Successive efficacy evaluation of various commercial live-attenuated avian coronavirus vaccination schedules against challenge with circulating field strain of genotype 23 lineage

Background

Infectious bronchitis virus (IBV) is a highly spreading, evolving virus that induces multiple manifestations, including respiratory, urinary, and reproductive symptoms, posing a significant threat to the local poultry industry. This study evaluated a variety of IBV vaccination regimens in broilers using commercially available live attenuated vaccines such as IB Primer, 793/B (4/91), IB-VAR2, and H120 against the local novel IBV-GI-23.3 strain.

Methods

The vaccines were administered to eight groups of SPF chicks either at 1 day age or at 1+14 days of age. The birds were then challenged with the NewValley-1-EGYIBV-GI23.3-2023 strain via the oculo-nasal route at 28 days post-vaccination, using 106 EID50/0.2 ml/chick. Ciliostasis activity and the scores for histopathological lesions were evaluated at 7days post-challenge (DPC). Virus shedding was monitored at 3, 5, and 7 DPC using the real-time RT-PCR method.

Results

The ciliostasis test indicated that the vaccinated groups receiving the IB Primer + 4/91 vaccine regime at 1 day age or at 1+14 days of age provided the highest levels of protection (65%, 68%). Similarly, administrating of IB Primer-VAR2 at 1+14 days of age demonstrated substantial protection (63%). Conversely, administering the H120+4/91 vaccination protocol at days 1 and 14 resulted in a moderate level of protection (53%). Tracheal IBV shedding quantification and subsequent assessment of trachea, proventriculus, bursa, and kidney degenerative changes were significantly lower in the vaccinated groups than in the control groups.

Conclusion

The heterologous combined IB Primer +4/91 program demonstrated the most significant protective efficacy against the IBV field challenge strains in broiler chickens compared to other vaccines.