Genetic diversity of beak and feather disease virus detected in psittacine species in Australia

Prevalence, genotypes, and infection risk factors of psittacine beak and feather disease virus and budgerigar fledgling disease virus in captive birds in Hong Kong

Psittacine beak and feather disease virus (PBFDV) and budgerigar fledgling disease virus (BFDV) are significant avian pathogens that threaten both captive and wild birds, particularly parrots, which are common hosts. This study involved sampling and testing of 516 captive birds from households, pet shops, and an animal clinic in Hong Kong for PBFDV and BFDV. The results showed that PBFDV and BFDV were present in 7.17% and 0.58% of the samples, respectively. These rates were lower than those reported in most parts of Asia. Notably, the infection rates of PBFDV in pet shops were significantly higher compared to other sources, while no BFDV-positive samples were found in pet shops. Most of the positive samples came from parrots, but PBFDV was also detected in two non-parrot species, including Swinhoe's white-eyes (Zosterops simplex), which had not been reported previously. The ability of PBFDV to infect both psittacine and passerine birds is concerning, especially in densely populated urban areas such as Hong Kong, where captive flocks come into close contact with wildlife. Phylogenetic analysis of the Cap and Rep genes of PBFDV revealed that the strains found in Hong Kong were closely related to those in Europe and other parts of Asia, including mainland China, Thailand, Taiwan, and Saudi Arabia. These findings indicate the presence of both viruses among captive birds in Hong Kong. We recommend implementing regular surveillance for both viruses and adopting measures to prevent contact between captive and wild birds, thereby reducing the transmission of introduced diseases to native species.

Molecular detection and analysis of beak and feather disease viruses in Iran

The beak and feather disease virus (BFDV) is one of the few pathogens capable of causing extinction of psittacines. To determine the prevalence and the nature of BFDV mutation, this study investigated the presence of the BFDV among 1,095 individual birds of the 17 psittacine species in Iran followed by analyzing the DNA sequences of seven replication-associated protein (rep) and 10 capsid (cap) genomes of the virus. The BFDV was found to be the foremost pathogen among more than 12 psittacine species, and phylogenetic analysis showed that the BFDV GenBank-published sequences from Poland, Saudi Arabia, South Africa, Taiwan, and Thailand were most similar to those of this study. Evolutionary analysis concluded that arginine, leucine, and glycine were the amino acids frequently involved in the least-conserved substitution patterns of BFDV, and conversely, methionine, glutamine, and tryptophan were the amino acids that exhibited ultra-high conservation through the substitution patterns. The high substitution rate of arginine to lysine and glycine to serine also made greater contribution to the BFDV gene mutation. The relative synonymous codon usage between two genes revealed that the cap genome encoded proteins frequently used fewer codons, while the rep genome encoded proteins used more codons only at moderate frequency, explaining the broader divergence of the cap compared to the rep sequence. The data analysis also introduced a new variant of BFDV that exists in the rep and cap sequences of budgerigars. While the existence of more new variants was suspected, more solid evidence is required to substantiate this suspicion.

Development and applications of a TaqMan based quantitative real-time PCR for the rapid detection of Pigeon circovirus (PiCV)

TaqMan probe based quantitative polymerase reaction (TaqMan qPCR) is a robust and reliable technique for detecting and quantifying target DNA copies. Quantitative molecular diagnosis of genetically diverse single stranded DNA (ssDNA) virus such as Pigeon circovirus (PiCV) can be challenging owing to difficulties in primer binding or low abundance of template DNA copies in clinical specimens. Several methods have been described for the detection of PiCV, being qPCR the most simple and reliable. As far as is known, two qPCR systems described until now are based on SYBR green. This study reports development and validation of a highly sensitive TaqMan qPCR targeted to Rep for the detection of highly diverse PiCV in pigeon samples with excellent reproducibility, specificity, and sensitivity. The limit of detection was determined as low as 2 (two) plasmid copies. Estimations of 100 % specificity and 100 % sensitivity were obtained based on the qPCR results with panel of 60 samples (known PiCV positive, n = 30; known PiCV negative, n = 20; samples positive to Beak and feather disease virus (BFDV), n = 5 and samples positive to canine circovirus, n = 5). Co-efficient of variation (CV) for Ct values ranged between 0.27 % and 0.78 % in the same assay and 1.84-2.87 % in different assays.

Molecular detection and phylogenetic analysis of pigeon circovirus from racing pigeons in Northern China

Background

Pigeon circovirus (PiCV) infections in pigeons (Columba livia) have been reported worldwide. Currently, pigeon racing is becoming increasingly popular and considered to be a national sport in China, and even, the greatest competitions of racing pigeons are taking place in China. However, there are still no epidemiologic data regarding PiCV infections among racing pigeons in China. The purpose of our study was to provide information of prevalence, genetic variation and evolution of PiCV from racing pigeons in China.

Results

To trace the prevalence, genetic variation and evolution of PiCV in sick and healthy racing pigeons, 622 samples were collected from 11 provinces or municipalities in China from 2016 to 2019. The results showed that the positive rate of PiCV was 19.3% (120/622) at the sample level and 59.0% (23/39) at the club level, thus suggesting that the virus was prevalent in Chinese racing pigeons. A sequence analysis revealed that the cap genes of the PiCV strains identified in our study displayed a high genetic diversity and shared nucleotide homologies of 71.9%–100% and amino acid homologies of 71.7%–100%. 28 and 36 unique amino acid substitutions were observed in the Cap and Rep proteins derived from our PiCV strains, respectively. A cladogram representation of PiCV strains phylogeny based on 90 cap gene sequences showed that the strains in this study could be further divided into seven clades (A, B, C, E, G, H, and I) and some of them were closely related to worldwide strains from different types of pigeons. A large number of recombination events (31 events) were also detected in the PiCV genomes from Chinese racing pigeons.

