Field occurrence of avian infectious bronchitis virus in the Czech Republic and Slovakia

The epidemiological situation regarding the infectious bronchitis virus (IBV) population in Europe as well as the presence of predominant IBV strains is well described. The aim of this epidemiological study was to describe the real field situation in the Czech Republic and Slovakia, as no data are available for the last ten years. The study was also focused on differentiation between field IBV strains and vaccine/vaccine origin IBV strains in different poultry segments including backyard flocks. Between July 2013 and July 2016, cloacal, tracheal and/or visceral swab samples were collected from 145 Czech and Slovak chicken broiler, breeder and layer flocks. The majority of flocks was kept for production purposes, but to enable a more complete picture of the situation in the field backyard flocks with more than 50 birds were also included. As in other cases which were reported worldwide and based on collaboration with x-Ovo laboratories, samples were analysed using the real-time polymerase chain reaction (RT-qPCR) to detect the presence of the RNA of IBV. When positive, approximately 400 base pairs encoding the hypervariable region of the IBV S1 protein were sequenced. Sequencing results, cycle threshold values and vaccination history were used as criteria to try and distinguish vaccine strains from field strains. A significant percentage of all flocks presented clinical signs suggestive of IBV infection. From the total number of samples examined, 16.5% were negative. In 12.4% of the samples that did contain RNA from IBV, the genotype could not be determined. In most cases, this was due to the recovery of RNA quantities below the lower limit of detection of the sequencing PCR. The remaining positive samples predominantly contained RNA from IBV strains that belonged to the 4/91 - 793B - CR88 (44.7%), Massachusetts (30%), D274 - D207 (11.6%) and D388 - QX (8.7%) genotypes. Estimations indicated that approximately 23.9%, 48.4%, 58.3% and 0% of these detections, respectively, were vaccine strains. Infections with types UKR/27/2011, CK/CH/Guandong/Xindadi/0903 and K33/09 were observed sporadically. The results confirm that IBV infections are highly prevalent in Czech and Slovak chickens and that at least seven different IBV types were circulating during the monitored period. This underlines the necessity of providing flocks with a strong and broad protective immunity against IBV.