Avian Bornavirus Research—A Comprehensive Review

Research Note: Development of a reverse transcriptase recombinase-aided amplification method for detection of Parrot Borna Virus 4

The Parrot Borna virus 4 (PaBV-4) is the primary causative agent of parrot developmental disorder (PDD), leading to symptoms such as bloating, undigested feed in stool, decreased appetite, diarrhea, and weight loss. Its impact on the parrot industry has been significant, therefore, it is imperative to develop a rapid detection method for PaBV-4. The detection of PaBV-4 was achieved through the development of an RT-RAA assay, which involved the design of specific probes and primers targeting the N gene. This method allows for detection at 41°C within 30 min and has a minimum detection threshold of 8.56 × 101 copies/μL. The RT-RAA method demonstrated specific detection of PaBV-4 without any cross-reactivity observed with H5N6, H7N9, H9N2 avian influenza virus, newcastle disease virus (NDV), avian infectious bronchitis virus (IBV) and Parrot Borna virus 2 (PaBV-2). The coefficient of variation for the 3 repeatability experiments was below 10%. Tissue samples from 28 suspected cases of PaBV related deaths in parrots were analyzed using both RT-RAA and RT-qPCR methods. The sensitivity and specificity of both methods were 100%, demonstrating perfect agreement between them as indicated by a kappa value of 1. In conclusion, this study created a RT-RAA method for PaBV-4 detection successfully.

Distribution of lesions in psittacine birds naturally infected with parrot bornavirus in Japan

Mononuclear cell infiltration of the central nervous system and ganglioneuritis are characteristic histopathological findings of proventricular dilatation disease (PDD) caused by parrot bornavirus (PaBV) infection. The purpose of this study was to clarify the link between the degree of inflammatory lesions and the distribution of the virus antigen in naturally PaBV-infected parrots. Pathological examination was performed on 18 PaBV-infected birds identified by reverse transcriptase-PCR. Dilatation of the crop, proventriculus, and ventriculus was observed in all 18 (100%) birds, and dilation of the right ventricle of the heart was observed in 14/18 (78%) birds. Cases were classified based on the scores for the distribution and degree of histological lesions into neural type, with severe brain lesions, digestive type, with severe gastric lesions, or nervous/digestive type, with severe lesions in both the brain and ventriculus. The PaBV immunohistological score correlated with the inflammatory lesion scores. Ganglioneuritis, myocarditis, and myocardial degeneration were frequently observed in the heart. Interestingly, macroscopic and microscopic lesions and virus antigen were detected in the hearts of all three histological types. The present study showed that parrots naturally infected with PaBVs can be grouped into three types based on the lesion distribution, and heart failure is an important symptom in PaBV-infected parrots.

Adenocarcinoma of the distal esophagus and esophageal-proventricular junction in a yellow-naped parrot

A 57-y-old male yellow-naped parrot (Amazona auropalliata) was presented because of lethargy, inappetence, and weight loss. Hematology and serum biochemistry were unremarkable, and imaging revealed a mass in the distal esophagus at the coelomic inlet. The luminal diameter of the esophagus was reduced in this area, and passage of ingesta was limited. Following gavage feeding, the patient died and was submitted for autopsy. At postmortem examination, the noted mass effect was a thickening of the distal esophagus with adherent, coalescing, soft, pale-tan plaques on the mucosal surface. Additional gross findings included pale-tan, opaque feed material oozing from the dorsum of the lungs and covering the cranial air sacs. Histology of the esophagus, esophageal-proventricular junction, and proximal proventriculus revealed an unencapsulated, infiltrative, transmural neoplasm that extended from the mucosal surface deep into the muscularis, almost to the adventitia. The neoplasm was composed of cuboidal cells arranged in islands and tubules, consistent with an adenocarcinoma, a rarely reported entity in the esophagus of psittacine birds and to our knowledge not reported previously at the esophageal-proventricular junction.