Conclusions

These findings indicate that PiCV strains circulating in China exhibit a high genetic diversity and also contribute to information of prevalence, genetic variation and evolution of PiCV from racing pigeons in China.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08425-8.

Structural Perspectives of Beak and Feather Disease Virus and Porcine Circovirus Proteins

Circoviruses represent a rapidly expanding group of viruses that infect both vertebrate and invertebrate hosts. Members are responsible for diseases of veterinary and economic importance, including postweaning multisystemic wasting syndrome in pigs, and beak and feather disease (BFD) in birds. These viruses are associated with lymphoid depletion and immunosuppressive conditions in infected animals leading to systemic illness. Circoviruses are small nonenveloped DNA viruses containing a single-stranded circular genome, encoding two major proteins: the capsid-associated protein (Cap), comprising the entirety of the viral capsid, and the replication-associated protein (Rep). Cap is the only protein component of the virion and plays crucial roles throughout the virus replication cycle, including viral attachment, cell entry, genome uncoating, and packaging of newly formed viral particles. Rep mediates recognition of replication origin motifs in the viral genome sequence and is responsible for endonuclease activity enabling nicking of the circular DNA and initiation of rolling-circle replication (RCR). Porcine circovirus 2 (PCV2) was the first circovirus capsid structure to be solved at atomic resolution using X-ray crystallography. The structure revealed an assembly comprising 60 monomeric subunits to form virus-like particles. Each Cap monomer harbors a canonical viral jelly roll domain composed of two, four-stranded antiparallel β-sheets. Crystal structures of two distinct macromolecular assemblies from BFD virus Cap were also resolved at high resolution. In these structures, the exposure of the N-terminal arginine-rich motif, responsible for DNA binding and nuclear localization is reversed. Additional structural investigations have also elucidated a PCV2 type-specific neutralizing epitope, and interaction between the PCV2 capsid and polymers such as heparin. In this review, we provide a snapshot of the structural and functional aspects of circovirus proteins.

Is PBFD Simptomatology Species Specific Rather then Strain Specific? – A Case of 8 Lovebirds

Eight lovebirds of both sexes and different age were admitted showing alterations in behaviour and apathy. During the initial examination delamination of the beak was noted in all birds and discrete areas of alopecia in three of eight birds. Based on clinical experience, molecular diagnostic on PBFD, sequencing of obtained amplicons, and histopathological examination were performed. All birds tested positive on the presence of PBFD virus, despite the fact they did not exhibit expected clinical signs for PBFD. Sequencing results showed 100% match with sequences previously isolated from parrots with PBFD exhibiting classical PBFD manifestation. Histopathological examination showed similar findings as in previously described cases of PBFD in parrots. Other studies on psittacine birds correlate clinical manifestations and nucleotide variations with geographic localization. Our results indicate that the clinical manifestation of the disease is more dependent on bird species than on the genetic variation of the virus or the geographical distribution.

Beak and feather disease virus (BFDV) prevalence, load and excretion in seven species of wild caught common Australian parrots

Pathogens pose a major risk to wild host populations, especially in the face of ongoing biodiversity declines. Beak and feather disease virus (BFDV) can affect most if not all members of one of the largest and most threatened bird orders world-wide, the Psittaciformes. Signs of disease can be severe and mortality rates high. Its broad host range makes it a risk to threatened species in particular, because infection can occur via spill-over from abundant hosts. Despite these risks, surveillance of BFDV in locally abundant wild host species has been lacking. We used qPCR and haemagglutination assays to investigate BFDV prevalence, load and shedding in seven abundant host species in the wild in south-east Australia: Crimson Rosellas (Platycercus elegans), Eastern Rosellas (Platycercus eximius), Galahs (Eolophus roseicapillus), Sulphur-crested Cockatoos (Cacatua galerita), Blue-winged Parrots (Neophema chrysostoma), Rainbow Lorikeets (Trichoglossus moluccanus) and Red-rumped Parrots (Psephotus haematonotus). We found BFDV infection in clinically normal birds in six of the seven species sampled. We focused our analysis on the four most commonly caught species, namely Crimson Rosellas (BFDV prevalence in blood samples: 41.8%), Sulphur-crested Cockatoos (20.0%), Blue-winged Parrots (11.8%) and Galahs (8.8%). Species, but not sex, was a significant predictor for BFDV prevalence and load. 56.1% of BFDV positive individuals were excreting BFDV antigen into their feathers, indicative of active viral replication with shedding. Being BFDV positive in blood samples predicted shedding in Crimson Rosellas. Our study confirms that BFDV is endemic in our study region, and can inform targeted disease management by providing comparative data on interspecies variation in virus prevalence, load and shedding.

Prevalence of Aves Polyomavirus 1 and Beak and Feather Disease Virus From Exotic Captive Psittacine Birds in Chile

Avian polyomavirus disease and psittacine beak and feather disease (PBFD) are both contagious viral diseases in psittacine birds with similar clinical manifestations and characterized by abnormal feathers. To determine the prevalence of Aves polyomavirus 1 (APyV) and beak and feather disease virus (BFDV) in captive, exotic psittacine birds in Chile, feathers from 250 psittacine birds, representing 17 genera, were collected and stored during the period 2013-2016. Polymerase chain reaction testing was used to detect APyV and BFDV were detected in feather bulb samples. The results indicated that 1.6% (4/250) of the samples were positive for APyV, 23.2% (58/250) were positive to BFDV, and 0.8% (2/250) were positive to both APyV and BFDV. This is the first report, to our knowledge, of APyV and BFDV prevalence in captive, exotic psittacine birds in South America. Analysis of 2 Chilean partial sequences of the gene encoding agnoprotein 1a (APyV) and the replication-associated protein (BFDV) extends the knowledge of genomic variability for both APyV and BFDV isolates and their spectrum of hosts. No geographical marker was detected for the local isolates.

