Occurrence of bornaviruses, circoviruses and polyomaviruses in necropsy samples from parrots in Poland (2014-2024).

Introduction: Proventricular dilatation disease (PDD) is a disease of parrots which has been known for many years, but only in 2008 was it confirmed that its cause is avian bornavirus (ABV). Further disease aetiology and epidemiology information came subsequently. Later research distinguished an eight-genotype group of parrot bornaviruses (PaBV) infecting psittacines. In addition to PaBV, circoviruses (beak and feather disease viruses - BFDV) and avian polyomaviruses (APyV) also represent major viral pathogens of parrots. These may occur concurrently. This study's intent was to determine the occurrence of PaBV, BFDV and APyV in parrots in Poland between 2014 and 2024 and to compare it with extranational data. Material and Methods: Samples taken from 210 naturally deceased breeder-owned and pet parrots necropsied between 2014 and 2024 were studied. Tissue samples were analysed by RT-PCR (PaBV) and nested PCR (BFDV and APyV). Results: Parrot bornavirus RNA was detected in 50 parrots (23.8%), BFDV DNA in 59 (28%), and APyV DNA in 65 parrots (31%). A dilated proventriculus and gizzard - changes typical for PDD - were found in 22 (10.5%) cases and 18 were confirmed by a positive RT-PCR result. Thirty-two (15.2%) birds tested positive for PaBV despite the absence of obvious PDD lesions. Conclusion: Bornavirus infections in parrots in Poland occur relatively often, but less frequently than infections with polyomaviruses and circoviruses. Only 36% of the birds with confirmed bornavirus infections had changes typical for PDD observed in necropsy.