A recombinant turkey herpesvirus expressing chicken interleukin-2 increases the protection provided by in ovo vaccination with infectious bursal disease and infectious bronchitis virus

In ovo vaccination remains an attractive option for the mass application of vaccines to poultry, ensuring a uniform application of vaccine in a cost-effective manner. However, the number of vaccines that can be delivered safely by this method is limited. Several infectious bursal disease virus (IBDV) vaccines can be given in ovo though most are delivered post-hatch and there are no currently licensed embryo-safe infectious bronchitis virus (IBV) vaccines. Reduction in the dose of vaccines given in ovo is one possibility to ensure embryo safety though efficacy can be reduced when low doses are used. We have investigated the use of embryo-safe IBDV and IBV vaccines and the effects of co-delivery of a turkey herpesvirus recombinant expressing bioactive chicken IL-2 (IL-2/HVT). Co-delivery of the IL-2/HVT with low doses of the IBDV or IBV vaccines significantly increased the antibody response against these viruses. In addition the protection against challenge with virulent IBDV or IBV was increased significantly. This suggests that the co-delivery of IL-2/HVT with low doses of other vaccines in ovo may be one method to increase the number of vaccines that can be given safely and efficaciously via in ovo vaccination.