Disease surveillance in wild Victorian cacatuids reveals co-infection with multiple agents and detection of novel avian viruses

Wild birds are known reservoirs of bacterial and viral pathogens, some of which have zoonotic potential. This poses a risk to both avian and human health, since spillover into domestic bird populations may occur. In Victoria, wild-caught cockatoos trapped under licence routinely enter commercial trade. The circovirus Beak and Feather Disease Virus (BFDV), herpesviruses, adenoviruses and Chlamydia psittaci have been identified as significant pathogens of parrots globally, with impacts on both aviculture and the conservation efforts of endangered species. In this study, we describe the results of surveillance for psittacid herpesviruses (PsHVs), psittacine adenovirus (PsAdV), BFDV and C. psittaci in wild cacatuids in Victoria, Australia. Samples were collected from 55 birds of four species, and tested using genus or family-wide polymerase chain reaction methods coupled with sequencing and phylogenetic analyses for detection and identification of known and novel pathogens. There were no clinically observed signs of illness in most of the live birds in this study (96.3%; n = 53). Beak and Feather Disease Virus was detected with a prevalence of 69.6% (95% CI 55.2-80.9). Low prevalences of PsHV (1.81%; 95% CI 0.3-9.6), PsAdV (1.81%; 95% CI 0.3-9.6), and C. psittaci (1.81%; 95% CI 0.3-9.6) was detected. Importantly, a novel avian alphaherpesvirus and a novel avian adenovirus were detected in a little corella (Cacatua sanguinea) co-infected with BFDV and C. psittaci. The presence of multiple potential pathogens detected in a single bird presents an example of the ease with which such infectious agents may enter the pet trade and how novel viruses circulating in wild populations have the potential for transmission into captive birds. Genomic identification of previously undescribed avian viruses is important to further our understanding of their epidemiology, facilitating management of biosecurity aspects of the domestic and international bird trade, and conservation efforts of vulnerable species.

Identification and characterization of novel genotypes of psittacine beak and feather disease virus from budgerigar in China

Psittacine beak and feather disease (PBFD) is a common disease in psittacine bird that caused by beak and feather disease virus (BFDV). BFDV is widely spread and threatening psittacine birds worldwide. However, the BFDV infection in China remains largely unknown. In this study, a surveillance study of BFDV was conducted in three budgerigar breeding facilities, which showed that 66.6% of collected faeces samples were positive for BFDV. Full genomes of nine BFDV circulating in the three budgerigar breeding facilities (three for each facility) were determined and analysed. The full genomes shared 75.9% to 87.5% identity with the known genotype BFDV. Phylogenetic analysis of the full genome indicated that the BFDV circulating in China formed a separated group, and the nine isolates fell into three subgroups, suggesting that different unique BFDV genotypes are circulating in China. Notably, the Cap genes of three strains (SD3, SD5 and SD9) showed low identity (67.9% to 70%) to all the known genotypes of BFDV. Phylogenetic analysis showed that these three Cap genes formed a unique lineage that is different from all known genotypes, which suggested that the SD3, SD5 and SD9 strains identified in this study belong to a novel genotype that has not been reported. However, the origin of this genotype remains unclear. All the data indicated that the different unique genotypes of BFDV are co-circulating in China, and active surveillance of BFDV is warranted.

Beak and feather disease virus carriage by Knemidocoptes pilae in a sulphur-crested cockatoo (Cacatua galerita)

BACKGROUND

This paper describes the pathology associated with psittacine beak and feather disease in a wild sulphur-crested cockatoo with concurrent knemidocoptic mange, cestodiasis and mycotic encephalitis.

METHODS & RESULTS

Large numbers of Knemidocoptes pilae Lavoipierre and Griffiths, 1951 (Acari: Epidermoptidae, Knemidokoptinae) were identified in affected skin associated with enhanced expression of beak and feather disease virus (BFDV) determined by immunohistochemistry. Also, BFDV antigen was demonstrated in high concentration in the gut and faecal sacs of mites, raising the possibility of ectoparasites as fomites and vectors of BFDV transmission. Large numbers of Raillietina spp. cestodes were present in the intestines. Within the brain there was a focally extensive region of necrosis and inflammation associated with branching, septate, pigmented hyphae consistent with zygomycete fungal infection.

CONCLUSION

This case highlights the potential immunosuppressive effects of BFDV infection and its potential as a keystone pathogen in the Australian environment.

Full-Genome Sequence of Porcine Circovirus type 3 recovered from serum of sows with stillbirths in Brazil

Two full-genome sequences of porcine circovirus type 3 (PCV3) are reported. The genomes were recovered from pooled serum samples from sows who had just delivered litters with variable numbers of stillbirths. The two circular genomes (PCV3-BR/RS/6 and PCV3-BR/RS/8) are 2,000 nucleotides long and contain two open reading frames (ORFs) oriented in opposite directions that encode the putative capsid (Cap) and replicase (Rep) proteins. The intergenic region contains a stem-loop motif, as reported for other circoviruses. Rolling circle replication motifs and putative helicase domains were identified in the Rep coding region. The degree of overall nucleotide similarity between the genomes reported here and those available at GenBank was higher than 97%. No PCV3 sequence was detected in pooled serum samples from sows which had no stillbirths on the same farms. However, further studies are necessary to confirm the association between PCV3 and the occurrence of stillbirths.

Recombinant expression of beak and feather disease virus capsid protein and assembly of virus-like particles in Nicotiana benthamiana

BACKGROUND

Beak and feather disease virus (BFDV) is an important disease causing agent affecting psittacines. BFDV is highly infectious and can present as acute, chronic or subclinical disease. The virus causes immunodeficiency and is often associated with secondary infections. No commercial vaccine is available and yields of recombinant BFDV capsid protein (CP) expressed in insect cells and bacteria are yet to be seen as commercially viable, although both systems produced BFDV CP that could successfully assemble into virus-like particles (VLPs). Plants as expression systems are increasingly becoming favourable for the production of region-specific and niche market products. The aim of this study was to investigate the formation and potential for purification of BFDV VLPs in Nicotiana benthamiana.