PARROT BORNAVIRUSES IN PSITTACINES KEPT IN CAPTIVITY IN THE STATE OF SANTA CATARINA, BRAZIL

Parrot bornaviruses are responsible for proventricular dilatation disease (PDD) in psittacines. This study aimed to determine the occurrence and factors associated with Parrot bornaviruses infection in psittacines kept in captivity in a state in the southern region of Brazil. A cross-sectional study was carried out with 192 birds from two facilities (A and B) in 2019, using choanal, esophageal, and cloacal swabs and feathers, totaling 768 samples subjected to reverse-transcription polymerase chain reaction (RT-PCR), for the matrix (M) protein gene with a final product of 350 base pairs (bp). Genetic sequencing of three positive samples was performed by the Sanger method. In the study, the overall virus occurrence was 35.9% (69/192), with 40.4% (42/104) in Facility A and 30.7% (27/88) in Facility B. Sequencing analysis of the samples revealed the presence of Parrot bornavirus 2 (PaBV-2) in both facilities. Swab samples from the choanal (40/69), esophageal (30/69), cloacal (35/69), and feather (15/69) tested positive, facilitating the molecular diagnosis of Parrot bornaviruses. The results indicated that there is no single ideal sample type for antemortem molecular diagnosis of this virus. Simultaneously testing all four samples at the same time point yielded more diagnoses than testing any single sample among the four. Most of the 29 sampled psittacine species were native, and 46.9% of the birds (90/192) consisted of endangered species. Among the psittacines that tested positive, 88.4% (61/69) were clinically healthy, and 8.7% (6/69) exhibited clinical or behavioral signs, including behavioral changes, alterations in feathering, and changes in body score at the time of collection. This study showcases the application of minimally invasive sampling for diagnosing Parrot bornaviruses, enabling sample collection when the birds are restrained for clinical evaluation. This approach facilitates a prompt and effective antemortem diagnosis, thereby serving as an efficient screening method for parrots kept in captivity.

Surveillance of Parrot Bornavirus in Taiwan Captive Psittaciformes

Parrot bornavirus (PaBV) is an infectious disease linked with proventricular dilatation disease (PDD) with severe digestive and neurological symptoms affecting psittacine birds. Despite its detection in 2008, PaBV prevalence in Taiwan remains unexplored. Taiwan is one of the leading psittacine bird breeders; hence, understanding the distribution of PaBV aids preventive measures in controlling spread, early disease recognition, epidemiology, and transmission dynamics. Here, we aimed to detect the prevalence rate of PaBV and assess its genetic variation in Taiwan. Among 124 psittacine birds tested, fifty-seven were PaBV-positive, a prevalence rate of 45.97%. Most of the PaBV infections were adult psittacine birds, with five birds surviving the infection, resulting in a low survival rate (8.77%). A year of parrot bornavirus surveillance presented a seasonal pattern, with peak PaBV infection rates occurring in the spring season (68%) and the least in the summer season (25%), indicating the occurrence of PaBV infections linked to seasonal factors. Histopathology reveals severe meningoencephalitis in the cerebellum and dilated cardiomyopathy of the heart in psittacine birds who suffered from PDD. Three brain samples underwent X/P gene sequencing, revealing PaBV-2 and PaBV-4 viral genotypes through phylogenetic analyses. This underscores the necessity for ongoing PaBV surveillance and further investigation into its pathophysiology and transmission routes.

Antiviral Chemotherapy in Avian Medicine-A Review

This review article describes the current knowledge about the use of antiviral chemotherapeutics in avian species, such as farm poultry and companion birds. Specific therapeutics are described in alphabetical order including classic antiviral drugs, such as acyclovir, abacavir, adefovir, amantadine, didanosine, entecavir, ganciclovir, interferon, lamivudine, penciclovir, famciclovir, oseltamivir, ribavirin, and zidovudine, repurposed drugs, such as ivermectin and nitazoxanide, which were originally used as antiparasitic drugs, and some others substances showing antiviral activity, such as ampligen, azo derivates, docosanol, fluoroarabinosylpyrimidine nucleosides, and novel peptides. Most of them have only been used for research purposes and are not widely used in clinical practice because of a lack of essential pharmacokinetic and safety data. Suggested future research directions are also highlighted.

