Veterinary session

Chicken infectious bronchitis (IB) occurs world-wide and infects chickens and pheasants, predominantly causing respiratory diseases, though certain serotypes of IB viruses (IBV) may be nephropathogenic, cause falls in egg production and affect eggshell quality in laying hens.

The IBV genome has extensive genetic variability, which results in various pathogenicity and antigenic variations among the strains. This phenomenon presents challenges to vaccinal protection against the disease: the best protection can be achieved with homologous vaccine strains in relation to the challenge viruses, though broad protection range can be provided with the optimal combination of heterologous vaccine strains, even against diverse serotypes. Therefore, it has great importance to monitor the occurence of the prevailing serotypes/genotypes of IBVs on defined geographic areas.

The goal of this study was to survey Hungarian poultry flocks, both broiler and layer, either showing respiratory symptoms or not, for the presence of IBVs, and characterize the strains by nucleotide sequencing of a portion of the spike (S) glycoprotein gene of the genome. No similar study was conducted before in Hungary, therefore, it has great importance.

Organ samples including coecal tonsils, kidneys, and trachea were collected from broiler, layer, and breeder flocks, either from dead and culled birds and processed at the Scientific Support Laboratory of Ceva-Phylaxia, Budapest, by means of virus isolation, polymerase chain reaction (PCR), and nucleotide sequencing. Larger submissions, i.e. comprising of numerous samples were pre-screened by real-time quantitative PCR for the presence of the virus. The obtained sequences were submitted to phylogenetic analysis.

One third the 26 sampled flocks proved negative for IBV by the tests. Among the positives, one third belonged to the 4/91 serotype, a quarter to the QX serotype, and a single submission contained the D274 serotype.

The 4/91 and D274 hits presumably represent vaccine viruses based on the history of the concerned flocks. Interestingly, no Massachusetts type strain was detected in spite of the wide-scale application of vaccines containing this serotype.

The ratio of the QX positive samples coincides with widespread nature of this serotype in a few European countries, and its observed genetic variation among the sequenced strains confirms the established variability of the QX strains.