METHODS

The BFDV CP was transiently expressed in N. benthamiana using an Agrobacterium-mediated system and plant expression vectors that included a bean yellow dwarf virus (BeYDV)-based replicating DNA vector. Plant-produced BFDV CP was detected using immunoblotting. VLPs were purified using sucrose cushion and CsCl density gradient centrifugation and visualised using transmission electron microscopy.

RESULTS

In this study we demonstrate that the BFDV CP can be successfully expressed in N. benthamiana, albeit at relatively low yield. Using a purification strategy based on centrifugation we demonstrated that the expressed CP can self-assemble into VLPs that can be detected using electron microscopy. These plant-produced BFDV VLPs resemble those produced in established recombinant expression systems and infectious virions. It is possible that the VLPs are spontaneously incorporating amplicon DNA produced from the replicating BeYDV plant vector.

CONCLUSIONS

This is the first report of plant-made full-length BFDV CP assembling into VLPs. The putative pseudovirions could be used to further the efficacy of vaccines against BFDV.

A Novel Porcine Circovirus Distantly Related to Known Circoviruses Is Associated with Porcine Dermatitis and Nephropathy Syndrome and Reproductive Failure

Porcine circovirus-associated disease (PCVAD) is clinically manifested by postweaning multisystemic wasting syndrome (PMWS), respiratory and enteric disease, reproductive failure, and porcine dermatitis and nephropathy syndrome (PDNS). Porcine circovirus 2 (PCV2) is an essential component of PCVAD, although an etiologic role in PDNS is not well established. Here, a novel circovirus, designated porcine circovirus 3 (PCV3), was identified in sows that died acutely with PDNS-like clinical signs. The capsid and replicase proteins of PCV3 are only 37% and 55% identical to PCV2 and bat circoviruses, respectively. Aborted fetuses from sows with PDNS contained high levels of PCV3 (7.57 × 10⁷ genome copies/ml), and no other viruses were detected by PCR and metagenomic sequencing. Immunohistochemistry (IHC) analysis of sow tissue samples identified PCV3 antigen in skin, kidney, lung, and lymph node samples localized in typical PDNS lesions, including necrotizing vasculitis, glomerulonephritis, granulomatous lymphadenitis, and bronchointerstitial pneumonia. Further study of archived PDNS tissue samples that were negative for PCV2 by IHC analysis identified 45 of 48 that were PCV3 positive by quantitative PCR (qPCR), with 60% of a subset also testing positive for PCV3 by IHC analysis. Analysis by qPCR of 271 porcine respiratory disease diagnostic submission samples identified 34 PCV3-positive cases (12.5%), and enzyme-linked immunosorbent assay detection of anti-PCV3 capsid antibodies in serum samples found that 46 (55%) of 83 samples tested were positive. These results suggest that PCV3 commonly circulates within U.S. swine and may play an etiologic role in reproductive failure and PDNS. Because of the high economic impact of PCV2, this novel circovirus warrants further studies to elucidate its significance and role in PCVAD.

IMPORTANCE

While porcine circovirus 2 (PCV2) was first identified in sporadic cases of postweaning multisystemic wasting syndrome in Canada in the early 1990s, an epidemic of severe systemic disease due to PCV2 spread worldwide in the ensuing decade. Despite being effectively controlled by commercial vaccines, PCV2 remains one of the most economically significant viruses of swine. Here, a novel porcine circovirus (PCV3) that is distantly related to known circoviruses was identified in sows with porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCV2, which has previously been associated with these clinical presentations, was not identified. High levels of PCV3 nucleic acid were observed in aborted fetuses by quantitative PCR, and PCV3 antigen was localized in histologic lesions typical of PDNS in sows by immunohistochemistry (IHC) analysis. PCV3 was also identified in archival PDNS diagnostic samples that previously tested negative for PCV2 by IHC analysis. The emergence of PCV3 warrants further investigation.

Review of psittacine beak and feather disease and its effect on Australian endangered species

BACKGROUND

Since it was first described in the early 1980s, psittacine beak and feather disease (PBFD) has become recognised as the dominant viral pathogen of psittacine birds in Australia. Our aim was to evaluate and review the effect of PBFD and its position as a key threatening process to Australian psittacine bird species. We review the origin/evolutionary pathways and potential threat of PBFD to endangered psittacine bird populations and captive-breeding flocks.

CONCLUSIONS

The most recent beak and feather disease virus (BFDV) phylogenetic analyses indicate that all endangered Australian psittacine bird species are susceptible to, and equally likely to be infected by, BFDV genotypes from a range of host psittacine species. Management of the disease in captive-breeding programs has relied on testing and culling, which has proven costly. The risk of PBFD should be considered very carefully by management teams contemplating the establishment of captive-breeding flocks for endangered species. Alternative disease prevention tools, including vaccination, which are increasingly being used in wildlife health, should be considered more seriously for managing and preventing PBFD in captive flocks of critically endangered species.

Whole-Genome Sequence of a Beak and Feather Disease Virus Isolate from a Fledgling Red-Capped Parrot (Purpureicephalus spurius)

The complete genome sequence of beak and feather disease virus (BFDV) from a fledgling red-capped parrot (Purpureicephalus spurius) was assembled and characterized. The genome consists of 1,995 nucleotides and encodes two major proteins in opposing directions. This is the first evidence of BFDV infectivity and a complete genome sequence for this novel host.

