Efficacy and safety of an infectious bursal disease virus intermediate vaccine in ovo.

The study was divided into two experiments. In the first experiment, the efficacy of in ovo intermediate vaccine against infectious bursal disease virus (IBDV) was determined by challenge at 21 days of age with virulent IBDV in specific-pathogen-free (SPF) and commercial chickens. This vaccine was able to induce active immunity and to protect SPF chickens to challenge; protection was not complete in commercial chickens, as testified by bursal lesions, bursal index after challenge, and vaccine immunoresponse. In order to detect field and vaccinal viruses, immunoperoxidase staining, enzyme-linked immunosorbent assay, capture, and reverse transcriptase-polymerase chain reaction (RT-PCR) were tested; the RT-PCR was more effective at detecting both kind of viruses. In the second experiment, the immunosuppressive effect of in ovo vaccination was determined by evaluating the immunoresponse against Newcastle disease virus (NDV) vaccination effected at 10 days in both SPF and commercial chickens vaccinated in ovo. The in ovo vaccine causes a reduction of NDV immunoresponse, as testified by lowest geometric mean titer in group I (SPF chickens vaccinated against IBDV in ovo and against NDV at 11 days). In commercial chickens, immunoresponse to NDV vaccination was not influenced by in ovo vaccination.