Protection Against Infectious Laryngotracheitis by In Ovo Vaccination with Commercially Available Viral Vector Recombinant Vaccines

Abstract

Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease of chickens caused by infectious laryngotracheitis virus (ILTV). The disease is mainly controlled through biosecurity and by vaccination with live-attenuated vaccines. The chicken embryo origin (CEO) vaccines, although proven to be effective in experimental settings, have limited efficacy in controlling the disease in dense broiler production sites due to unrestricted use and poor mass vaccination coverage. These factors allowed CEO vaccines to regain virulence, causing long lasting and, consequently, severe outbreaks of the disease. A new generation of viral vector fowl poxvirus (FPV) and herpesvirus of turkey (HVT) vaccines carrying ILTV genes has been developed and such vaccines are commercially available. These vaccines are characterized by their lack of transmission, lack of ILTV-associated latent infections, and no reversion to virulence. HVT-vectored ILTV recombinant vaccines were originally approved for subcutaneous HVT or transcutaneous (pox) delivery. The increased incidence of ILTV outbreaks in broiler production sites encouraged the broiler industry to deliver the FPV-LT and HVT-LT recombinant vaccines in ovo. The objective of this study was to evaluate the protection induced by ILTV viral vector recombinant vaccines after in ovo application in 18-day-old commercial broiler embryos. The protection induced by recombinant ILTV vaccines was assessed by their ability to prevent clinical signs and mortality; to reduce challenge virus replication in the trachea; to prevent an increase in body temperature; and to prevent a decrease in body weight gain after challenge. In this study, both recombinant-vectored ILTV vaccines provided partial protection, thereby mitigating the disease, but did not reduce challenge virus loads in the trachea.

Replication of recombinant herpesvirus of turkey expressing genes of infectious laryngotracheitis virus in specific pathogen free and broiler chickens followingin ovoand subcutaneous vaccination

“…Recently, two recombinant, virus-vectored vaccines (r-LT vaccines) for immunization of chickens against LT have been produced and are licensed for use in the USA (rHVT-LT and rFPV-LT) (Tong et al, 2001;Davison et al, 2006;Johnson et al, 2010). The rHVT-LT vaccine currently is licensed for in ovo administration; the rFPV-LT vaccine currently is licensed only for wingweb inoculation of breeder/layer chickens.…”

Newcastle Disease Virus (NDV) Recombinants Expressing Infectious Laryngotracheitis Virus (ILTV) Glycoproteins gB and gD Protect Chickens against ILTV and NDV Challenges

“…Other vectored vaccines for ILTV, including fowlpox viruses expressing glycoprotein B and HVT expressing glycoprotein I and D, are commercially available. These viral vector vaccines expressing ILTV glycoproteins have proven to be safe, and in particular the HVT vectored construct can significantly reduce the clinical disease; however, they are not as effective as live attenuated vaccines in reducing the shedding of challenge virus (12)(13)(14)(15)(16)47).…”

“…Viral DNA extraction from tracheal and ocular swab samples was performed using the MagaZorbH DNA Miniprep 96-well kit (Promega, Madison, WI) as described previously (12). Construction of a recombinant LaSota cDNA clone containing the GFP gene.…”

“…To overcome these problems associated with live attenuated ILTV vaccine strains, inactivated whole-virus vaccines and turkey herpesvirus (HVT) and fowlpox virus (FPV) vectors encoding ILTV antigens have been developed (10)(11)(12)(13)(14)(15). Although in protection studies these vaccines are completely safe when administered at different ages, they induce only partial protection compared with that induced by live attenuated vaccines (16).…”

The complexity of infectious laryngotracheitis virus: a focus on vaccination and challenge viruses

“…This may be why TCO vaccines have a reduced risk of reversion to virulence. In ovo vaccination provides protection at a very young age, unlike the traditional live attenuated vaccines, where vaccination may not occur until 6 weeks of age(14,26).The recombinant vaccines depend on the immunogenicity of herpesvirus glycoproteins. The main glycoproteins used in research are glycoproteins B, C, D G and I(2, 15,(27)(28)(29)(30)(31)(32).…”