Characterization of Beak and Feather Disease Virus Genomes from Wild Musk Lorikeets (Glossopsitta concinna)

Three complete genomes of beak and feather disease virus (BFDV) were recovered from wild musk lorikeets (Glossopsitta concinna). The genomes consisted of 2,008 to 2,010 nucleotides (nt) and encode two major proteins transcribing in opposing directions. This is the first report of BFDV complete genome sequences obtained from this host species.

Molecular Characterization of a Beak and Feather Disease Virus Genome from a Purple Crowned Lorikeet (Glossopsitta porphyrocephala)

The complete genome sequence of beak and feather disease virus (BFDV) from a purple crowned lorikeet (Glossopsitta porphyrocephala) was characterized. The genome consists of 2,010 nucleotides and encodes replicase-associated protein and capsid protein. This is the first evidence of BFDV infectivity and complete genome sequence for this novel host.

A comparison of PCR assays for beak and feather disease virus and high resolution melt (HRM) curve analysis of replicase associated protein and capsid genes

Beak and feather disease virus (BFDV) threatens a wide range of endangered psittacine birds worldwide. In this study, we assessed a novel PCR assay and genetic screening method using high-resolution melt (HRM) curve analysis for BFDV targeting the capsid (Cap) gene (HRM-Cap) alongside conventional PCR detection as well as a PCR method that targets a much smaller fragment of the virus genome in the replicase initiator protein (Rep) gene (HRM-Rep). Limits of detection, sensitivity, specificity and discriminatory power for differentiating BFDV sequences were compared. HRM-Cap had a high positive predictive value and could readily differentiate between a reference genotype and 17 other diverse BFDV genomes with more discriminatory power (genotype confidence percentage) than HRM-Rep. Melt curve profiles generated by HRM-Cap correlated with unique DNA sequence profiles for each individual test genome. The limit of detection of HRM-Cap was lower (2×10^-5ng/reaction or 48 viral copies) than that for both HRM-Rep and conventional BFDV PCR which had similar sensitivity (2×10^-6ng or 13 viral copies/reaction). However, when used in a diagnostic setting with 348 clinical samples there was strong agreement between HRM-Cap and conventional PCR (kappa=0.87, P<0.01, 98% specificity) and HRM-Cap demonstrated higher specificity (99.9%) than HRM-Rep (80.3%).

Beak and feather disease virus in wild and captive parrots: an analysis of geographic and taxonomic distribution and methodological trends

Psittacine beak and feather disease (PBFD) has emerged in recent years as a major threat to wild parrot populations and is an increasing concern to aviculturists and managers of captive populations. Pathological and serological tests for screening for the presence of beak and feather disease virus (BFDV) are a critical component of efforts to manage the disease and of epidemiological studies. Since the disease was first reported in the mid-1970s, screening for BFDV has been conducted in numerous wild and captive populations. However, at present, there is no current and readily accessible synthesis of screening efforts and their results. Here, we consolidate information collected from 83 PBFD- and BFDV-based publications on the primary screening methods being used and identify important knowledge gaps regarding potential global disease hotspots. We present trends in research intensity in this field and critically discuss advances in screening techniques and their applications to both aviculture and to the management of threatened wild populations. Finally, we provide an overview of estimates of BFDV prevalence in captive and wild flocks alongside a complete list of all psittacine species in which the virus has been confirmed. Our evaluation highlights the need for standardised diagnostic tests and more emphasis on studies of wild populations, particularly in view of the intrinsic connection between global trade in companion birds and the spread of novel BFDV strains into wild populations. Increased emphasis should be placed on the screening of captive and wild parrot populations within their countries of origin across the Americas, Africa and Asia.

Survey of captive parrot populations around Port Phillip Bay, Victoria, Australia, for psittacine beak and feather disease virus, avian polyomavirus and psittacine adenovirus

OBJECTIVE

This study investigated the prevalence of psittacine beak and feather disease virus (BFDV), avian polyomavirus (APV) and psittacine adenovirus (PsAdV) in captive psittacine birds around Port Phillip Bay, Victoria, Australia.

METHODS

Samples of fresh droppings were collected from 118 psittacine birds (109 clinically normal and 9 with feather abnormalities) from 11 avaries in different locations and were used for detection of BFDV, APV and PsAdV using PCR.

RESULTS

BFDV, APV and PsAdV were detected in 31%, 13% and 4%, respectively, of the specimens tested. One budgerigar was found to be co-infected with BFDV and PsAdV. At least one sample tested positive for BFDV at each location.

CONCLUSION

This is the first report of the prevalence of BFDV, APV and PsAdV in Victoria and provides a foundation for future studies examining the influence of these viruses on the health of aviary birds in Victoria.

Evidence of a deep viral host switch event with beak and feather disease virus infection in rainbow bee-eaters (Merops ornatus)

Since the characterization of psittacine beak and feather disease (PBFD) in 1984, a wide range of avian circoviruses have been discovered with varying pathogenic effects amongst a diverse range of avian hosts. Until recently these circovirus species were thought to be restricted to within avian Orders such as the Psittaciformes for beak and feather disease virus (BFDV) and Columbiformes for pigeon circovirus with little evidence of cross-family transmission or replication. We report evidence of a naturally occurring novel host switch event with self-limiting BFDV infection in a group of rainbow bee-eaters (Merops ornatus) a species of Coraciiformes unrelated to parrots and not previously known to be susceptible to any avian circovirus. The outbreak highlights important and unexpected aspects of disease emergence and host-switching pertinent to other situations when viruses might cross species boundaries as well as the potential of avian circoviruses to infect disparate host species.

Genome Sequences of Beak and Feather Disease Virus in Urban Rainbow Lorikeets (Trichoglossus haematodus)

Beak and feather disease viral genomes were recovered from two deceased juvenile urban rainbow lorikeets (Trichoglossus haematodus) that lacked tail feathers. These genomes share ~95% pairwise identity with two beak and feather disease virus (BFDV) genomes identified in wild and captive Australian T. haematodus birds and ~92% identity to those in wild New Caledonian T. haematodus deplanchii birds.

