Immunization of day-old chicks having maternally derived antibodies against infectious bronchitis: degree of protection as monitored by ciliary activity after intratracheal challenge.

One-day-old chicks with maternally derived antibodies were vaccinated against infectious bronchitis (IB) with 3000 EID50 of the IB vaccine virus designated H120. The degree of protection induced by intranasal-eye drop (IE) vaccination was compared to that achieved by spray (S) vaccination. The protection afforded by vaccination was monitored by intratracheal challenge with IBV strain M-41 (clinical signs, ciliary activity in tracheal explants, virus isolation) and by serological tests (ovoneutralization, microneutralization in cell culture, haemagglutination inhibition (HI) test, ELISA). Intranasal-eye drop vaccination provided protection against intratracheal challenge. Immunity developed around 31 days of age. Spray vaccination failed to give protection against challenge by the same route. No difference was demonstrable in effectiveness between the two routes of vaccination by serological tests. No elevation of the antibody level occurred in either group. The level of maternally derived antibodies declined with age.

Cross-protection studies with vaccine strain H-120 of infectious bronchitis virus using ciliary activity.

Forty 3-day-old chickens were immunized intratracheally and another 40 intranasally-intraocularly with vaccine strain H-120 of infectious bronchitis virus (IBV). The chickens were divided into groups of five and each group was challenged intratracheally or intranasally-intraocularly with one of 8 different heterologous strains of IBV 4 weeks after vaccination. The vaccinated chickens were protected against challenge with three heterologous strains (Massachusetts M41, B and AEG), showing 89, 86 and 89% ciliary activity, respectively, but were not protected against challenge with strains D-3896 and D-3128. Clinical signs and/or a reduction in ciliary activity was observed neither for the vaccinated nor for the unvaccinated groups challenged with strains Sz, D-207 and D-212. This suggests that these isolates have no primary pathogenic role in broiler flocks. The remaining 5 strains (M41, B, AEG, D-3896 and D-3128) caused mild respiratory signs and ciliostasis in birds of the unvaccinated groups.

Isolation and characterization of new infectious bronchitis virus variants in Hungary.

Two agents not agglutinating chicken erythrocytes were isolated, one in each of two flocks, from organ samples and tracheal swabs taken from 4- to 7-week-old chicks of 8 broiler flocks experiencing respiratory signs. Virus isolation was done in embryonated SPF hen's eggs. Morphological changes of the embryos, appearing as dwarfing or curling into a spherical form, usually occurred in the 3rd or 4th passage on postinoculation (PI) days 5-9. Some embryos had swollen kidneys covered with urate. Electron microscopy of ultrathin sections of these kidneys revealed the presence of virions reminiscent of coronaviruses. Similar viral particles were seen in resuspended pellets of isolates concentrated by ultracentrifugation. Based on embryo changes, cross-neutralization tests with type-specific antisera, physicochemical tests, results obtained in cell cultures, and electron microscopic findings the two isolates were identified as infectious bronchitis virus (IBV). By cross-neutralization tests the isolates differed from IBV reference strains M41 and H52 and can be considered distinct variants. Elucidation of their epizootiological role requires further investigations.