Chicken embryonal vaccination with avian infectious bronchitis virus.

A commercial infectious bronchitis virus (IBV) vaccine of the Massachusetts 41 strain was injected in embryonating chicken eggs on embryonation day (ED) 18. The IBV vaccine was pathogenic for embryos, and it was passaged in chicken kidney tissue culture to reduce the pathogenicity. At the 40th tissue culture passage (P40-IBV), the virus became apathogenic for the embryos. Maternal antibody-positive or -negative chicks hatching from eggs injected with P40-IBV developed antibody to IBV and were protected against challenge exposure at 4 weeks of age with virulent Massachusetts 41 IBV. Although P40-IBV protected chicks when administered on ED 18, this virus did not protect chicks well if given at hatch. When combined with the turkey herpesvirus (HVT), P40-IBV given on ED 18 did not interfere with the protection against challenge exposure with virulent Marek's disease virus, nor did the presence of HVT interfere with protection by P40-IBV. Thus, under laboratory conditions, IBV vaccine could be combined with HVT to form a bivalent embryonal vaccine.