Prevalence of beak and feather disease virus in wild Platycercus elegans: comparison of three tissue types using a probe-based real-time qPCR test

The detection of avian viruses in wild populations has considerable conservation implications. For DNA-based studies, feathers may be a convenient sample type for virus screening and are, therefore, an increasingly common technique. This is despite recent concerns about DNA quality, ethics, and a paucity of data comparing the reliability and sensitivity of feather sampling to other common sample types such as blood. Alternatively, skeletal muscle tissue may offer a convenient sample to collect from dead birds, which may reveal viraemia. Here, we describe a probe-based quantitative real-time PCR for the relative quantification of beak and feather disease virus (BFDV), a pathogen of serious conservation concern for parrots globally. We used this method to test for BFDV in wild crimson rosellas (Platycercus elegans), and compared three different sample types. We detected BFDV in samples from 29 out of 84 individuals (34.5%). However, feather samples provided discordant results concerning virus presence when compared with muscle tissue and blood, and estimates of viral load varied somewhat between different sample types. This study provides evidence for widespread infection of BFDV in wild crimson rosellas, but highlights the importance of sample type when generating and interpreting qualitative and quantitative avian virus data.

Molecular Characterization of Genome Sequences of Beak and Feather Disease Virus from the Australian Twenty-Eight Parrot (Barnardius zonarius semitorquatus)

Three complete genomes of beak and feather disease virus (BFDV) were recovered from wild twenty-eight parrots (Polytelis anthopeplus monarchoides). The genomes consisted of 1,996 bp with 1,934 identical sites and a typically content stem-loop structure between ORF1 and ORF2. This is the first report of BFDV infection as well as the complete genome sequences for this host species globally.

Phylogenetic analysis of beak and feather disease virus across a host ring-species complex

Pathogens have been hypothesized to play a major role in host diversity and speciation. Susceptibility of hybrid hosts to pathogens is thought to be a common phenomenon that could promote host population divergence and subsequently speciation. However, few studies have tested for pathogen infection across animal hybrid zones while testing for codivergence of the pathogens in the hybridizing host complex. Over 8 y, we studied natural infection by a rapidly evolving single-strand DNA virus, beak and feather diseases virus (BFDV), which infects parrots, exploiting a host-ring species complex (Platycercus elegans) in Australia. We found that host subspecies and their hybrids varied strikingly in both BFDV prevalence and load: both hybrid and phenotypically intermediate subspecies had lower prevalence and load compared with parental subspecies, while controlling for host age, sex, longitude and latitude, as well as temporal effects. We sequenced viral isolates throughout the range, which revealed patterns of genomic variation analogous to Mayr's ring-species hypothesis, to our knowledge for the first time in any host-pathogen system. Viral phylogeny, geographic location, intraspecific host density, and parrot community diversity and composition did not explain the differences in BFDV prevalence or load between subpopulations. Overall, our analyses suggest that functional host responses to infection, or force of infection, differ between subspecies and hybrids. Our findings highlight the role of host hybridization and clines in altering host-pathogen interactions, dynamics that can have important implications for models of speciation with gene flow, and offer insights into how pathogens may adapt to diverging host populations.

Beak and feather disease viruses circulating in Cape parrots (Poicepahlus robustus) in South Africa

Captive and wild psittacines are vulnerable to the highly contagious psittacine beak and feather disease. The causative agent, beak and feather disease virus (BFDV), was recently detected in the largest remaining population of endangered Cape parrots (Poicepahlus robustus), which are endemic to South Africa. Full-length genomes were isolated and sequenced from 26 blood samples collected from wild and captive Cape parrots to determine possible origins of infection. All sequences had characteristic BFDV sequence motifs and were similar in length to those described in the literature. However, BFDV coat protein (CP) sequences from this study did not contain a previously identified bipartite nuclear localisation signal (NLS) within residues 39-56, which indicates that an alternate NLS is involved in shuttling the CP into the nucleus. Sequences from the wild population shared a high degree of similarity, irrespective of year or location, suggesting that the disease outbreak occurred close to the time when the samples were collected. Phylogenetic analysis of full-length genomes showed that the captive Cape parrot sequences cluster with those isolated from captive-bred budgerigars in KwaZulu-Natal Province, South Africa. Exposure to captive-bred Cape parrots from a breeding facility in KwaZulu-Natal is suggested as a possible source for the virus infection. Phylogenetic analysis of BFDV isolates from wild and captive Cape parrots indicated two separate infection events in different populations, which highlights the potential risk of introducing new strains of the virus into the wild population. The present study represents the first systematic investigation of BFDV virus diversity in the southern-most population of Cape parrots.

Beak and feather disease virus: correlation between viral load and clinical signs in wild Cape parrots (Poicepahlus robustus) in South Africa

Psittacine beak and feather disease (PBFD), the most prevalent viral disease affecting psittacines, is caused by beak and feather disease virus (BFDV). This study assessed viral load using qPCR in a wild Cape parrot population affected by PBFD and compared it to overall physical condition based on clinical signs attributable to PBFD. A significant inverse correlation between viral load and overall physical condition was found, which confirmed that clinical signs may confidently be used to diagnose the relative severity of BFDV infections in wild populations. This is the first assessment of BFDV viral load in a wild psittacine population.

Characterization of the Whole-Genome Sequence of a Beak and Feather Disease Virus Isolate from a Mallee Ringneck Parrot (Barnardius zonarius barnardi)

The complete genome sequence of beak and feather disease virus (BFDV) from a wild Australian Mallee ringneck parrot (Barnardius zonarius barnardi) was characterized. The genome consists of 1,995 nucleotides and encodes two major proteins in opposing directions. This is the first evidence of BFDV infectivity and the first complete genome sequence for this novel host.

