Influence of Natural Exposure to Infectious Bursal Disease and Marek's Disease Viruses on Antibody Production in Young Chickens Immunized with Killed Newcastle Disease Virus

Abstract

The immunological response was compared between chickens 3 weeks of age immunized with killed Newcastle disease virus (NDV) and then exposed naturally to infectious bursal disease (IBD) and Marek's disease (MD) viruses and unexposed control chickens free from IBD and MD.
Agar gel-precipitating (AGP) antibody against IBD was detected in all the chickens 2 weeks after exposure, and the antibody against MD in 3 of 7 chickens 6 weeks and in 4 of 6 chickens 7 weeks after exposure. The control chickens were negative for IBD and MD antibodies over a 7-week experimental period. A difference in immunological response to NDV assayed by hemagglutination-inhibition (HI) and serum neutralization tests was found between the exposed and control chickens. The mean antibody titer was significantly lower in the former than in the latter. When challenged with virulent NDV, All the control chickens were protected, but only 2 of 7 exp bsed chickens survived and responded with higher HI titers 2 week after challenge.
These findings indicate that young chickens vaccinated with killed NDV and subsequently exposed to IBD and MD had depressed antibody production and protection against challenge with virulent NDV.