Protection of chickens from infectious laryngotracheitis with a recombinant fowlpox virus expressing glycoprotein B of infectious laryngotracheitis virus

Infectious laryngotracheitis (ILT) is an economically important disease of chickens caused by a type I gallid herpesvirus, infectious laryngotracheitis virus (ILTV). The vaccines currently available are modified live viruses, which are effective in preventing disease outbreaks. However, they have often been associated with a variety of adverse effects including spread of vaccine virus to non-vaccinates, inadequate attenuation, production of latently infected carriers, and increased virulence as a result of in vivo passage. In this study, a recombinant fowlpox virus expressing glycoprotein B (gB) of ILTV (rFPV-ILTVgB) was constructed. Protection of specific pathogen free (SPF) and commercial chickens from ILT with the rFPV-ILTVgB and commercial ILTV vaccine (Nobilis ILT) were compared after challenge with a lethal dose of virulent ILTV. Both the rFPV-ILTVgB- and the Nobilis ILT-vaccinated SPF chickens were completely protected from death, while 90% of the unvaccinated chickens died after challenge. The immunized commercial chickens were also 100% protected with rFPV-ILTVgB, compared with 85% protected with Nobilis ILT. The protective efficacy was also measured by the antibody response to ILTV gB, isolation of challenge virus and polymerase chain reaction amplification of the ILTV thymidine kinase gene after challenge. The results showed that rFPV-ILTVgB could be a potential safe vaccine to replace current modified live vaccines for preventing ILT.