Genetic trends in parrot Bornavirus: a clinical analysis

Parrot Bornavirus (PaBV) has been reported to cause indigestion and other wasting symptoms such as weight loss and lethargy. The pathogenesis of PaBV has yet to be fully elucidated. This study reports PaBV infections in South Korea and suggests a trend in the genetic information gathered from clinical cases. A total of 487 birds with or without clinical symptoms were tested for bornavirus. Twelve of 361 asymptomatic birds tested positive for bornavirus, while 15 of 126 birds with various symptoms tested positive. A segment of approximately 1,540 bps including the N, X, P and M proteins were obtained from 23 of the positive strains and analyzed with other strains found on GenBank that had clinical information. PaBV was type 2 and 4 in South Korea, and certain amino acid sequences showed a difference between symptom presenting animals and asymptomatic animals in the X protein and P protein. When considering that some asymptomatic cases may have been latent infections at the time of examination, it is plausible these trends may grow stronger with time. Majority of PaBV was type 4 in South Korea. If these trends are confirmed, diagnosis of potentially pathogenic PaBVs in a clinical manner will be possible during the early stages of infection.

Borna disease in an adult free-ranging Eurasian beaver (Castor fiber albicus)

Borna disease (BD) associated with a peracute bacterial septicaemia with Escherichia coli was diagnosed in an adult female, naturally infected, free-ranging Eurasian beaver of the subspecies Castor fiber albicus, clinically characterized by weight loss, depression, weakness and gurgled peristaltic sounds. The beaver was euthanized humanely. Necropsy and light microscopy revealed a non-purulent meningoencephalitis with typical mononuclear perivascular cuffs and parenchymal infiltrates. The diagnosis of BD was confirmed by detection of viral antigen and RNA by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). The PCR product was sequenced and cluster analysis revealed a close relationship between endemic clusters in Saxony-Anhalt. This is the first report of naturally occurring BD in a free-ranging Eurasian beaver.

Detection of a new avian bornavirus in barn owl (Tyto alba) by pan-viral microarray

A barn owl (Tyto alba) died with neurological signs compatible with a viral infection. After discarding other possible infections caused by circulating viruses in the area, analysis of the central nervous system using a pan-viral microarray revealed hybridization to canary bornavirus 2 (CnBV-2). Subsequent sequence analysis confirmed the presence of a virus sharing more than 83% identity with CnBV-2. Surprisingly, the new sequence corresponds to a new virus, here named Barn owl Bornavirus 1 (BoBV-1), within the Orthobornavirus serini species. Moreover, it is the first member of this species that has been detected in a non-passerine bird, indicating that Orthobornavirus serini species comprises viruses with a wider range of hosts than previously presumed. The use of this microarray has proven to be an excellent tool for viral detection in clinical samples, with capacity to detect new viral variants. This allows the diagnosis of a great range of viruses, which can cause similar disease symptoms and which identification by PCR methods might be tedious, probably unsuccessful and, in the long run, expensive. This platform is highly useful for a fast and precise viral detection, contributing to the improvement of diagnostic methods.

Evolutionary Analysis of a Parrot Bornavirus 2 Detected in a Sulphur-Crested Cockatoo (Cacatua galerita) Suggests a South American Ancestor

