Avian infectious bronchitis: specific lachrymal IgA level and resistance against challenge

Since circulating antibody titres against infectious bronchitis virus (IBV) often correlate poorly with protection against re-infection, the lachrymal specific IgA level of IBV vaccinated chickens was evaluated as an indicator of resistance against challenge. For this purpose, the post-vaccination (pv) IBV specific lachrymal IgA response was monitored in 30 chickens at 3-day intervals until a rise of this specific isotype was detected. On day 19 pv, all birds (vaccinated group and non-vaccinated controls) were challenged with the moderately attenuated H-52 IBV strain via the ocular route. Protection was assessed by viral reisolation attempts in SPF embryonated chicken eggs (ECE) from tracheal swabs 4 days after challenge. Virus was detected in all control birds by the second passage in ECE. IBV was reisolated from 27% (eight birds) of all H-120-primed birds after five passages in ECE. These results demonstrate that lachrymal-fluid-specific IgA levels in chickens are associated with resistance against IBV reinfection and are therefore a suitable source of antibodies that could be used for flock profiling.