Molecular analysis and associated pathology of beak and feather disease virus isolated in Italy from young Congo African grey parrots (Psittacus erithacus) with an "atypical peracute form" of the disease

This study is the first report on the genetic and pathogenic characterization of beak and feather disease virus (BFDV) occurring in Italy. Twenty BFDV strains isolated in Italy from juvenile Congo African grey parrots (Psittacus erithacus) were investigated. Seventeen strains showed an "atypical peracute form" (aPF) of the disease, and three a chronic form (CF). The birds with aPF had been weaned, were independent as far as food and protection were concerned and apparently were without lesions. The gene coding for the putative coat protein was amplified in all isolates while the BFDV genome was sequenced completely in 10 samples, eight of them belonging to aPF affected birds and two from CF of the disease. All full genomes clustered into the J strain of BFDV, where two new subtypes were identified. Recombination analyses showed evidence of genetic exchanges in two BFDV genomes. In addition, a correlation between viral isolate and origin of the breeding material was shown, while an association between the genetic features of the virus and the clinical form was not observed. Histologically, apoptosis was detected frequently in aPF samples and sporadically in CF samples. Interestingly, BFDV antigens were detected in the nuclei and cytoplasm of such apoptotic cells. The data presented here support the hypothesis that, in the absence of a defined BFDV genetic variant accountable for a specific clinical form of psittacine beak and feather disease, differences in the apoptotic rate between aPF and CF are strictly host related.

Phylogeny of beak and feather disease virus in cockatoos demonstrates host generalism and multiple-variant infections within Psittaciformes

Phylogenetic analyses of the highly genetically diverse but antigenically conserved, single-stranded circular, DNA genome of the avian circovirus, beak and feather disease virus (BFDV) from cockatoo species throughout Australia demonstrated a high mutation rate for BFDV (orders of magnitude fall in the range of 10(-4) substitutions/site/year) along with strong support for recombination indicating active cross-species transmission in various subpopulations. Multiple variants of BFDV were demonstrated with at least 30 genotypic variants identified within nine individual birds, with one containing up to 7 variants. Single genetic variants were detected in feathers from 2 birds but splenic tissue provided further variants. The rich BFDV genetic diversity points to Australasia as the most likely geographical origin of this virus and supports flexible host switching. We propose this as evidence of Order-wide host generalism in the Psittaciformes characterised by high mutability that is buffered by frequent recombination and slow replication strategy.

Whole-Genome Sequence Characterization of a Beak and Feather Disease Virus in a Wild Regent Parrot (Polytelis anthopeplus monarchoides)

The whole-genome sequence of beak and feather disease virus (BFDV) from a wild Australian regent parrot (Polytelis anthopeplus monarchoides) was characterized. The genome consists of 1,993 bp and has a typical stem-loop structure between open reading frame 1 (ORF1) and ORF2. This is the first evidence of BFDV infection as well as the complete genome sequence for this host species, globally.

Mutability dynamics of an emergent single stranded DNA virus in a naïve host

Quasispecies variants and recombination were studied longitudinally in an emergent outbreak of beak and feather disease virus (BFDV) infection in the orange-bellied parrot (Neophema chrysogaster). Detailed health monitoring and the small population size (<300 individuals) of this critically endangered bird provided an opportunity to longitudinally track viral replication and mutation events occurring in a circular, single-stranded DNA virus over a period of four years within a novel bottleneck population. Optimized PCR was used with different combinations of primers, primer walking, direct amplicon sequencing and sequencing of cloned amplicons to analyze BFDV genome variants. Analysis of complete viral genomes (n = 16) and Rep gene sequences (n = 35) revealed that the outbreak was associated with mutations in functionally important regions of the normally conserved Rep gene and immunogenic capsid (Cap) gene with a high evolutionary rate (3.41×10⁻³ subs/site/year) approaching that for RNA viruses; simultaneously we observed significant evidence of recombination hotspots between two distinct progenitor genotypes within orange-bellied parrots indicating early cross-transmission of BFDV in the population. Multiple quasispecies variants were also demonstrated with at least 13 genotypic variants identified in four different individual birds, with one containing up to seven genetic variants. Preferential PCR amplification of variants was also detected. Our findings suggest that the high degree of genetic variation within the BFDV species as a whole is reflected in evolutionary dynamics within individually infected birds as quasispecies variation, particularly when BFDV jumps from one host species to another.

Whole-Genome Sequences of Two Beak and Feather Disease Viruses in the Endangered Swift Parrot (Lathamus discolor)

Two complete genomes of beak and feather disease virus (BFDV) were characterized from Lathamus discolor, the Australian swift parrot. This is the first report of BFDV complete genome sequences in this host. The completed BFDV genomes consist of 1,984 nucleotides encoding two open reading frames with 99.7% pairwise nucleotide identity.

Differential expression of two isolates of beak and feather disease virus capsid protein in Escherichia coli

Expression of recombinant beak and feather disease virus (BFDV) capsid-associated protein (Cap) has relied on inefficient techniques that typically produce low yields or use specialized expression systems, which greatly increase the cost and expertise required for mass production. An Escherichia coli system was used to express recombinant BFDV Cap derived from two isolates of BFDV, from a Long-billed Corella (Cacatua tenuirostris) and an Orange-bellied parrot (OBP; Neophema chrysogaster). Purification by affinity and size exclusion chromatography was optimized through an iterative process involving screening and modification of buffer constituents and pH. A buffer containing glycerol, β-mercaptoethanol, Triton X-100, and a high concentration of NaCl at pH 8 was used to increase solubility of the protein. The final concentration of the corella-isolated BFDV protein was fifteen- to twenty-fold greater than that produced in previous publications using E. coli expression systems. Immunoassays were used to confirm the specific antigenicity of recombinant Cap, verifying its validity for use in continued experimentation as a potential vaccine, a reagent in diagnostic assays, and as a concentrated sample for biological discoveries.