Parrot bornavirus (PaBV) is an RNA virus that causes Proventricular Dilatation Disease (PDD), neurological disorders, and death in Psittaciformes. Its diversity in South America is poorly known. We examined a Cacatua galerita presenting neuropathies, PDD, and oculopathies as the main signs. We detected PaBV through reverse transcription polymerase chain reaction (RT-PCR) and partial sequencing of the nucleoprotein (N) and matrix (M) genes. Maximum likelihood and Bayesian phylogenetic inferences classified it as PaBV-2. The nucleotide identity of the sequenced strain ranged from 88.3% to 90.3% against genotype PaBV-2 and from 80.2% to 84.4% against other genotypes. Selective pressure analysis detected signs of episodic diversifying selection in both the N and M genes. No recombination events were detected. Phylodynamic analysis estimated the time to the most recent common ancestor (TMRCA) as the year 1758 for genotype PaBV-2 and the year 1049 for the Orthobornavirus alphapsittaciforme species. Substitution rates were estimated at 2.73 × 10-4 and 4.08 × 10-4 substitutions per year per site for N and M, respectively. The analysis of population dynamics showed a progressive decline in the effective population size during the last century. Timescale phylogeographic analysis revealed a potential South American ancestor as the origin of genotypes 1, 2, and 8. These results contribute to our knowledge of the evolutionary origin, diversity, and dynamics of PaBVs in South America and the world. Additionally, it highlights the importance of further studies in captive Psittaciformes and the potential impact on endangered wild birds.

Diving deep into fish bornaviruses: Uncovering hidden diversity and transcriptional strategies through comprehensive data mining

Recently, we discovered two novel orthobornaviruses in colubrid and viperid snakes using an in silico data-mining approach. Here, we present the results of a screening of more than 100,000 nucleic acid sequence datasets of fish samples from the Sequence Read Archive (SRA) for potential bornaviral sequences. We discovered the potentially complete genomes of seven bornavirids in datasets from osteichthyans and chondrichthyans. Four of these are likely to represent novel species within the genus Cultervirus, and we propose that one genome represents a novel genus within the family of Bornaviridae. Specifically, we identified sequences of Wǔhàn sharpbelly bornavirus in sequence data from the widely used grass carp liver and kidney cell lines L8824 and CIK, respectively. A complete genome of Murray-Darling carp bornavirus was identified in sequence data from a goldfish (Carassius auratus). The newly discovered little skate bornavirus, identified in the little skate (Leucoraja erinacea) dataset, contained a novel and unusual genomic architecture (N-Vp1-Vp2-X-P-G-M-L), as compared to other bornavirids. Its genome is thought to encode two additional open reading frames (tentatively named Vp1 and Vp2), which appear to represent ancient duplications of the gene encoding the viral glycoprotein (G). The datasets also provided insights into the possible transcriptional gradients of these bornavirids and revealed previously unknown splicing mechanisms.

Experimental pathogenesis of aquatic bird bornavirus 1 in Pekin ducks

Aquatic bird bornavirus 1 (ABBV-1) is a neurotropic virus that causes persistent infection in the nervous system of wild waterfowl. This study evaluated whether Pekin ducks, the most common waterfowl raised worldwide, are susceptible to ABBV-1 infection and associated disease. Groups of Pekin ducks were inoculated with ABBV-1 through the intracranial (IC; n, 32), intramuscular (IM; n, 30), and choanal (CH; n, 30) routes. Controls (CO; n, 29) received carrier only. At 1, 12, and 21 weeks postinfection (wpi), 7-14 birds were euthanized to assess virus distribution and lesions. Infection rates in the IC and IM groups were over 70%, while only 4 ducks in the CH group became infected. Neurological signs were observed in 8 ducks only, while over 25% of IC and IM birds had encephalitis and/or myelitis. Seroconversion was highest in the IC and IM groups, and mucosal ABBV-1 RNA shedding was most frequent in the IC group (53%). None of the fertile eggs laid during the experiment tested positive for ABBV-1 RNA. This study shows that Pekin ducks are permissive to ABBV-1 infection and partly susceptible to associated disease. While mucosal shedding may be an important route of transmission, congenital infection appears unlikely.

