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,
nephro-pathogenicity, protection, vaccine
