Isolation, pathogenicity and study of some biological properties of an strain of Newcastle disease virus

A Newcastle virus strain isolated from broilers flock, was evaluated for pathogenicity and other biological propierties. The tests made were intracerebral pathogenicity index (ICPI), intravenous pathogenecity index (IVPI), intracloacal pathogenicity (ICPI) index in chickens free of antibodies, the mean death time (MDT) in chicken embryos, thermoestability of hemaglutinatin activity (THA) and rate of elution were done. The results showed an ICPI of 1,9 and an IVPI of 2,2. For the ICPI, 100% of the chickens showed some mucous secretion in trachea and severe bleedina in cloaca, 75% had presented hemorragic proventriculus and 25% hemorragic and necrosis in the intestinal tract. MDT was 57,6 hours and the THA was 15 min. The strain showed an intermediate elution time. The pathogenicity tests agree with those described in velogenic viscerotropic strains responsible for the Doyle type of the disease. The biological properties were considered intrinsicals for each strain as well as independent of the virulence.