Reverse genetics of parrot bornavirus 4 reveals a unique splicing of the glycoprotein gene that affects viral propagation

Viruses can utilize host splicing machinery to enable the expression of multiple genes from a limited-sized genome. Orthobornaviruses use alternative splicing to regulate the expression level of viral proteins and achieve efficient viral replication in the nucleus. Although more than 20 orthobornaviruses have been identified belonging to eight different viral species, virus-specific splicing has not been demonstrated. Here, we demonstrate that the glycoprotein (G) transcript of parrot bornavirus 4 (PaBV-4; species Orthobornavirus alphapsittaciforme), a highly virulent virus in psittacines, undergoes mRNA splicing and expresses a soluble isoform termed sGP. Interestingly, the splicing donor for sGP is not conserved in other orthobornaviruses, including those belonging to the same orthobornavirus species, suggesting that this splicing has evolved as a PaBV-4-specific event. We have also shown that exogenous expression of sGP does not affect PaBV-4 replication or de novo virion infectivity. In this study, to investigate the role of sGP in viral replication, we established a reverse genetics system for PaBV-4 by using avian cell lines and generated a recombinant virus lacking the spliced mRNA for sGP. Using the recombinant viruses, we show that the replication of the sGP-deficient virus is significantly slower than that of the wild-type virus and that the exogenous expression of sGP cannot restore its propagation efficiency. These results suggest that autologous or controlled expression of sGP by splicing may be important for PaBV-4 propagation. The reverse genetics system for avian bornaviruses developed here will be a powerful tool for understanding the replication strategies and pathogenesis of avian orthobornaviruses. IMPORTANCE Parrot bornavirus 4 (PaBV-4) is the dominant cause of proventricular dilatation disease, a severe gastrointestinal and central nervous system disease among avian bornaviruses. In this study, we discovered that PaBV-4 expresses a soluble isoform of glycoprotein (G), called sGP, through alternative splicing of the G mRNA, which is unique to this virus. To understand the role of sGP in viral replication, we generated recombinant PaBV-4 lacking the newly identified splicing donor site for sGP using a reverse genetics system and found that its propagation was significantly slower than that of the wild-type virus, suggesting that sGP plays an essential role in PaBV-4 infection. Our results provide important insights not only into the replication strategy but also into the pathogenesis of PaBV-4, which is the most prevalent bornavirus in captive psittacines worldwide.

Bornaviral infections in Atlantic canaries (Serinus canaria) in Poland

ABSTRACTThe presence of canary bornavirus (Orthobornavirus serini) genetic material was tested in organ samples from 157 Atlantic canaries (Serinus canaria) and four hybrids of Atlantic canary and European goldfinch (Carduelis carduelis). The subject of the research were samples collected in the years 2006-2022. A positive result was obtained in 16 canaries and one hybrid (10,5%). Eleven positive canaries had neurological signs prior to death. Four of them also had atrophic changes in the forebrain, which have not been described so far in canaries and other species of birds infected with avian bornavirus. In one canary computed tomography without contrast was performed. This study showed no changes, despite advanced forebrain atrophy found on post-mortem examination of the bird. The organs of the studied birds were also tested with PCR tests for the presence of polyomaviruses and circoviruses. There was no correlation between the bornavirus infection and the presence of the other two viruses in the tested canaries.

Structural and biophysical characterization of the Borna disease virus 1 phosphoprotein

Bornaviruses are RNA viruses with a mammalian, reptilian, and avian host range. The viruses infect neuronal cells and in rare cases cause a lethal encephalitis. The family Bornaviridae are part of the Mononegavirales order of viruses, which contain a nonsegmented viral genome. Mononegavirales encode a viral phosphoprotein (P) that binds both the viral polymerase (L) and the viral nucleoprotein (N). The P protein acts as a molecular chaperone and is required for the formation of a functional replication/transcription complex. In this study, the structure of the oligomerization domain of the phosphoprotein determined by X-ray crystallography is reported. The structural results are complemented with biophysical characterization using circular dichroism, differential scanning calorimetry and small-angle X-ray scattering. The data reveal the phosphoprotein to assemble into a stable tetramer, with the regions outside the oligomerization domain remaining highly flexible. A helix-breaking motif is observed between the α-helices at the midpoint of the oligomerization domain that appears to be conserved across the Bornaviridae. These data provide information on an important component of the bornavirus replication complex.