Molecular characterisation of beak and feather disease virus (BFDV) in New Zealand and its implications for managing an infectious disease

Beak and feather disease virus (BFDV) infections are often fatal to both captive and wild parrot populations. Its recent discovery in a wild population of native red-fronted parakeets has raised concerns for the conservation of native parrots, all of which are threatened or endangered. The question of a recent introduction versus a native genotype of the virus poses different conservation-management challenges, and thus, a clear understanding of the molecular phylogeny of BDFV is a crucial step towards integrated management planning. This study represents the first comprehensive attempt to screen New Zealand's endangered and threatened psittacines systematically for BFDV. We sampled and screened kakapos (Strigops habroptilus), kakas (Nestor meridionalis), keas (N. notabilis), Chatham parakeets (Cyanoramphus forbesi), Malherbe's parakeets (Cyanoramphus malherbi), yellow-crowned parakeets (C. auriceps) and red-fronted parakeets (Cyanoramphus novaezelandiae), as well as eastern rosellas (Platycercus eximius), an introduced species that is now common throughout the North Island, for BFDV. Out of all species and populations sampled (786 individuals), we found 16 BFDV-positive red-fronted parakeets from Little Barrier Island/Hauturu, seven eastern rosellas from the Auckland region, and eight yellow-crowned parakeets from the Eglinton Valley in the South Island. The full genomes of the viral isolates from the red-fronted parakeets share 95-97 % sequence identity to those from the invasive eastern rosellas and 92.7-93.4 % to those isolates from the South Island yellow-crowned parakeets. The yellow-crowned parakeet BFDV isolates share 92-94 % sequence identity with those from eastern rosellas. The low level of diversity among all BFDV isolates from red-fronted parakeets could suggest a more recent infection among these birds compared to the yellow-crowned parakeets, whereas the diversity in the eastern rosellas indicates a much more established infection. Pro-active screening and monitoring of BFDV infection rates in aviaries as well as in wild populations are necessary to limit the risk of transmission among threatened and endangered parrot populations in New Zealand.

Tracking viral evolution during a disease outbreak: the rapid and complete selective sweep of a circovirus in the endangered Echo parakeet

Circoviruses are among the smallest and simplest of all viruses, but they are relatively poorly characterized. Here, we intensively sampled two sympatric parrot populations from Mauritius over a period of 11 years and screened for the circovirus Beak and feather disease virus (BFDV). During the sampling period, a severe outbreak of psittacine beak and feather disease, which is caused by BFDV, occurred in Echo parakeets. Consequently, this data set presents an ideal system for studying the evolution of a pathogen in a natural population and to understand the adaptive changes that cause outbreaks. Unexpectedly, we discovered that the outbreak was most likely caused by changes in functionally important regions of the normally conserved replication-associated protein gene and not the immunogenic capsid. Moreover, these mutations were completely fixed in the Echo parakeet host population very shortly after the outbreak. Several capsid alleles were linked to the replication-associated protein outbreak allele, suggesting that whereas the key changes occurred in the latter, the scope of the outbreak and the selective sweep may have been influenced by positive selection in the capsid. We found evidence for viral transmission between the two host populations though evidence for the invasive species as the source of the outbreak was equivocal. Finally, the high evolutionary rate that we estimated shows how rapidly new variation can arise in BFDV and is consistent with recent results from other small single-stranded DNA viruses.

Global genetic diversity and geographical and host-species distribution of beak and feather disease virus isolates

Psittacine beak and feather disease (PBFD) has a broad host range and is widespread in wild and captive psittacine populations in Asia, Africa, the Americas, Europe and Australasia. Beak and feather disease circovirus (BFDV) is the causative agent. BFDV has an ∼2 kb single stranded circular DNA genome encoding just two proteins (Rep and CP). In this study we provide support for demarcation of BFDV strains by phylogenetic analysis of 65 complete genomes from databases and 22 new BFDV sequences isolated from infected psittacines in South Africa. We propose 94% genome-wide sequence identity as a strain demarcation threshold, with isolates sharing >94% identity belonging to the same strain, and strain subtypes sharing >98% identity. Currently, BFDV diversity falls within 14 strains, with five highly divergent isolates from budgerigars probably representing a new species of circovirus with three strains (budgerigar circovirus; BCV-A, -B and -C). The geographical distribution of BFDV and BCV strains is strongly linked to the international trade in exotic birds; strains with more than one host are generally located in the same geographical area. Lastly, we examined BFDV and BCV sequences for evidence of recombination, and determined that recombination had occurred in most BFDV and BCV strains. We established that there were two globally significant recombination hotspots in the viral genome: the first is along the entire intergenic region and the second is in the C-terminal portion of the CP ORF. The implications of our results for the taxonomy and classification of circoviruses are discussed.

Phylogenetic analysis of six isolates of beak and feather disease virus from African grey parrots in Portugal

Beak and feather disease virus (BFDV), a member of the genus Circovirus, was detected in six dead African grey parrots (Psittacus erithacus) in Portugal. The complete nucleotide sequences of these six BFDVs (PT05, PT08, PT08-2, PT08-3, PT09, and PT09-2) were determined and analyzed. The seven open reading frames (ORFs) described for other BFDVs were detected in all strains, except for PT05 and PT08, in which ORFs 4 and 7 are absent. Bayesian inference of phylogeny based on complete genomes of BFDVs isolated in Portugal and 32 other BFDVs found in other parts of the world revealed that PT05 is included in lineage IV, whereas the others form a new proposed genotype lineage IX. The nucleotide diversity ranged from 2% to 12% between the BFDV strains isolated in Portugal and other BFDVs found worldwide.