Rapid selection in chickens of subpopulations within ArkDPI-derived infectious bronchitis virus vaccines

Abstract

We examined spike (S) gene sequences of the virus populations of four different commercial ArkDPI-derived infectious bronchitis coronavirus vaccines before and during a single passage in specific pathogen free chickens. We found different degrees of genetic heterogeneity among the four vaccines before passage in chickens, ranging from no apparent heterogeneity to heterogeneity in 20 positions in the S gene. In all except one position, nucleotide differences were non-synonymous. The majority of amino acid differences were in the S1 subunit of the protein. For three of the four ArkDPI-derived vaccines, a single subpopulation with an S gene sequence distinct from the vaccine majority consensus at 5 to 11 codons was selected in chickens within 3 days after ocular vaccination. In contrast, we obtained no evidence for selection of specific subpopulations of the fourth ArkDPI-derived vaccine or Massachusetts or DE072 serotype vaccines. The virus subpopulations within each vaccine selected by chickens are similar in their S1 gene sequences, but distinct in the 3? portion of the S2 subunit gene for each of the three vaccines. In the S1 gene, the selected subpopulations are more similar to the virulent parental ArkDPI isolate than to the predominant vaccine population. The different proportions of distinct subpopulations in Ark vaccines apparently more fit for replication in the respiratory tract of chickens might cause different degrees of damage to respiratory epithelium and/or immune responses in vaccinated chickens. Sequence comparisons provided no evidence to support that ArkDPI-like field isolates were derived directly from host-selected vaccine virus subpopulations.

Altered pathogenicity, immunogenicity, tissue tropism and 3′-7kb region sequence of an avian infectious bronchitis coronavirus strain after serial passage in embryos

“…This substitution was maintained for P70 and P110, indicating that this residue was likely to be important for virus pathogenicity. However, other amino acid substitutions in the S1 protein were not observed between the M41 vaccine strain and M41 challenge strain [50], the 4/91 pathogenic and 4/91 attenuated strains [9,51], the TW1171/92 pathogenic and TW1171/92 attenuated strains, the TW2296/95 pathogenic and TW2296/95 attenuated strains, the TW2575/98 pathogenic or TW2575/98 attenuated strains [48], or the ArkDPI strain [52]. Investigations with other coronaviruses have shown that the S protein is a determinant of pathogenicity; however, the replacement of the S protein gene of the apathogenic Beaudette strain with that of the pathogenic M41 strain resulted in a recombinant virus that was still not pathogenic [53].…”

Combined infectious bronchitis virus Arkansas and Massachusetts serotype vaccination suppresses replication of Arkansas vaccine virus

“…Consequently following combined vaccination, the efficiently replicating Mass vaccine adds difficulty to the establishment of the Ark vaccine population. Furthermore, in the previous study reported by van Santen and Toro (2008) no selection of Mass vaccine virus subpopulations was observed; the S1 sequence of virus detected in vaccinated chickens was identical to that of the predominant S1 sequence found in vaccine vials. This may mean the vast majority of viruses contained in the Mass vaccine are able to efficiently replicate in the chicken, unlike Ark vaccine where only a minor component is able to efficiently replicate.…”

Avian coronavirus infectious bronchitis virus susceptibility to botanical oleoresins and essential oils in vitro and in vivo

“…Previously reported studies have shown that Arkansas type vaccine is the most prevalent virus in the commercial broilers and is capable of persisting in the flock (Jackwood et al, 2005;McKinley et al, 2008;Nix et al, 2000;van Santen and Toro, 2008). Vaccine virus was used in this experiment because colony houses (necessary to house the number of birds needed for the experiment) are not biologically secure, preventing us from using pathogenic isolates of IBV.…”