EXPERIMENTAL VARIATION OF NEWCASTLE DISEASE VIRUS
ARMY FOREIGN SCIENCE AND TECHNOLOGY CENTER CHARLOTTESVILLE VA
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Adaptation of Newcastle disease virus to guinea pigs was accompanied by the appearance of genetically dissimilar virions, which were successfully isolated by the method of serial dilution. Attenuation of the virus was accompained by a reduction in its enzymatic activity adsorption, elution, hemolysis, while a direct relationship was established between virulents and enzymatic activity. Enzymatically active variants were precipitated with formalinized erythrocytes, and an avirulent TA2 variant, isolated from the supernatent, was shown to be less active enzymatically. It is suggested that enzymatic activity could be used to select weakly virulent variants from pathogenic strains of the virus.