Molecular characteristics of Budgerigar fledgling disease polyomavirus detected from parrots in South Korea.

BACKGROUND: Budgerigar fledgling disease polyomavirus (BFDV) is the pathogen that causes budgerigar fledgling disease in psittacine species. The clinical signs of PBFV infection include ascites, hepatitis, and crop stasis. BFDV is associated with a high mortality rate in nestling birds. In contrast, adult birds only have mild symptoms such as feather dystrophy. OBJECTIVES: This study aimed to determine the prevalence, genetic characteristics, and phylogenetic analysis of BFDV in pet parrots in Korea. METHODS: Fecal and tissue samples were collected from 217 pet parrots from 10 veterinary hospitals including Chungbuk National University Veterinary Hospital. The molecular screening was performed using polymerase chain reaction (PCR) analysis of the small t/large T antigen gene segment. Full-length genome sequencing with the Sanger and phylogenetic analysis were performed on BFDV-positive samples. RESULTS: The PCR results based on the small t/large T antigen gene marker indicated that BFDV DNA was present in 10 out of 217 screened samples. A whole-genome sequence was obtained from six strains and phylogenetic analysis revealed no significant relationship existed between the species and geographical locations amongst them. CONCLUSIONS: The prevalence of BFDV infection in South Korea is not high when compared to the prevalence of BFDV in other parts of the world, however, it has been reported sporadically in various species and geographic locations. The whole-genome analysis revealed 0.2%-0.3% variation in intragenomic homogeneity among the six strains analyzed. Korean strains are separately on the phylogenetic tree from their counterparts from China and Japan which might reflect the substantial genetic variation.

Genomic evolution of avian polyomaviruses with a focus on budgerigar fledgling disease virus.

Gammapolyomaviruses may cause serious inflammatory diseases in a broad range of avian hosts. In this study we investigated genomic evolution of and selection constraint acting on avian polyomaviruses (APyVs). Our analyses suggested that goose haemorrhagic polyomavirus (GHPV) evolves more slowly (3.03 × 10-5 s/s/y mean evolutionary rate) than budgerigar fledgling disease virus (BFDV), finch polyomavirus (FPyV) and canary polyomavirus (CaPyV) (1.39 × 10-4 s/s/y, 2.63 × 10-4 s/s/y and 1.41 × 10-4 s/s/y mean evolutionary rate, respectively). In general, purifying selection seems to act on the protein coding regions of APyV genomes, although positive Darwinian selection was also predicted in a few positions (e.g., in the large tumor antigen coding region of BFDV and GHPV and in the capsid protein sequences of BFDV). The importance of these aa changes remains elusive. Overall, a better understanding of adaptive changes in the genome of APyVs requires additional data from various incidental hosts and reservoir species.

Molecular Characterization of a Novel Budgerigar Fledgling Disease Virus Strain From Budgerigars in China.

Budgerigar fledgling disease virus (BFDV) is the causative polyomavirus of budgerigar fledgling disease, an important avian immunosuppressive disease in budgerigars (Melopsittacus undulatus). In the current study, we explored the etiological role and molecular characteristics of BFDV. We identified a novel BFDV strain, designated as SC-YB19, belonging to a unique cluster with three other domestic strains (WF-GM01, SD18, and APV-P) and closely related to Polish isolates based on complete sequences. Sequence analysis showed that SC-YB19 had an 18-nucleotide (nt) deletion in the enhancer region, corresponding to the sequence position 164-181 nt, which differed significantly from all other BFDV strains. Based on sequence alignment, three unique nucleotide substitutions were found in VP4 (position 821), VP1 (position 2,383), and T-antigen (position 3,517) of SC-YB19, compared with SD18, WF-GM01, QDJM01, HBYM02, APV7, and BFDV1. Phylogenetic analyses based on complete sequences suggested that SC-YB19, along with the domestic WF-GM01, SD18, and APV-P strains, formed a single branch and were closely related to Polish, Japanese, and American isolates. These results demonstrate that BFDV genotype variations are co-circulating in China, thus providing important insight into BFDV evolution.

Monitoring of free-ranging and captive Psittacula populations in Western Europe for avian bornaviruses, circoviruses and polyomaviruses.

Avian pathogens such as bornaviruses, circoviruses and polyomaviruses are widely distributed in captive collections of psittacine birds worldwide and can cause fatal diseases. In contrast, only little is known about their presence in free-ranging psittacines and their impact on these populations. Rose-ringed parakeets (Psittacula krameri) and Alexandrine parakeets (Psittacula eupatria) are non-native to Europe, but have established stable populations in parts of Western Europe. From 2012-2017, we surveyed free-ranging populations in Germany and France as well as captive Psittacula individuals from Germany and Spain for avian bornavirus, circovirus and polyomavirus infections. Samples from two out of 469 tested free-ranging birds (0.4%; 95% confidence interval [CI-95]: 0.1-1.5%) were positive for beak and feather disease virus (BeFDV), whereas avian bornaviruses and polyomaviruses were not detected in the free-ranging populations. In contrast, avian bornaviruses and polyomaviruses, but not circoviruses were detected in captive populations. Parrot bornavirus 4 (PaBV-4) infection was detected by RT-PCR in four out of 210 captive parakeets (1.9%; CI-95: 0.7-4.8%) from four different holdings in Germany and Spain and confirmed by detection of bornavirus-reactive antibodies in two of these birds. Three out of 160 tested birds (1.9%; CI-95: 0.5-5.4%) possessed serum antibodies directed against budgerigar fledgling disease virus (BuFDV). PaBV-4 and BuFDV were also detected in several psittacines of a mixed holding in Germany, which had been in contact with free-ranging parakeets. Our results demonstrate that Psittacula parakeets are susceptible to common psittacine pathogens and their populations in Western Europe are exposed to these viruses. Nevertheless, the prevalence of avian bornaviruses, circoviruses and polyomaviruses in those populations is very low.RESEARCH HIGHLIGHTS Psittacula parakeets are susceptible to bornavirus, circovirus and polyomavirus infection.Introduced Psittacula populations in Europe have been exposed to these viruses.Nevertheless, they may be absent or present at only low levels in free-ranging Psittacula populations.Free-ranging populations in Europe pose a minor threat of transmitting these viruses to captive Psittaciformes.