Bovine tuberculosis (bTB) is prevalent in intensive dairy farms in Ethiopia. Vaccination could be an alternative control approach given the socio-economic challenges of a test-and-slaughter control strategy. The efficacy of the BCG was evaluated on 40 Holstein-Friesian (HF) and zebu crossbred calves recruited from single intradermal cervical comparative tuberculin (SICCT) test negative herds and randomly allocated into two groups. Twenty-two calves were vaccinated within two weeks of age, and 18 were kept as a control. Six weeks post-vaccination, the two groups were exposed and kept mixed with known SICCT test positive cows for one year. Immune responses were monitored by interferon gamma (IFN-) release assay (IGRA), SICCT test and antibody assay. Vaccinated calves developed strong responses to the SICCT test at the sixth week post-vaccination, but didn’t respond to ESAT-6/CFP-10 peptide antigens-based IGRA. During the exposure, IFN- response to the specific peptides cocktail (F(2.44, 92.67) = 26.96; p < 0.001) and skin reaction to the specific proteins cocktail (F(1.7, 64.3); p < 0.001) increased progressively in both groups while their antibody responses were low. The prevalence of bTB was 88.9% (95% CI: 65.3–98.6) and 63.6% (95% CI: 40.7–83.8) in the control and vaccinated calves, respectively, based on M. bovis isolation, giving a direct protective efficacy estimate of 28.4% (95% CI: -2.7–50.1). The proportion of lesion in vaccinated calves was 7.0% (34/484) against 11.4% (45/396) in control calves, resulting in a 38% (95% CI: 5.8–59.4) reduction of lesions. Besides, the severity of pathology was significantly lower (Mann Whitney U test, p < 0.05) in vaccinated (Median score = 2.0, IQR = 0 – 4.75) than in control (Median score = 5, IQR = 3.0 – 6.25) calves. Moreover, survival from M. bovis infection in vaccinated calves was significantly (Log-rank test: χ2= 7.796, p < 0.01) higher than that of the control calves. In conclusion, the efficacy of BCG was low, but the reduced frequency and severity of lesion in vaccinated calves could suggest its potential role in containing onward transmission.

中文翻译：

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评估卡介苗对埃塞俄比亚荷斯坦-弗里斯兰和瘤牛杂交小牛的牛结核病接触挑战的保护作用

牛结核病 (bTB) 在埃塞俄比亚的集约化奶牛场中很普遍。鉴于测试和屠宰控制策略的社会经济挑战，疫苗接种可能是一种替代控制方法。在 40 头荷斯坦 - 弗里斯兰 (HF) 和瘤牛杂交小牛上评估了 BCG 的功效，这些小牛从单个皮内宫颈比较结核菌素 (SICCT) 测试阴性牛群中招募并随机分配到两组。在两周龄内接种了 22 头小牛，并保留了 18 头作为对照。接种疫苗六周后，两组暴露并与已知的 SICCT 测试阳性奶牛混合一年。通过干扰素γ（IFN-）释放试验（IGRA）、SICCT试验和抗体试验监测免疫反应。接种疫苗的小牛在接种后第六周对 SICCT 测试产生强烈反应，但对基于 ESAT-6/CFP-10 肽抗原的 IGRA 没有反应。在暴露期间，IFN- 对特定肽混合物的反应 (F(2.44, 92.67) = 26.96; p < 0.001) 和皮肤对特定蛋白质混合物的反应 (F(1.7, 64.3); p < 0.001) 在两组，而他们的抗体反应都很低。基于牛分枝杆菌的分离，对照和接种疫苗的小牛中 bTB 的患病率分别为 88.9%（95% CI：65.3-98.6）和 63.6%（95% CI：40.7-83.8），给出了直接的保护效力估计28.4%（95% CI：-2.7–50.1）。接种疫苗的小牛的病变比例为 7.0% (34/484)，而对照小牛的病变比例为 11.4% (45/396)，导致病变减少 38% (95% CI: 5.8-59.4)。此外，病理的严重程度显着降低（Mann Whitney U 检验，p < 0。05) 接种疫苗的小牛（中位数分数 = 2.0，IQR = 0 – 4.75）比对照（中位数分数 = 5，IQR = 3.0 – 6.25）的小牛。此外，接种疫苗的小牛从牛分枝杆菌感染的存活率显着高于对照小牛的存活率（对数秩检验：χ2 = 7.796，p < 0.01）。总之，BCG 的功效较低，但接种疫苗的小牛病变频率和严重程度的降低可能表明其在遏制向前传播方面的潜在作用。