Genetic mutations in live infectious bronchitis vaccine viruses following single or dual in vitro infection of tracheal organ cultures.

Despite regular co-vaccination of two different strains of live infectious bronchitis vaccine viruses, little is known about possible mutations in these viruses following vaccination. As an alternative to chicks, this study used an in vitro infection model to identify single-nucleotide polymorphisms (SNPs) within the part-S1 gene of two live infectious bronchitis virus vaccine strains (793B and Massachusetts) following single or dual inoculation onto tracheal organ cultures. Results indicate that viral titres reduced over the duration of the study; conversely, the amount of detected infectious bronchitis virus genome increased. Results demonstrate a greater number of non-synonymous SNPs in both vaccine strains when they are co-inoculated, compared with the single inoculations. The influence of the increased SNP and hydrophobic properties of the translated proteins on the vaccine viruses' virulence is unknown.