Vaccination against Borna Disease: Overview, Vaccine Virus Characterization and Investigation of Live and Inactivated Vaccines

(1) Background: Vaccination of horses and sheep against Borna disease (BD) was common in endemic areas of Germany in the 20th century but was abandoned in the early 1990s. The recent occurrence of fatal cases of human encephalitis due to Borna disease virus 1 (BoDV-1) has rekindled the interest in vaccination. (2) Methods: The full genomes of the BD live vaccine viruses "Dessau" and "Giessen" were sequenced and analyzed for the first time. All vaccination experiments followed a proof-of-concept approach. Dose-titration infection experiments were performed in rabbits, based on both cell culture- and brain-derived viruses at various doses. Inactivated vaccines against BD were produced from concentrated cell culture supernatants and investigated in rabbits and horses. The BoDV-1 live vaccine "Dessau" was administered to horses and antibody profiles were determined. (3) Results: The BD live vaccine viruses "Dessau" and "Giessen" belong to clusters 3 and 4 of BoDV-1. Whereas the "Giessen" virus does not differ substantially from field viruses, the "Dessau" virus shows striking differences in the M gene and the N-terminal part of the G gene. Rabbits infected with high doses of cell-cultured virus developed neutralizing antibodies and were protected from disease, whereas rabbits infected with low doses of cell-cultured virus, or with brain-derived virus did not. Inactivated vaccines were administered to rabbits and horses, following pre-defined vaccination schemes consisting of three vaccine doses of either adjuvanted or nonadjuvanted inactivated virus. Their immunogenicity and protective efficacy were compared to the BD live vaccine "Dessau". Seventy per cent of horses vaccinated with the BD live vaccine "Dessau" developed neutralizing antibodies after vaccination. (4) Conclusion: Despite a complex evasion of immunological responses by bornaviruses, some vaccination approaches can protect against clinical disease. For optimal effectiveness, vaccines should be administered at high doses, following vaccination schemes consisting of three vaccine doses as basic immunization. Further investigations are necessary in order to investigate and improve protection against infection and to avoid side effects.

Reverse Genetics and Artificial Replication Systems of Borna Disease Virus 1

Borna disease virus 1 (BoDV-1) is a neurotropic RNA virus belonging to the family Bornaviridae within the order Mononegavirales. Whereas BoDV-1 causes neurological and behavioral disorders, called Borna disease (BD), in a wide range of mammals, its virulence in humans has been debated for several decades. However, a series of case reports in recent years have established the nature of BoDV-1 as a zoonotic pathogen that causes fatal encephalitis in humans. Although many virological properties of BoDV-1 have been revealed to date, the mechanism by which it causes fatal encephalitis in humans remains unclear. In addition, there are no effective vaccines or antiviral drugs that can be used in clinical practice. A reverse genetics approach to generating replication-competent recombinant viruses from full-length cDNA clones is a powerful tool that can be used to not only understand viral properties but also to develop vaccines and antiviral drugs. The rescue of recombinant BoDV-1 (rBoDV-1) was first reported in 2005. However, due to the slow nature of the replication of this virus, the rescue of high-titer rBoDV-1 required several months, limiting the use of this system. This review summarizes the history of the reverse genetics and artificial replication systems for orthobornaviruses and explores the recent progress in efforts to rescue rBoDV-1.

