National Centre for Animal and Plant Health (CENSA), OIE Collaborating Centre for Disaster Risk Reduction in Animal Health, San José de las Lajas, Mayabeque, Cuba.
OIE Reference Laboratory for Classical Swine Fever, IRTA-CReSA, Campus de la Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.
BMC Vet Res. 2019 Jul 15;15(1):247. doi: 10.1186/s12917-019-1982-x.
Recent studies have hypothesized that circulation of classical swine fever virus (CSFV) variants when the immunity induced by the vaccine is not sterilizing might favour viral persistence. Likewise, in addition to congenital viral persistence, CSFV has also been proven to generate postnatal viral persistence. Under experimental conditions, postnatal persistently infected pigs were unable to elicit a specific immune response to a CSFV live attenuated vaccine via the mechanism known as superinfection exclusion (SIE). Here, we study whether subclinical forms of classical swine fever (CSF) may be present in a conventional farm in an endemic country and evaluate vaccine efficacy under these types of infections in field conditions.
Six litters born from CSF-vaccinated gilts were randomly chosen from a commercial Cuban farm at 33 days of age (weaning). At this time, the piglets were vaccinated with a lapinized live attenuated CSFV C-strain vaccine. Virological and immunological analyses were performed before and after vaccination. The piglets were clinically healthy at weaning; however, 82% were viraemic, and the rectal swabs in most of the remaining 18% were positive. Only five piglets from one litter showed a specific antibody response. The tonsils and rectal swabs of five sows were CSFV positive, and only one of the sows showed an antibody response. After vaccination, 98% of the piglets were unable to clear the virus and to seroconvert, and some of the piglets showed polyarthritis and wasting after 36 days post vaccination. The CSFV E2 glycoprotein sequences recovered from one pig per litter were the same. The amino acid positions 72(R), 20(L) and 195(N) of E2 were identified in silico as positions associated with adaptive advantage.
Circulation of chronic and persistent CSF infections was demonstrated in field conditions under a vaccination programme. Persistent infection was predominant. Here, we provide evidence that, in field conditions, subclinical infections are not detected by clinical diagnosis and, despite being infected with CSFV, the animals are vaccinated, rather than diagnosed and eliminated. These animals are refractory to vaccination, likely due to the SIE phenomenon. Improvement of vaccination strategies and diagnosis of subclinical forms of CSF is imperative for CSF eradication.
最近的研究假设，当疫苗诱导的免疫不是无菌时，经典猪瘟病毒（CSFV）变体的循环可能有利于病毒持续存在。同样，除了先天性病毒持续存在外，CSFV 也已被证明会产生产后病毒持续存在。在实验条件下，产后持续感染的猪无法通过称为超感染排斥（SIE）的机制对 CSFV 活减毒疫苗产生特异性免疫反应。在这里，我们研究在流行国家的常规农场中是否存在亚临床形式的经典猪瘟（CSF），并评估在这些类型的田间感染下疫苗的功效。
从 CSF 疫苗接种的母猪中随机选择了 6 窝仔猪，在 33 天龄（断奶）时来自古巴的一家商业农场。此时，仔猪接种了兔化活减毒 CSFV C 株疫苗。在接种前后进行了病毒学和免疫学分析。仔猪在断奶时临床健康；然而，82%的仔猪呈病毒血症，其余 18%的直肠拭子大部分呈阳性。只有一窝仔猪中的 5 只显示出特异性抗体反应。5 头母猪的扁桃体和直肠拭子均为 CSFV 阳性，只有 1 头母猪出现抗体反应。接种后，98%的仔猪无法清除病毒并产生血清转化，有些仔猪在接种后 36 天出现多发性关节炎和消瘦。从每窝仔猪中恢复的 CSFV E2 糖蛋白序列相同。E2 的 72(R)、20(L)和 195(N) 位氨基酸在计算机中被鉴定为与适应性优势相关的位置。
在疫苗接种计划下，在田间条件下证明了慢性和持续性 CSF 感染的循环。持续性感染占主导地位。在这里，我们提供的证据表明，在田间条件下，亚临床感染不会通过临床诊断检测到，并且尽管感染了 CSFV，但动物仍会接种疫苗，而不是进行诊断和消除。这些动物对疫苗接种有抵抗力，可能是由于 SIE 现象。改进疫苗接种策略和亚临床 CSF 的诊断对于 CSF 的根除至关重要。
