Avian Influenza Adenovirus-Vectored in Ovo Vaccination: Combination with Marek's Disease Vaccine

Abstract

Protective immunity against avian influenza (AI) can be elicited in chickens in a single-dose regimen by in ovo vaccination with a replication competent adenovirus (RCA)-free human adenovirus serotype 5 (Ad)-vector encoding either the AI virus H5 (AdH5) or H7 hemagglutinins (HA). In ovo vaccination is likely one of the most efficient mass vaccination delivery routes in commercial chickens. From an applied perspective, it is relevant to clarify whether other vaccines routinely delivered by the same route would interfere with Ad-vector vaccination when applied simultaneously. Marek’s disease virus (MDV) vaccination is routinely performed in ovo in the U.S. poultry industry. The overall aim of this study was to evaluate the effects of combined in ovo vaccination with the experimental AdH5 recombinant vaccine and commercially available MDV vaccines. When the AdH5 vaccine was used in combination with MDV vaccines, chickens responding to the AdH5 vaccine had similar AI antibody levels compared to AdH5-only vaccinated birds. However, combined vaccinated groups showed reduced vaccine coverage to AI which suggests some level of interference. The combination of AdH5 with MDV Rispens/HVT affected the vaccine coverage to AI more severely. This result suggests that the replication rate of the more aggressive Rispens strain of serotype 1 may have interfered with the Ad-vectored vaccine. Increasing the Ad concentration produced similar AI antibody titers and AI vaccine coverage when applied alone or in combination with the HVT/SB1 vaccine. Adenovirus DNA was detected in hatched chickens 2 days after hatch but was undetectable on day 9 post hatch. MDV DNA was detected in feather follicles of all vaccinated birds at 12 days of age. Thus, Ad-vector vaccination does not interfere with the efficacy of MDV vaccination using any of the commonly used vaccine strains.