College of Veterinary Medicine, University of Zulia, Maracaibo, Venezuela.
J Clin Microbiol. 2012 Apr;50(4):1204-8. doi: 10.1128/JCM.06506-11. Epub 2012 Jan 11.
Here we report the biological and molecular characterization of a virulent genotype VII Newcastle disease virus (NDV) circulating in Venezuela and the assessment of the vaccination efficacy under field conditions compared to controlled rearing conditions. Biological pathotyping showed a mean embryo dead time of 50 h and an intracerebral pathogenicity index of 1.86. Sequence-based phylogenetic analysis demonstrated that the virus belongs to genotype VII in class II (a genotype often found in Asia and Africa), representing the first report of the presence of this genotype in the continent of South America. A vaccine-challenge trial in commercial broilers reared in fields or in a experimental setting included dual (live/killed) priming of 1-day-old chicks plus two live NDV and infectious bursal disease virus (IBDV) field vaccinations at days 7 and 17, followed by a very stringent genotype VII NDV challenge at day 28. Serology for NDV and IBDV, bursal integrity, and protection against NDV lethal challenge were assessed. At 28 days, field vaccinates showed significantly lower NDV (1,356 versus 2,384) and higher IBD (7,295 versus 1,489) enzyme-linked immunosorbent assay (ELISA) antibody titers than the experimentally reared birds. A lower bursal size and bursa-body weight ratio (P < 0.05) and higher bursa lesion score were also detected in the field set. Only 57.1% of field vaccinates survived the lethal challenge, differing (P < 0.05) from 90.5% survival in the experimental farm. Overall, results confirmed the presence of the genotype VII viruses in South America and suggest that field-associated factors such as immunosuppression compromise the efficacy of the vaccination protocols implemented.
在这里，我们报告了一种在委内瑞拉流行的毒力基因型 VII 新城疫病毒（NDV）的生物学和分子特征，并评估了与控制饲养条件相比，在野外条件下的疫苗接种效果。生物学病理定型显示，胚胎死亡时间的平均值为 50 小时，脑内致病性指数为 1.86。基于序列的系统发育分析表明，该病毒属于 II 类中的 VII 基因型（一种常见于亚洲和非洲的基因型），这代表了该基因型在南美洲大陆的首次报告。在商业肉鸡中进行的疫苗挑战试验，包括在野外或实验环境中对 1 日龄雏鸡进行双重（活/死）免疫接种，然后在第 7 天和第 17 天进行两次活 NDV 和传染性法氏囊病病毒（IBDV）田间接种，然后在第 28 天进行非常严格的 VII 基因型 NDV 挑战。对 NDV 和 IBDV 的血清学、法氏囊完整性以及对 NDV 致死性挑战的保护进行了评估。在第 28 天，野外接种疫苗的鸡的 NDV（1,356 比 2,384）和 IBD（7,295 比 1,489）酶联免疫吸附试验（ELISA）抗体滴度明显低于在实验农场饲养的鸡。在野外组中还检测到法氏囊体积较小和法氏囊-体重比（P < 0.05）以及法氏囊病变评分较高。只有 57.1%的野外接种疫苗的鸡在致死性挑战中存活，与实验农场的 90.5%存活率不同（P < 0.05）。总的来说，结果证实了 VII 基因型病毒在南美洲的存在，并表明与野外相关的因素，如免疫抑制，会影响实施的疫苗接种方案的效果。
