Characteristics of lentogenic strains of Newcastle disease virus isolated in New Zealand.

Abstract Newcastle disease has not been recognised as a clinical entity in New Zealand, but several isolates of the causative virus have been obtained from domestic fowls, wild mallard ducks and an illegally imported parrot from Fiji. The viruses we obtained grew to high titre in fertile eggs, but embryonic death-rates were low, the patterns of death were-irregular and mean death-times were long. Transmission tests in day-old and older chickens caused no clinical disease. No drop in egg production was observed in laying birds. The-isolates were found to elute slowly from chicken erythrocytes, to show variable agglutinating activity with horse erythrocytes, and, especially those isolated from ducks, to be heat stable. They all failed to produce plaques in under 96 hours except in the presence of Mg SO4 or DEAE-dextran. It was concluded the isolates were of the lentogenic type and were virtually avirulent.