PASSIVE PROTECTION OF SPECIFIC PATHOGEN-FREE CHICKS AGAINST INFECTIOUS BURSAL DISEASE BY IN-OVO INJECTION OF SEMI-PURIFIED EGG-YOLK ANTIVIRAL IMMUNOGLOBULINS

In order to develop an experimental model for passive immunity in SPF chickens, active neutralizing immunoglobulins (Ig) directed against in fectious bursal disease virus (IBDV) were extracted from the yolk of e ggs laid by conventional layers immunized against IBDV. Concentrated I g extracts were inoculated via the intra-vitellin route into 7-day-old embryonated SPF hen eggs. Although detrimental to hatchability, Ig in oculation resulted in hatching two series of SPF chicks with passive i mmunity against IBDV. The neutralizing and ELISA antibody titres at 1 day-old (respectively 12.64 and 13.15 log(2); and 4915 and 4277), the kinetics of decay of the anti-IBDV antibodies and the protection affor ded by passive antibodies against highly virulent IBDV challenge prove d highly consistent with data previously reported on conventional chic ks. In-ovo inoculation of purified egg-yolk immunoglobulins may hence be a good experimental model for anti-IBDV maternally-transmitted immu nity. This experimental model might possibly be adapted to other patho gens or vaccines for which interference with maternally derived antibo dies is a matter of concern at 1 day-old.