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.