Genomic recombination of infectious laryngotracheitis virus (ILTV) vaccines

Abstract

© 2020 Omid FakhriInfectious laryngotracheitis virus (ILTV) is an alphaherpesvirus that causes acute respiratory disease in chickens. This disease causes economic loss in poultry industries worldwide and is a major concern for animal health and welfare. Although, ILTV vaccines are in use to control disease, biosecurity breaches and continuous evolution of the ILTV genome make outbreak prevention difficult. Genomic recombination plays a role in diversification of herpesvirus genomes and has been suggested to be an important alternative evolutionary mechanism in herpesviruses such as ILTV. In previous studies of ILTV, two new genotypes of virulent field strains were shown to be independent recombinants derived from distinct attenuated commercial ILTV vaccines. These new strains became the dominant field viruses responsible for widespread and severe disease outbreaks in Australian poultry flocks. This project aimed to determine the frequency of these recombination events and the conditions that can facilitate recombination using in vitro, in ovo and in vivo studies. In these series of studies, a high-throughput and cost-effective method for detection of recombinant ILTVs was developed and was used to analyse the viruses generated under multiple infection conditions. The results from these analyses indicated that genomic recombination between vaccine strains of ILTV is a frequent event and takes place under a broad range of conditions. De novo mutation was detected in addition to genomic recombination. The capacity of ILTV vaccines to allow secondary infection by another ILTV vaccine (i.e. superinfection) was investigated at both cellular and natural host levels. The result of this investigation showed that superinfection can occur after administration of ILTV vaccines, providing the virus with ample opportunity for genomic recombination. The outcomes of these studies include advances in fundamental understanding about the factors that lead to ILTV recombination