An Analysis of the Difference Between a Destructive and a Vaccine Strain of NDV (Newcastle Disease Virus) in the Chick Embryo

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Abstract
Summary: Three strains of NDV (CG179, B and vaccine), differing from each other in virulence for chickens and chicks, multiplied equally well in the allantoic sac of embryos and attained a maximum titer about 24 hours after allantoic inoculation. This was demonstrated both by repeated sampling of the same embryo and by titering pooled allantoic fluids from different eggs at different intervals. The results of the two methods were identical. The virulent strain (CG179) multiplied rapidly in all tissues of the embryo and produced an early viremia and a fulminating infection. The embryos died in less than 48 hours. In contrast, the vaccine strain gained entrance to the blood much later, and multiplied slowly in embryo tissues such as muscle, liver and brain. However the lungs of 16–17 day old embryos were particularly susceptible to this strain of virus. The severe pneumonia was accompanied by an accumulation of a large amount of virus in this tissue.