Inoculation induced persistent infection, clinical signs, and seroconversion.
Different avian bornavirus (ABV) genotypes have recently been detected in psittacine birds with proventricular dilatation disease (PDD), an inflammatory fatal central and peripheral nervous system disorder. An indirect immunofluorescence assay (IIFA) for intra vitam demonstration of ABV-specific serum antibodies was established since reverse transcription-PCR (RT-PCR) assays may not detect all ABV variants.
Psittaciform 1 bornavirus (PaBV) has already been shown to be the aetiologic agent of proventricular dilatation disease, a significant disease of birds. However, the pathogenesis of PaBV infection has not yet been resolved and valid data regarding the pathogenicity of different PaBV species are lacking. Thus, the present study was aimed to characterize the influence of two different PaBV species on the course of disease. Eighteen cockatiels were inoculated intracerebrally (i.c.) or intravenously (i.v.) with a PaBV-2 isolate under the same conditions as in a previous study using PaBV-4. Birds were surveyed and sampled for 33 weeks to analyse the course of infection and disease in comparison to that of PaBV-4. Similar to PaBV-4, PaBV-2 induced a persistent infection with seroconversion (from day 6 p.i. onwards) and shedding of viral RNA (from day 27 p.i. onwards). However, in contrast to PaBV-4, more birds displayed clinical signs and disease progression was more severe. After PaBV-2 infection, 12 birds exhibited clinical signs and 10 birds revealed a dilated proventriculus in necropsy. After PaBV-4 infection only four birds revealed clinical signs and seven birds showed a dilatation of the proventriculus. Clinically, different courses of disease were observed after PaBV-2 infection, mainly affecting the gastrointestinal tract. This had not been detected after PaBV-4 infection where more neurological signs were noted. The results provide evidence for different disease patterns according to different PaBV species, allowing the comparison between the infection with two PaBV species, and thus underlining the role of viral and individual host factors for disease outcome.
A total of 1442 live birds and 73 dead birds out of 215 bird collections in Spain, Germany, Italy, the UK and Denmark were tested for avian bornavirus (ABV) infection by four different methods. The majority of the birds were psittacines belonging to 54 different genera of the order Psittaciformes. In total, 22.8% of the birds reacted positive for ABV in at least one of the tests. Combined testing of swabs from the crop and cloaca, and serum for the diagnosis of ABV infection in live birds revealed that virus shedding and antibody production coincided in only one-fifth of the positive birds so that the examination of these three samples is recommended for reliable ABV diagnosis. By statistical analysis of this large number of samples, the ABV infection proved to be highly significant (P B0.001) associated with histopathologically confirmed proventricular dilatation disease (PDD) in dead birds as well as with clinically assumed PDD in live birds. However, ABV infection was also detected in psittacines without pathological lesions or clinical signs of PDD. Twelve non-psittacine birds belonging to the genera Aburria, Ciconia, Geopelia, Leucopsar and Pavo were tested negative for ABV infection. Within the order of Psittaciformes, birds belonging to 33 different genera reacted positive for ABV. In 16 of these psittacine genera, the ABV infection was demonstrated for the first time. The present study emphasizes the widespread occurrence of clinically variable ABV infections in Europe by analysing a large number of specimens from a broad range of bird species in several assays.
To study the course of natural avian bornavirus (ABV) infection, 63 psittacines of three bird collections where ABV had been demonstrated were investigated over a period of 1 yr. The psittacines were clinically observed and swabs of crop and cloaca as well as serum samples were collected three separate times at intervals of 2-6 mo. According to the results of detection of ABV RNA by reverse transcriptase polymerase chain reaction (RT-PCR) and of anti-ABV antibodies by indirect immunofluorescence assay (IIFA), 43 of the birds were found to be infected with ABV. Based on variations in virus shedding and antibody production in combination with the occurrence of proventricular dilatation disease (PDD) -related clinical signs, pathological findings, and lethal outcome, four different groups of infected psittacines and a fifth group of noninfected psittacines were identified. Group 1 comprised six birds with various courses of ABV infection and forms of clinical PDD. Groups 2-4 included all birds with subclinical ABV infections: Group 2 contained 13 birds that were consistently (subgroup A, 6 birds) or inconsistently (subgroup B, 7 birds) ABV positive by PCR and serology; group 3 was composed of 13 psittacines exhibiting only anti-ABV antibodies; and 8 birds that had positive ABV RNA detection in crop and cloaca, but did not develop anti-ABV specific antibodies, were classified in group 4. Twenty-three out of the 63 psittacines remained free of detectable ABV RNA or anti-ABV antibodies over the whole observation period (group 5). Based on the results, it seems that birds with high ABV RNA load in crop and cloaca combined with high anti-ABV antibodies have a high risk of the development of PDD, indicating that the humoral antibodies do not protect against the disease. The meaning of the detection of ABV RNA and antibodies at a low and inconsistent level for the single bird as well as for the epidemiology of the ABV infection remained unclear in this field study and needs to be further investigated.
The aim of this study was to determine the natural infection route of parrot bornavirus (PaBV), the causative agent of proventricular dilatation disease (PDD) in psittacines. For this purpose, nine cockatiels ( Nymphicus hollandicus ) were inoculated orally, and nine cockatiels were inoculated intranasally, with a PaBV-4 isolate. To compare the results of the trials, the same isolate and the same experimental design were used as in a previous study where infection was successful by intravenous as well as intracerebral inoculation. After inoculation, the birds were observed for a period of 6 mo and tested for PaBV RNA shedding, virus replication, presence of inflammatory lesions, and PaBV-4 antigen in tissues, as well as specific antibody production. In contrast to the previous study involving intravenous and intracerebral infections, clinical signs typical for PDD were not observed in this study. Additionally, anti-PaBV antibodies and infectious virus were not detected in any investigated bird during the study. Parrot bornavirus RNA was detected in only four birds early after infection (1-34 days postinfection). Furthermore, histopathologic examination did not reveal lesions typical for PDD, and PaBV antigen was not detected in any organ investigated by immunohistochemistry. In summary, oral or nasal inoculation did not lead to a valid infection with PaBV in these cockatiels. Therefore it seems to be questionable that the formerly proposed fecal-oral transmission is the natural route of infection in immunocompetent adult or subadult cockatiels.
Avian bornavirus (ABV) has been identified as the cause of proventricular dilatation disease in birds, but the virus is also found in healthy birds. Most studies of ABV have focused on captive birds. We investigated 86 free-ranging psittacine birds in Brazil and found evidence for natural, long-term ABV infection.
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