阳性雌性动物和一个未处理的组（对照组 rep1，n=14；对照组 rep2，n=16）分别饲养。将血清阴性哨点雌性动物放置在每个组中以监测水平传播。每年血清阴性雄性动物都被混合用于繁殖。在第一年，从治疗组中取出怀孕的雌性动物，但此后不再取出。每年 1 月至 6 月，我们监测布氏杆菌流产亚种脱落事件——任何与培养阳性液体或组织相关的分娩。我们使用最大似然法通过拉普拉斯近似法拟合的负二项式广义线性混合模型分析脱落事件的概率。在 5 年期间，我们在治疗组 rep1 中观察到 0 次脱落事件，而在对照组 rep1 中观察到 12 次。对照组 rep1 中的所有 5 只哨点动物都发生了血清转化，但治疗组 rep1 中没有（0/5）。在第二个重复中，治疗组 rep2 在 3 年内有 2 次脱落事件，而对照组 rep2 在 2 年内有 5 次脱落事件。两个对照组 rep2（3/6）和治疗组 rep2（5/6）的哨点动物在试验结束时都发生了血清转化。与对照组 rep1、治疗组 rep2 和对照组 rep2 相比，治疗组 rep1 的脱落概率降低（对数优势值分别为-25.36、-1.71、-1.39 和-0.23）。固定效应预测协变量，年份和年龄，没有解释价值。这些数据表明，成功避孕布鲁氏菌血清阳性的雌性野牛可以防止个体动物脱落布氏杆菌流产亚种。然而，避孕治疗可能会或可能不会充分降低疾病传播率，从而降低受影响牛群中的布鲁氏菌病患病率。
