THE PATHOGENESIS OF INFECTION WITH A VIRULENT (CG 179) AND AN AVIRULENT (B) STRAIN OF NEWCASTLE DISEASE VIRUS IN THE CHICKEN

Abstract

Circulating antibody appeared in the convalescing NDV-infected chicken concomitantly with the disappearance of virus from the tissues. The antigenic response to the CG179 and B strains was demonstrated to be approx. equal. The neutralization test in the embryo and the hemagglutination inhibition technic yielded parallel results in the measurement of antibody early in convalescence, but late in convalescence the hemagglutination inhibition titers were relatively lower, indicating the possible duality of the antibodies. There was a wide ratio between the neutralizing antibody titers found in the brain and in the serum after an asymptomatic infection with NDV. The antibody level in the brain appeared to be related to the extent of virus growth and damage in the central nervous system. It appeared likely that a major factor in determining the virulence of the CG179 strain was the more rapid attainment in the CNS of high virus concn., which outstripped the defense mechanisms of the host.