Evaluation of an inactivated vaccine for nephropathogenic infectious bronchitis virus

Aim: To evaluate an inactivated vaccine for nephropathogenic infectious bronchitis in broiler with special reference to its ability for passing maternal antibodies to broiler chicks. Materials and Methods: An inactivated vaccine against nephropathogenic infectious bronchitis (NIB), prepared using an isolate obtained from natural outbreak of NIB was administered to broiler parents at the point of lay, leaving the control birds unvaccinated. Eggs laid below the desired weight (> 52 g) by vaccinated hens were utilized for yolk serology. Chicks obtained from hens of both group were subjected for serology and challenge with wild type of nephropathogenic IB isolates. Serology of the yolk and serum was carried out using haemagglutination (HI) test and ELISA. Results: Yolk serology revealed a geometric mean titre of 415.9 and 15188 ± 768 in HI test and ELISA respectively on 28 days post vaccination (dpv) as against 16.0 and 1881 ± 86 in yolk from unvaccinated hens. The HI test and ELISA indicated that the level of maternal antibody (MAb) in the chicks obtained from vaccinated hens was significantly (P < 0.01) higher on seven days of age than that of chicks from unvaccinated hens. However, the level of Mab of the chicks obtained from vaccinated hens decreased to below the level of protection at two weeks of age. Wild isolate and another isolate obtained from different geographical area were used for challenge dividing the chicks from vaccinated and unvaccinated hens equally. Mortality was observed in the challenged chicks from vaccinated (one in heterologus challenge) and unvaccinated (two) hens. Examination of kidney specimens collected from dead chicks revealed mottling and severe congestion grossly and inflammatory, degenerative and necrotic changes microscopically. Conclusion: The partial cross-protection against heterologous challenge and incomplete protection against homologous challenge with wild isolates were noticed. Keyowrds: infectious bronchitis virus, nephropathogenicity, protection, vaccine