Gerganov G
Vet Med Nauki. 1987;24(5):3-10.
A strain of the Newcastle disease virus, denoted GF, was isolated from birds vaccinated twice with a live vaccine. In some flocks of the farm this strain has caused oligosymptomatic disease, and in others the infection has run a latent course. It was shown that the GF strain possessed unusual biologic properties--an extremely high virulence in vitro combined with a total lack of pathogenicity in vivo. With regard to the tests mean death time with 10-day-old chick embryos (44.6 h) and plaque morphology (a heterogeneous plaque population of clear plaques, sizing 0.5 to 3.5 mm) it was referred to the velogenic group. With regard to the intracerebral pathogenic index (1.21) it belonged to the mesogenic group. In terms of the intravenous pathogenic index (0) it had to be classified with the lentogenic group of of strains of the Newcastle disease virus. All these properties of the strain were shown to be stable. Besides the difficulties with its differentiation the behaviours of this strain pose a number of problems with regard to its origin and the variability of the Newcastle disease virus in nature, which are subject to discussion.
从两次接种活疫苗的禽类中分离出一株新城疫病毒，命名为GF。在该养殖场的一些鸡群中，该毒株引发了轻症疾病，而在其他鸡群中，感染呈潜伏性病程。结果表明，GF毒株具有不同寻常的生物学特性——体外具有极高的毒力，而体内完全没有致病性。就对10日龄鸡胚的平均死亡时间（44.6小时）和蚀斑形态（大小为0.5至3.5毫米的透明蚀斑的异质蚀斑群体）的检测而言，它被归为速发型毒株组。就脑内致病指数（1.21）而言，它属于中等毒力毒株组。就静脉致病指数（0）而言，它必须被归类为新城疫病毒毒株的缓发型毒株组。该毒株的所有这些特性都被证明是稳定的。除了难以区分外，该毒株的行为在其起源以及新城疫病毒在自然界中的变异性方面还引发了一些问题，有待讨论。
