Asfaw Mersha, Senbit Menur, Yesuf Mohammed, Dagnaw Melkie, Birhan Girma, Abat Anmaw Shite, Ibrahim Saddam Mohammed
Department of Veterinary Pathobiology, College of Veterinary Medicine and Animal Sciences, University of Gondar, Gondar, Ethiopia.
Department of Veterinary Epidemiology and Public Health, College of Veterinary Medicine and Animal Sciences, University of Gondar, Gondar, Ethiopia.
Infect Drug Resist. 2022 Jun 8;15:2937-2948. doi: 10.2147/IDR.S365745. eCollection 2022.
In this study we aimed to provide preliminary evidence on the safety and efficacy of the currently used ovine pasteurellosis vaccine in Ethiopia using clinical and pathological endpoints.
Twenty, conventionally reared, apparently healthy, seronegative male lambs, were randomly classified into two groups of 10 animals as "vaccinated-challenged" and "unvaccinated-challenged controls". The first group received 1 mL of the licensed biotype A based vaccine subcutaneously while the second group received phosphate-buffered saline as a placebo. Following vaccination, lambs were monitored for one month for potential vaccine adverse reactions. Five weeks postvaccination, all lambs were immunosuppressed using dexamethasone, and intratracheally challenged with 5.2×10 CFU/mL live A1 (clinical isolates). Then, all lambs were followed up for eight days for clinical examination and necropsied on the ninth day postchallenge for pathological investigation.
There were no safety issues recorded during the study. In terms of clinical signs, lambs developed fever, depression, mucoid bilateral oculonasal discharge, coughing and sneezing regardless of their vaccination status. Fisher's exact test between vaccination status and each clinical sign showed a statistically insignificant association (>0.05). The main pathological findings in both groups were pulmonary congestion, atelectasis, emphysema, and suppurative bronchopneumonia. Consolidation lung lesion score of +1 (5/10 of vaccinated, 6/10 of unvaccinated) and +2 (3/10 of vaccinated, 4/10 of unvaccinated) were recorded in a statistically indifferent manner among both vaccinated and nonvaccinated groups (>0.05).
Collectively, the results suggested that the vaccine posed no safety concern and presumably lacks protective efficacy against local isolates. However, the study did not analyze antibody titer and their functionality using serum bactericidal assays. Further confirmatory studies could provide more evidence on the vaccine efficacy. Safety should further be assessed in a field setting involving a large number of animals to enable detection of rare vaccine adverse events.
在本研究中，我们旨在利用临床和病理终点，为埃塞俄比亚目前使用的绵羊巴氏杆菌病疫苗的安全性和有效性提供初步证据。
将20只常规饲养、外表健康、血清学阴性的雄性羔羊随机分为两组，每组10只，分别作为“接种疫苗-攻毒组”和“未接种疫苗-攻毒对照组”。第一组皮下注射1毫升许可的基于生物型A的疫苗，而第二组接受磷酸盐缓冲盐水作为安慰剂。接种疫苗后，对羔羊进行为期一个月的监测，以观察潜在的疫苗不良反应。接种疫苗五周后，所有羔羊使用地塞米松进行免疫抑制，然后经气管内接种5.2×10 CFU/mL的活A1（临床分离株）。然后，对所有羔羊进行为期八天的临床检查随访，并在攻毒后第九天进行剖检以进行病理调查。
研究期间未记录到安全问题。就临床症状而言，无论接种疫苗状况如何，羔羊均出现发热、抑郁、双侧眼鼻黏液性分泌物、咳嗽和打喷嚏。接种疫苗状况与每种临床症状之间的Fisher精确检验显示，两者之间的关联无统计学意义（>0.05）。两组的主要病理发现均为肺充血、肺不张、肺气肿和化脓性支气管肺炎。接种疫苗组和未接种疫苗组的肺实变病变评分为+1（接种疫苗组10只中有5只，未接种疫苗组10只中有6只）和+2（接种疫苗组10只中有3只，未接种疫苗组10只中有4只），两组之间无统计学差异（>0.05）。
总体而言，结果表明该疫苗不存在安全问题，可能对当地分离株缺乏保护效力。然而，该研究未使用血清杀菌试验分析抗体滴度及其功能。进一步的验证性研究可以为疫苗效力提供更多证据。应在涉及大量动物的现场环境中进一步评估安全性，以便能够检测罕见的疫苗不良反应。
