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

Abstract

Gallid alphaherpesvirus 1 causes infectious laryngotracheitis (ILT) in farmed poultry worldwide. Intertypic recombination between vaccine strains of this virus has generated novel and virulent isolates in field conditions. In this study, in vitro and in ovo systems were coinfected and superinfected under different conditions with two genomically distinct and commonly used ILTV vaccines. The progeny virus populations were examined for the frequency and pattern of recombination events using multi-locus high-resolution melting curve analysis of polymerase chain reaction products. A varied level of recombination (0 to 58.9%) was detected, depending on the infection system (in ovo or in vitro), viral load, the composition of the inoculum mixture, and the timing and order of infection. Full genome analysis of selected recombinants with different in vitro phenotypes identified alterations in coding and non-coding regions. The ability of ILTV vaccines to maintain their capacity to recombine under such varied conditions highlights the significance of recombination in the evolution of this virus and demonstrates the capacity of ILTV vaccines to play a role in the emergence of recombinant viruses.

Genetic Variation in the Glycoprotein B Sequence of Equid Herpesvirus 5 among Horses of Various Breeds at Polish National Studs

“…Despite these limitations, recombination was identified in 12 sequences. This was not surprising as recombination has been shown to contribute to the genomic variability observed among other herpesviruses [ 32 , 33 , 34 ]. However, the removal of putative recombinant sequences from the analyses did not reduce the level of variability observed between the remaining EHV-5 sequences, suggesting that mechanisms other than recombination must have contributed to the evolution of those sequences.…”

Analysis of Whole-Genome Sequences of Infectious laryngotracheitis Virus Isolates from Poultry Flocks in Canada: Evidence of Recombination

“…In the case of ILTV, the attenuated CEO vaccines are usually involved in recombination events with more frequency than the TCO vaccines, which could be influenced by the higher degree of attenuation of the TCO vaccine strains. Recombination between attenuated ILT vaccines (either CEO or TCO) depends on a number of factors including, but not limited to, the quantity and ratio of the vaccines used [ 17 ]. However, naturally occurring ILTV recombination events are common, and our results are in agreement with these studies [ 16 , 22 , 23 ].…”

“…Recombination can occur more frequently with the use of attenuated vaccines when coinfection with a vaccine and/or wild-type strain takes place. Furthermore, studies have provided evidence confirming recombination between ILTV strains [ 15 , 16 , 17 ], with recombination breaking points mostly identified within the UL and IR regions of the genome [ 18 , 19 ]. Recombination has been reported mostly among strains related to the CEO vaccines, resulting in new viruses with higher virulence than that of their parental strains [ 20 ].…”