[Comparative study of strains of Newcastle disease virus in cell cultures of chick embryo fibroblast].

Comparative investigations were carried out with local velogenic strains (2 viscerotropic--Haskovo and Bregovo, and neurotropic--Rosa and Toutrakan) and 6 standard strains of the Newcastle disease virus, belonging to various pathogenic groups, in tissue cultures of chick embryo fibroblasts. The four local strains as well as the velogenic one (The. GB) and the mesogenic standard strains (Komarov, Roakin, and Hertfordshire) were reproduced in such cultures, producing a clear cytopathic effect without preliminary adaptation passages. The two strains studied parallel to the others, that were of velogenic pathogenic type (La Sota and Hitchner B1) did not produce cytopathogenic effect, and the cultural liquids did not poses agglutination activity with regard to chicken erythrocytes. The average infection titers in tissue cultures of chick embryo fibroblasts (TCID50) for the particular strains in an experiment varied in a wide range and proved higher with the velogenic (regardless of the fact that they belonged to the viscero- and neurotropic pathogenic type) that with the mesogenic strains. The TCID50/cm3 titer ratio of the strains with regard to their corresponding infection titers in chick embryos (EID50/cm3) also varied in a wide range, but invariably in favour of EID50. The latter was more strongly expressed for the mesogenic strain than for the velogenic pathotype strain of the Newcastle disease in experimental conditions.