Infectious bronchitis vaccine virus detection and part-S1 genetic variation following single or dual inoculation in broiler chicks

Abstract

An investigation was undertaken of the extent of genetic variation occurring within infectious bronchitis virus (IBV) vaccine strains following vaccination of day-old broiler chicks. Chicks were divided into seven groups, with two groups receiving single Massachusetts (Mass) vaccinations while the other four were inoculated with combinations of different IBV serotypes; Mass, 793B, D274 and Arkansas (Ark). The remaining group was maintained as an unvaccinated control. Following vaccination, swabs and tissues collected at intervals were pooled and RNA was extracted for detection of IBV by reverse transcription polymerase chain reaction. Positive amplicons were sequenced for the part-S1 gene and compared to the original vaccine strain sequences. Single nucleotide polymorphisms, amino acid variations and hydrophobicity changes were identified and recorded for each sampling point. A total of 106 single nucleotide polymorphisms were detected within 28 isolates. The average single nucleotide polymorphism counts of swab isolates were greater than those found in tissue samples. This translated into 64 amino acid changes; however only six resulted in a change to the hydrophobicity properties. All hydrophobic alterations occurred within swab isolates and the majority were recovered at 3 days post vaccination suggesting such changes to be detrimental to early virus survival. Nucleotide deletions were seen only in the group given the combination of Mass and Ark. Of the 16 sequenced samples in this group, 13 contained the same AAT deletion at position 1033 1035 in the Ark strains. Findings presented in this study demonstrate alteration in the S1 nucleotide sequence following co-administration of live IBV vaccines.

Comparative protective immunity provided by live vaccines of Newcastle disease virus or avian metapneumovirus when co-administered alongside classical and variant strains of infectious bronchitis virus in day-old broiler chicks

“…With both experiments, Sanger sequencing showed that the genotype of strains recovered using OP swabs altered from Mass to 793B after 14 dpv. As reported previously [26,27], while the Mass genotype made up the majority of detections during early sampling days (3-14 dpv), the 793B strain became the dominant strain by 21 dpv. The reason for the shifting of genotypes from Mass to 793B is not known, however, previous work has highlighted that different IBV strains can differentially induce host expression pathways, in particular TLR7 [65] and IFN-b [66].…”

“…IBV vaccinal strains have previously been shown to persist in chickens for a longer period [53,63]. To further investigate this, the growth kinetics and genetic characteristics of live IBV vaccines used in this study were cross compared with previous reports [26,64]. Vaccinal strains were detected in OP swabs throughout the current experiment, with the variant 793B strain dominating at the later ages of the birds.…”

“…At 7, 14, 21 dpv, five trachea and kidney samples were collected from each group. At 5 dpc, five trachea and kidney samples were collected and processed as previously described [26]. Blood was collected from ten chicks at 0 dpv and eight chicks at 21 dpv for the detection of IBV and NDV antibodies.…”

“…The d s /d ns ratio, to identify positive or purifying selection pressure for each group was calculated per day. This was done using the Nei-Gojobori method [45] where <1.0 indicated the recovered strains to be under positive selection pressure, and >1.0 indicated strains to be under purifying selection [26,46]. Positive or purifying selection was considered significant at P < 0.05.…”

“…Recent work has shown that IBV vaccines can undergo genetic mutations following inoculation into the chicken host [26,27]. As persistent mutations can alter strain characteristics [28], it is preferable to monitor potential changes.…”