Introduction
Recombination between different strains of the avian alphaherpesvirus infectious laryngotracheitis virus (ILTV) has been identified as a key process in ILTV evolution since it was first detected in 2012. This study aimed to characterise how prior vaccination of specific pathogen free (SPF) chickens might influence the virus populations after direct challenge with 2 ILTV strains. Viruses recovered from vaccinated birds were investigated by the characterisation of common recombination pattern and full genome sequencing of prominent recombinants.
Methods
Specific pathogen free (SPF) chickens in isolators were vaccinated using commercially available vaccines using three different vaccine strategies. They were then directly co-infected with two ILTV field strains. Tracheal swabs were collected from the birds at regular time intervals. Viruses recovered from tracheal swabs were plaque purified and subjected to a TaqMan single nucleotide polymorphism (SNP) genotyping assay that was used to detect recombination patterns in directly co-inoculated birds. In vitro characterisation including growth kinetics and cell mortalities, and whole genome sequencing were investigated for prominent recombinants.
Results
Vaccination via drinking water yielded a low level of clinical protection and resulted in a wide variety of recombinant progeny viruses. Recombinants were most prevalent on days 4 and 6 post inoculation. Common recombination patterns in directly co-inoculated birds were identified and these recombinants showed different growth kinetics when studied in vitro. Whole genome sequencing was performed for common recombinants.
Conclusions
Investigating the effects of vaccine strategies on ILTV recombination provides opportunities to understand recombination, its role in virulence and transmissibility, as well as to develop better vaccination strategies to help control disease. Further studies on prominent recombinants in vivo will help understand their pathophysiology and virulence.