Transcriptome Analysis of Duck and Chicken Brains Infected with Aquatic Bird Bornavirus-1 (ABBV-1)

Aquatic bird bornavirus 1 (ABBV-1) is a neurotropic virus that infects waterfowls, resulting in persistent infection. Experimental infection showed that both Muscovy ducks and chickens support persistent ABBV-1 infection in the central nervous system (CNS), up to 12 weeks post-infection (wpi), without the development of clinical disease. The aim of the present study was to describe the transcriptomic profiles in the brains of experimentally infected Muscovy ducks and chickens infected with ABBV-1 at 4 and 12 wpi. Transcribed RNA was sequenced by next-generation sequencing and analyzed by principal component analysis (PCA) and differential gene expression. The functional annotation of differentially expressed genes was evaluated by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The PCA showed that the infected ducks sampled at both 4 and 12 wpi clustered separately from the controls, while only the samples from the chickens at 12 wpi, but not at 4 wpi, formed a separate cluster. In the ducks, more genes were differentially expressed at 4 wpi than 12 wpi, and the majority of the highly differentially expressed genes (DEG) were upregulated. On the other hand, the infected chickens had fewer DEGs at 4 wpi than at 12 wpi, and the majority of those with high numbers of DEGs were downregulated at 4 wpi and upregulated at 12 wpi. The functional annotation showed that the most enriched GO terms were immune-associated in both species; however, the terms associated with the innate immune response were predominantly enriched in the ducks, whereas the chickens had enrichment of both the innate and adaptive immune response. Immune-associated pathways were also enriched according to the KEGG pathway analysis in both species. Overall, the transcriptomic analysis of the duck and chicken brains showed that the main biological responses to ABBV-1 infection were immune-associated and corresponded with the levels of inflammation in the CNS.

Canary Bornavirus (Orthobornavirus serini) Infections Are Associated with Clinical Symptoms in Common Canaries (Serinus canaria dom.)

While parrot bornaviruses are accepted as the cause of proventricular dilatation disease (PDD) in psittacine birds, the pathogenic role of bornaviruses in common canaries is still unclear. To answer the question of whether canary bornaviruses (species Orthobornavirus serini) are associated with a PDD-like disease in common canaries (Serinus canaria f. dom.), the clinical data of 201 canary bird patients tested for bornaviruses using RT-PCR assays, were analyzed for the presence of PDD-like gastrointestinal or central nervous system signs and for other viruses (mainly circovirus and polyomavirus), yeasts and trichomonads. Canary bornavirus RNA was detected in the clinical samples of 40 out of 201 canaries (19.9%) coming from 28 of 140 flocks (20%). All nucleotide sequences obtained could unequivocally be determined as canary bornavirus 1, 2, or 3 supporting the current taxonomy of the species Orthobornavirus serini. PDD-like signs were found associated with canary bornavirus detection, and to a lesser extent, with circoviruses detection, but not with the detection of polyomaviruses, yeasts or trichomonads. The data indicate that canary bornaviruses contribute to a PDD-like disease in naturally infected canaries, and suggest a promoting effect of circoviruses for the development of PDD-like signs.

Tissue Distribution of Parrot Bornavirus 4 (PaBV-4) in Experimentally Infected Young and Adult Cockatiels (Nymphicus hollandicus)

Proventricular dilatation disease (PDD) caused by parrot bornavirus (PaBV) infection is an often-fatal disease known to infect Psittaciformes. The impact of age at the time of PaBV infection on organ lesions and tissue distribution of virus antigen and RNA remains largely unclear. For this purpose, tissue sections of 11 cockatiels intravenously infected with PaBV-4 as adults or juveniles, respectively, were examined via histology, immunohistochemistry applying a phosphoprotein (P) antibody directed against the bornaviral phosphoprotein and in situ hybridisation to detect viral RNA in tissues. In both groups of adult- and juvenile-infected cockatiels, widespread tissue distribution of bornaviral antigen and RNA as well as histologic inflammatory lesions were demonstrated. The latter appeared more severe in the central nervous system in adults and in the proventriculus of juveniles, respectively. During the study, central nervous symptoms and signs of gastrointestinal affection were only demonstrated in adult birds. Our findings indicate a great role of the age at the time of infection in the development of histopathological lesions and clinical signs, and thus provide a better understanding of the pathogenesis, possible virus transmission routes, and the development of carrier birds posing a risk to psittacine collections.