Research Notes: Evaluation of recombinant Newcastle disease virus expressing gB protein of infectious laryngotracheitis virus as bivalent in ovo vaccine.

Infectious laryngotracheitis (ILT) and Newcastle disease (ND) are 2 highly infectious avian respiratory diseases that have caused significant economic losses in the poultry industry worldwide. In ovo vaccination is administered during the late stage of incubation and is an attractive immunization method for poultry industry. However, most of the avian live vaccine strains that are safe for use after hatching are highly pathogenic to chicken embryos and therefore unsafe for in ovo vaccination. Previously, a recombinant Newcastle disease virus (NDV) strain, rTS-gB, expressing the gB protein of Infectious laryngotracheitis virus (ILTV), was demonstrated to be safe and immunogenic as a bivalent vaccine for hatched birds. In this study, we evaluated the safety and protective efficacy of rTS-gB as an in ovo vaccine. This vaccine strain was found to be safe for in ovo vaccination, with a hatchability and survival rate of 93.3% in chickens vaccinated in ovo with rTS-gB. In ovo vaccination with rTS-gB induced effective ILTV- and NDV-specific antibody responses in birds and conferred complete protection against virulent NDV and ILTV challenges. Furthermore, shedding of the challenged ILTV in cloacal and tracheal samples from in ovo vaccinated chickens was greatly reduced. These results indicate that the rNDV strain rTS-gB is a safe and highly immunogenic in ovo vaccine candidate against both ND and ILT.