Purification and Characters of the Newcastle Disease Virus (California Strain)

Abstract

A California strain of the virus of Newcastle disease of fowls, cultured in embryonated eggs, has been concentrated by ultracentrifugation of the virus-infected chorio-allantoic fluid. Electron micrographs of the concentrates revealed particles of a variety of sizes and shapes ranging from a graceful sperm-like form with headpiece and long, slender tail to stocky forms with relatively broad, short tails and to ovoid shapes without tails. With these particles there was associated the biological behavior of the virus,—hemagglutinative activity and infectivity. Sedimentation diagrams revealed two very diffuse boundaries with sedimentation rates of approximately S = 1800 and S = 1200. Physical criteria were not applicable to estimation of the purity of the concentrates, but it was judged, chiefly on the basis of the electron micrographs, that a large portion of the material represented virus. It is likely that the virus particle is essentially sperm-shaped, varying probably in the length and width of the head and possibly in the length of the tail. Chemically the virus is a complex of protein, about 67 per cent, lipid, about 27 per cent, and a relatively small amount of nucleic acid, some, at least, of which is of the desoxypentose type. The yield of virus varied from 10.9 to 6.4 mg per 100 ml of chorio-allantoic fluid. Hemagglutinative activity appeared to be proportional to virus content. The infectivity of the purified material was such that 10^−13.72 gm of virus constituted the 50-per-cent-point unit of infectivity for chick embryos.