Crawford R P, Adams L G, Ficht T A, Templeton J W, Williams J D
Department of Veterinary Anatomy and Public Health, College of Veterinary Medicine, Texas A&M University, College Station 77843-4468.
Am J Vet Res. 1991 Nov;52(11):1848-51.
Seventy-nine cattle in all stages of gestation were inoculated with a low dose (2.5 x 10(8) colony-forming units) of Brucella abortus strain 19, then challenge exposed with pathogenic B abortus strain 2308 during the subsequent gestation. A brucellosis case was defined by isolation of strain 2308 from dam or calf samples. Cumulative incidence of brucellosis cases was 48, 33, 25, or 47% for cattle that were, respectively, not pregnant, or 19 to 87, 100 to 167, or 190 to 253 days in gestation at vaccination. The cumulative incidence was 56% in 27 nonvaccinated controls. The 95% confidence intervals for risk ratios included 1 in all cattle, except those that were 100 to 167 days in gestation at vaccination (ie, second trimester); the confidence interval for this group was 0.21 to 0.97. The prevented fraction (1-risk ratio) attributed to strain 19, in ascending order, was 0.14, 0.16, 0.4, or 0.55, respectively, for cattle that were not pregnant, or were 190 to 253, 19 to 87, or 100 to 167 days in gestation at vaccination. Potential confounders of breed, pen effect, and gestation days at challenge exposure did not significantly affect results. Results supported the hypothesis that stage of gestation at vaccination will affect the prevented fraction of brucellosis, or efficacy of strain 19, in cattle vaccinated with a low dose and, therefore, is one factor that may explain variation in strain 19-induced protection.
79头处于不同妊娠阶段的母牛接种了低剂量（2.5×10⁸菌落形成单位）的流产布鲁氏菌19菌株，随后在接下来的妊娠期用致病性流产布鲁氏菌2308菌株进行攻毒暴露。布鲁氏菌病病例定义为从母牛或犊牛样本中分离出2308菌株。对于接种时分别未怀孕、妊娠19至87天、100至167天或190至253天的母牛，布鲁氏菌病病例的累积发病率分别为48%、33%、25%或47%。27头未接种的对照牛的累积发病率为56%。除接种时妊娠100至167天（即妊娠中期）的母牛外，所有母牛风险比的95%置信区间均包含1；该组的置信区间为0.21至0.97。接种时未怀孕、妊娠190至253天、19至87天或100至167天的母牛，归因于19菌株的预防分数（1 - 风险比）分别为0.14、0.16、0.4或0.55。品种、畜栏效应和攻毒暴露时的妊娠天数等潜在混杂因素对结果无显著影响。结果支持了以下假设：接种时的妊娠阶段会影响低剂量接种母牛布鲁氏菌病的预防分数或19菌株的效力，因此是可能解释19菌株诱导的保护作用差异的一个因素。
