ABSTRACT
The presence of infectious bronchitis virus (IBV) was identified for the first time in the poultry population in Poland at the end of the 1960s. From this time a few waves of epidemics caused by different IBV variants spread across the country. In order to gain more insight into the molecular epidemiology of IBV in Poland, in the present study the S1 coding region of 34 IBV isolates and nearly whole genome of 10 strains collected over a period of 38 years was characterized. Phylogenetic analysis showed that these strains belonged to five recently established IBV lineages: GI-1, GI-12, GI-13, GI-19 and GI-23. Additionally, two strains from 1989 and 1997 formed a separate branch of the phylogenetic tree categorized as unique early Polish variants, and one strain was revealed to be the recombinant of these and GI-1 lineage viruses. Irrespective of year of isolation and S1-dependent genotype, the genome sequences of Polish IBV strains showed the presence of six genes and 13 ORFs: 5'UTR-1a-1b-S-3a-3b-E-M-4b-4c-5a-5b-N-6b-3'UTR, however their individual genes and putative proteins had different lengths. The phylogenetic analyses performed on the genome of ten Polish IBV strains revealed that they cluster into different groups. The Polish GI-1, GI-19 and GI-23 strains cluster with other similar viruses of these lineages, with the exception of the two strains from 1989 and 1997 which are different. It seems that in Poland in the 1980s and 1990s IBV strains with a unique genome backbone circulated in the field, which were then replaced by other strains belonging to other IBV lineages with a genome backbone specific to these lineages. The recombination analysis showed that some Polish strains resulted from a recombination event involving different IBV lineages, most frequently GI-13 and GI-19.