Safety and Efficacy of a Turkey Herpesvirus Vector Laryngotracheitis Vaccine for Chickens

Abstract

Turkey herpesvirus vector laryngotracheitis vaccine (HVT/LT) expressing the glycoprotein B gene of laryngotracheitis virus (LTV) has been developed. In vitro growth kinetics of HVT/LT were similar to those of parental turkey herpesvirus (HVT), FC-126 strain. Genetic and phenotypic stabilities of HVT/LT after in vitro (in cell culture) or in vivo (in chickens) passage were confirmed by various assays, including Southern blot analysis, western blot analysis, and an indirect immunofluorescence assay. Safety of HVT/LT was assessed by an overdose study as well as by a backpassage study in specific-pathogen-free (SPF) chickens. The overdose study indicated that HVT/LT did not cause any adverse effects in chickens. The backpassage study confirmed that HVT/LT does not revert to virulence after five passages in chickens. The vaccine did not transmit laterally from vaccinated chickens to commingled nonvaccinated chickens. Efficacy of HVT/LT was evaluated in SPF layer chickens after vaccination by the subcutaneous route at 1 day of age. The majority of the vaccinated chickens (92%-100%) were protected against challenge with virulent LTV at 7 wk of age. Efficacy of HVT/LT was further evaluated in broiler chickens from a commercial source after in ovo vaccination to embryos at 18 days of incubation. After challenge with virulent LTV at 21 and 35 days of age, 67% and 87% of HVT/LT-vaccinated chickens did not develop LT clinical signs, respectively, while 100% (21 days of age) and 73% (35 days of age) of the challenge control chickens showed clinical signs of LT. These results suggest that HVT/LT is a safe and efficacious vaccine for control of laryngotracheitis (LT).

Development of Vaccines for Poultry Against H5 Avian Influenza Based on Turkey Herpesvirus Vector

“…A number of HVT vector vaccines have been constructed and evaluated for their characteristics and efficacy against avian pathogens [21][22][23][24][25][26]. There are three important elements in HVT vector vaccines that can impact efficacy of these vaccines in chicken: insertion sites, antigen genes, and promoters.…”

“…There are three important elements in HVT vector vaccines that can impact efficacy of these vaccines in chicken: insertion sites, antigen genes, and promoters. Several insertion sites including US2, US10, UL39 [21], and an intergenic region between UL45 and UL46 (UL45/46) [24][25][26] have been evaluated. Out of these potential insertion sites, we demonstrated that insertion of extraneous genes at the UL45/46 site did not alter their capacity to replicate [26].…”

“…Indeed, HVTvectored Newcastle disease vaccine has been shown to be efficacious for 72 weeks after inoculation into day-of-age chicks [19]. For aforementioned reasons and also because of its large genome that can be potentially used for insertion of heterologous genes [20], HVT has been evaluated as vectors expressing protective antigen gene(s) of various poultry pathogens including NDV, infectious bursal disease virus (IBDV), and infectious laryngotracheitis virus (ILTV) [21][22][23][24][25][26]. These HVT vector vaccines have shown to be very safe and induce effective humoral and cellular immunity that is long lasting.…”

Genomic recombination between infectious laryngotracheitis vaccine strains occurs under a broad range of infection conditions in vitro and in ovo

“…Live attenuated vaccines are effective in reducing mortality, clinical signs [2,3] and controlling the outbreaks of disease [4]. Several recombinant or virally vectored vaccines are also in use or development and include ILTVs with deletions of virulence-related open reading frames (ORFs) [5,6], and fowl-pox virus (FPV) [7] and turkey herpesvirus (HVT) [8,9] expressing specific ILTV glycoprotein genes.…”

Characterization of two recombinant HVT-IBD vaccines by VP2 insert detection and cell-mediated immunity after vaccination of specific pathogen-free chickens

“…Bivalent recombinant HVT (rHVT) vaccines have been successfully used to induce protection in chickens against several diseases: Newcastle disease (ND) (Reddy et al, 1996;Palya et al, 2012;Rauw et al, 2014), avian influenza (AI) (Rauw et al, 2012;Soejoedono et al, 2012), IBD (Darteil et al, 1995;Tsukamoto et al, 2002;Bublot et al, 2007;Le Gros et al, 2009;Perozo et al, 2009;Lemiere et al, 2011), and infectious laryngotracheitis (Esaki et al, 2013). These rHVT vaccines offer the advantage of inducing an immune response against Marek's disease as well as against a second disease by inserting a foreign gene in the vector that encodes a specific protein to stimulate a protective immune response.…”