[Infectious bronchitis is ubiquitous - insights from 10 years of diagnostics in a poultry practice]

Infectious bronchitis (IB) is a highly contagious viral disease of chickens with global distribution and considerable economic impact. Due to the limited cross-protectivity between certain virus variants, vaccination programs routinely used today require regular evaluation and adaptation. The objective of this study was to describe the incidence and distribution of infectious bronchitis in western Germany and neighbouring regions based on a retrospective evaluation of diagnostic data obtained from flock health monitoring.

A total of 263 molecular diagnostic investigations for IB virus (221 from laying hens, 42 from broilers), conducted between 2015 and 2025, were evaluated retrospectively. Analyses were performed using real-time RT-PCR and supplemented by sequencing in selected samples. The classification of detected variants of infectious bronchitis virus (IBV) as vaccine or field strains was based on vaccination history in combination with sequencing results.

93.2% of samples tested positive for IBV (laying hens: 93.2%, broilers: 92.9%). The most frequently detected variants were QX and 793B. Multiple variants were detected simultaneously in 111 samples. The proportion of circulating variants remained largely consistent throughout the study period. In broilers, most detected IBV-variants (76.5%) were presumed to be vaccine strains, whereas in laying hens most variants (62.1%) were likely attributable to circulating field viruses. However, a definitive distinction between field and vaccine strains was only possible in a limited number of cases.

The results demonstrate the widespread presence of IB in poultry flocks. QX and 793B have consistently been the predominant variants in the study area (mainly North Rhine-Westphalia, but also adjacent regions) over recent years. However, the high number of simultaneous detections of multiple variants, as well as the frequent uncertainty in distinguishing between field and vaccine strains, emphasize the complexity of IB epidemiology. Therefore, diagnostic results should always be interpreted in conjunction with clinical and anamnestic data as well as additional diagnostic information.